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From: Advances in Agronomy,
Edited by DONALD L. SPARKS
978-0-12-374360-2
Copyright 2008 Elsevier Inc.
Academic Press.
Author's personal copy
C H A P T E R
S E V E N
Ameliorating Soil Acidity of Tropical
Oxisols by Liming For Sustainable
Crop Production
N. K. Fageria* and V. C. Baligar†
Contents
1. Introduction
2. Distribution and Characteristics of Oxisols
3. Beneficial Effects of Liming
3.1. Neutralizing soil acidity and improving supply of calcium
and magnesium
3.2. Reducing phosphorus immobilization
3.3. Improving activities of beneficial microorganisms
3.4. Reducing solubility and leaching of heavy metals
3.5. Improving soil structure
3.6. Improving nutrient use efficiency
3.7. Controling plant diseases
3.8. Mitigating nitrous oxide emission from soils
4. Disadvantages of Overliming
5. Factors Affecting Lime Requirements
5.1. Quality of liming material
5.2. Soil texture
5.3. Soil fertility
5.4. Crop rotation
5.5. Use of organic manures
5.6. Conservation tillage
5.7. Crop species and genotypes within species
5.8. Interaction of lime with other nutrients
6. Criteria to Determine Liming Material Quantity
6.1. Soil pH
6.2. Base saturation
6.3. Exchangeable aluminum, calcium, and magnesium levels
*
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National Rice and Bean Research Center of EMBRAPA, Caixa Postal 179, Santo Antônio de Goiás,
GO, CEP. 75375-000, Brazil
USDA-ARS-Sustainable Perennial Crops Lab, Beltsville, Maryland 20705-2350
Advances in Agronomy, Volume 99
ISSN 0065-2113, DOI: 10.1016/S0065-2113(08)00407-0
#
2008 Elsevier Inc.
All rights reserved.
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N. K. Fageria and V. C. Baligar
6.4. Aluminum saturation
6.5. Crop responses
7. Methods, Frequency, Depth, and Timing of Lime Application
8. Conclusions
Acknowledgment
References
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Abstract
The greatest potential for expanding the world’s agricultural frontier lies in the
savanna regions of the tropics, which are dominated by Oxisols. Soil acidity and
low native fertility, however, are major constraints for crop production on
tropical Oxisols. Soil acidification is an ongoing natural process which can be
enhanced by human activities or can be controlled by appropriate soil management practices. Acidity produces complex interactions of plant growth-limiting
factors involving physical, chemical, and biological properties of soil. Soil
erosion and low water-holding capacity are major physical constraints for
growing crops on tropical Oxisols. Calcium, magnesium, and phosphorous
deficiencies or unavailabilities and aluminum toxicity are considered major
chemical constraints that limit plant growth on Oxisols. Among biological
properties, activities of beneficial microorganisms are adversely affected by
soil acidity, which has profound effects on the decomposition of organic matter,
nutrient mineralization, and immobilization, uptake, and utilization by plants,
and consequently on crop yields. Liming is a dominant and effective practice to
overcome these constraints and improve crop production on acid soils. Lime is
called the foundation of crop production or ‘‘workhorse’’ in acid soils. Lime
requirement for crops grown on acid soils is determined by the quality of liming
material, status of soil fertility, crop species and cultivar within species, crop
management practices, and economic considerations. Soil pH, base saturation,
and aluminum saturation are important acidity indices which are used as a basis
for determination of liming rates for reducing plant constraints on acid soils.
In addition, crop responses to lime rate are vital tools for making liming
recommendations for crops grown on acid soils. The objective of this chapter
is to provide a comprehensive and updated review of lime requirements for
improved annual crop production on Oxisols. Experimental data are provided,
especially for Brazilian Oxisols, to make this review as practical as possible for
improving crop production.
1. Introduction
Soil acidity is one of the most yield-limiting factors for crop production.
Land area affected by acidity is estimated at 4 billion ha, representing 30%
of the total ice-free land area of the world (Sumner and Noble, 2003).
About 16.7% of Africa, 6.1% of Australia and New Zealand, 9.9% of
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Ameliorating Soil Acidity
347
Europe, 26.4% of Asia, and 40.9% of America have acid soils (Von Uexkull
and Mutert, 1995). They cover a significant part of at least 48 developing
countries located mainly in tropical areas, being more frequent in Oxisols
and Ultisols in South America and in Oxisols in Africa (Narro et al., 2001).
In tropical South America, 85% of the soils are acidic, and 850 million ha
of this area is underutilized (Fageria and Baligar, 2001). Acid and low
fertility Oxisols and Ultisols cover about 43% of the tropics (Sanchez and
Logan, 1992). Most of the central part of Brazil is tropical savanna, known as
the cerrado, and covers about 205 million ha or 23% of the country. Most of
the soils in this region are Oxisols (46%), Ultisols (15%), and Entisols (15%),
with low natural soil fertility, high aluminum saturation, and high P fixation
capacity (Fageria and Stone, 1999). Although low fertility is characteristic of
acid soils, these vast areas have a large proportion of favorable topography for
agriculture, adequate temperatures for plant growth throughout the year,
sufficient moisture availability year round in 70% of the region, and for 6–9
months in the remaining 30% of the region (Narro et al., 2001). When the
chemical constraints are eliminated by liming and using adequate amounts
of fertilizers, the productivity of Oxisols and Ultisols is among the highest in
the world (Sanchez and Salinas, 1981).
Theoretically, soil acidity is quantified on the basis of hydrogen (Hþ) and
aluminum (Al3þ) concentrations of soils. For crop production, however,
soil acidity is a complex of numerous factors involving nutrient/element
deficiencies and toxicities, low activities of beneficial microorganisms, and
reduced plant root growth which limits absorption of nutrients and water
(Fageria and Baligar, 2003a). In addition, acid soils have low water-holding
capacity and are subject to compaction and water erosion (Fageria and
Baligar, 2003a). The situation is further complicated by various interactions
among these factors (Foy, 1992). The components of the soil acidity complex
have been thoroughly discussed in various publications (Foy, 1984, 1992;
Kamprath and Foy, 1985; Tang and Rengel, 2003).
Soils become acidic for several reasons. The most common source of
hydrogen is the reaction of aluminum ions with water. The equation for this
reaction in very acid soils (pH<4.0) is:
Al3þ þ H2 O , AlðOHÞ2þ þ Hþ
The species of aluminum ions present vary with pH. Potassium chloride
extracted Al and Al saturation has an inverse relationship with pH (Chartres
et al., 1990; Kariuki et al., 2007). Increased soil acidity causes solubilization
of Al, which is the primary source of toxicity to plants at pH below 5.5
(Bohn et al., 2001; Carson and Dixon, 1979; Ernani et al., 2002; Kariuki et al.,
2007; Parker et al., 1989). The forms of aluminum are mostly exchangeable
Al3þ under very acidic conditions (pH<4.5) to aluminum-hydroxyl ions at
higher pH (4.5–6.5) (Carson and Dixon, 1979). In general, the net positive
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N. K. Fageria and V. C. Baligar
charge of the hydroxyl aluminum species decreases as the pH increases and
then becomes negative in the alkaline pH range. The species of aluminum
ions generates hydrogen ions through a series of hydrolysis reactions shown
below (Lindsay, 1979):
Al3þ þ H2 O , AlðOHÞ2þ þ Hþ
þ
Al3þ þ 2H2 O , AlðOHÞ þ
2 þ 2H
Al3þ þ 3H2 O , AlðOHÞ 03 þ 3Hþ
þ
Al3þ þ 4H2 O , AlðOHÞ 4 þ 4H
þ
Al3þ þ 5H2 O , AlðOHÞ 2
5 þ 5H
The exchangeable Al3þ precipitates as insoluble Al hydroxyl species as
pH increases and is reported to decrease 1000-fold for each unit increase in
pH (Lindsay, 1979). However, at pH values greater than 6.5, Al becomes
increasingly soluble as negatively charged aluminates form (Haynes, 1984).
The Al(OH)2þ species is of minor importance and exists over only a narrow
pH range. The Al3þ ion is predominant below pH 4.7, Al(OH)þ2 between
pH 4.7 and pH 6.5, Al(OH)30 between pH 6.5 and pH 8.0, Al(OH)4
above pH 8.0, and Al (OH)52 species occurs at pH values above those
usually found in soils (Bohn et al., 2001).
Soils become acidic due to the parent material being acidic and naturally
low in the basic cations such as Ca2þ, Mg2þ, Kþ, and Naþ or due to leaching
of these elements down the soil profile by excess rains. This situation is
common in high rainfall areas, where precipitation exceeds evaporation, and
leads to leaching. Soil acidity may also be produced by long-time use of
ammonium fertilizers, removal of cations in the harvested portion of crops
and leaching process, and release of organic acids in decomposition of
crop residues and added organic wastes (Fageria et al., 1990; Sparks, 2003).
Use of adequate amounts of nitrogen fertilizer is fundamental for higher yield
of crops under all ecosystems. Urea and ammonium sulfate are dominant
nitrogen carriers used for crop production around the world. The acidification
of soils by using the ammonium form of nitrogen fertilizers can be explained
by the following equation:
þ
NHþ
4 þ 2O2 , NO3 þ H2 O þ 2H
The oxidation of NH4þ in the above equation is known as nitrification
and hetrotrophic and autrotrophic bacterias can carry it out. The most
important autrotrophic genera of bacteria are Nitrosomonas and Nitrobacter.
Use of legume crops continuously or in rotation can increase soil acidity.
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349
In Australia and New Zealand, continuous cultivation of legume crops
decreased the pH of agricultural soils (Bolan and Hedley, 2003). Legumebased pastures also increased soil acidification (Loss et al., 1993; Williams,
1980). Williams (1980) reported that even the normal growth of clover
pasture for 50 years decreased the pH of an Australian soil from 6.0 to 5.0 at
a depth of 30 cm. Legumes also increase soil acidification in arable cropping
systems (Burle et al., 1997). The reason for generating acidity is associated
with higher absorption of basic cations by these crops and the release of Hþ
ions by the root of legume crops to maintain ionic balance (Bolan and
Hedley, 2003). According to Bolan and Hedley (2003), for different legume
species about 0.2–0.7 mol of Hþ were released per mol N2 fixed. These
authors also state that the amount of Hþ ions released during N2 fixation is
really a function of carbon assimilation and hence depends mainly on the
form and amount of amino acids and organic acids synthesized within the
plants. Soil acidification is also caused by the release of protons (Hþ) during
the transformation and cycling of carbon, nitrogen, and sulfur in the soil–
plant–animal system (Bolan and Hedley, 2003; Robson, 1989). Soil acidification is caused by acid precipitation, the result of industrial pollution (Foy,
1984; Ulrich et al., 1980).
For a long time, acid soils have been considered less suitable for productive agriculture. However, the generation of modern technology, through
intensive research, has brought forth a new reality of increased productivity
of grains and other food, fiber and feed crops, pastures, and energy products
on these soils. Borlaug and Dowswell (1997) concluded that acid lands are no
longer a marginal agriculture frontier, but the most extensive agriculture
frontier of the world, providing hope for adequate food supply and a better
quality of life for millions of people, especially in the tropics. Within the last
few decades, significant advances have been made in management of acid
soils of the tropics for improving pasture for cattle raising and increasing
productivity of annual and plantation crops (Fageria and Baligar, 2003a;
Sumner and Noble, 2003). However, there still remains much to be done
to develop technologies that are economically viable, environmentally
sound, and socially acceptable.
For increase in food supply on acid soils, sustainable cropping systems are
essential for agronomic, economic, and environmental reasons. Sustainable
crop production is defined as practice that over the long term enhances
environmental quality and the resource base on which agriculture depends,
provides for basic human food and fiber needs, is economically viable, is
social acceptable, and improves the quality of life for farmers and society as a
whole (White et al., 1994). Adequately limed soils enhance the sustainability
of cropping systems because of higher crop yields, lower cost of production,
and reduced environmental pollution. World population reached more
than 6 billion in 2007, and is expected to increase to 8 billion by 2025
and over 9 billion by 2050. Over half of the world population currently lives
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N. K. Fageria and V. C. Baligar
in regions dominated by acid soils (Yang et al., 2004). The greatest potential
for expanding the world’s agricultural frontier lies in the tropical savanna
regions dominated by acid, infertile soils classified mainly as Oxisols and
Ultiosls (Sanchez and Salinas, 1981). Furthermore, about 95% of the current
population growth has taken place in tropical regions; therefore, a continuing
increase in food production is required to meet this demand (Hartemink,
2002). Liming is the most important and most effective practice to ameliorate
soil acidity constraints for optimal crop production (Haynes, 1984). The
practice of well-planned and execution of liming under these situations is
fundamental for increasing crop yield on acid soils. The magnitude of the soil
acidity problem of Oxisols in many areas around the world, and the potential
that these soils offer in increasing the production of food and fiber, provides a
focus for the objectives of this review, that is, to review the nature, causes,
and management of Oxisols acidity in order that crop productivity on these
acid soils might be improved for the benefit of humankind.
2. Distribution and Characteristics of Oxisols
The theory concerning the effects of parent materials on soil formation
originated in Russia during the late 19th century. According to this theory,
soil formation is a function of climatic conditions, biotic activities, topography, and time span (West et al., 1998). Soil profile development processes
are known as pedogenic and involve additions, losses, translocations, and
transformations of soil materials (Brady and Weil, 2002). Simonson (1959)
outlined a generalized theory of soil genesis in which he proposed to
consider soil formation as consisting of two overlapping steps: the accumulation of parent materials and the differentiation of horizons in the solum.
The former is largely a geochemical or geogenesis process, whereas the
latter is a pedogenesis process (Van Wambeke, 1991; West et al., 1998).
Information on the extent and distribution of Oxisols in various parts of
the world has increased in recent years. However, soil survey is still incomplete due to lack of infrastructure and low population density in some areas
where Oxisols occur (Buol and Eswaran, 2000). Table 1 shows approximate
areas of Oxisols at global level and in the tropical regions compared with
other soil orders. In the tropics, Oxisols occupy a much larger area than do
other soil orders. Acid and low fertility soils meeting such stereotypic
concept of ‘‘tropical soils’’ are mainly classified as Oxisols and Ultisols.
Because of recent global glaciaton, these soils cover only 7% of the temperate
region but 43% of the tropics (Sanchez and Logan, 1992). The largest
concentration of Oxisols occurs in the South American savannas, the eastern
Amazon, and parts of central Africa (Sanchez and Salinas, 1981). Distribution
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Ameliorating Soil Acidity
Table 1
Approximate distribution of soil orders globally and in tropical regions
Soil order
Global area
(million ha)
Percentage
of total
global area
Area in the
tropics
(million ha)
Percentage
of total
tropical area
Alfisols
Andisols
Aridisols
Entisols
Gelisols
Histosols
Inceptisols
Mollisols
Oxisols
Spodosols
Ultisols
Vertisols
1790
144
2276
2730
1769
240
1547
1100
840
478
1347
311
12.3
1.0
15.6
18.7
12.1
1.6
10.6
7.5
5.8
3.3
9.3
2.2
559
43
87
574
–
36
532
74
833
20
749
163
15.2
1.2
2.4
15.6
–
0.9
14.4
2.0
23.0
0.5
20.4
4.4
Source: Sanchez and Logan (1992), Buol and Eswaran (2000), and Brady and Weil (2002).
Table 2 Distribution of oxisols and ultisols in South America
Country
Area (106 ha)
Total area of
the country (%)
Brazil
Colombia
Peru
Venezuela
Bolivia
Guiana
Surinam
Paraguay
Equador
French Guiana
Chile
Argentina
572.71
67.45
56.01
51.64
39.54
12.25
11.43
9.55
8.61
8.61
1.37
1.28
68
57
44
58
57
62
62
24
23
94
2
0.4
Source: Cochrane (1978).
of Oxisols and Ultisols in South American countries is shown in Table 2.
Extensive areas of Southeast Asia are covered by highly weathered Oxisols
and Ultisols (Ismail et al., 1993; Supriyo et al., 1992; Van Wambeke, 1991;
Von Uexkull and Mutert, 1995). Sanchez and Salinas (1981) reported that
about 15 million ha of Oxisols is found in tropical Asia. Baligar and Ahlrichs
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N. K. Fageria and V. C. Baligar
(1998), Baligar et al. (2004), Van Wambeke (1991), and Von Uexkull
and Mutert (1995) have reported extensively on the distribution, nature,
and properties of acid soils.
Oxisols are also referred to as latosols, laterite, Ferralsols, and red earths.
Oxisols are defined as mineral soils having an oxic horizon which is
characterized by the virtual absence of weathering primary minerals or 2:1
layer silicate clays, the presence of 1:1 layer silicate clays and highly insoluble
minerals such as quartz sand, the presence of hydrated oxides of iron and
aluminum, and the absence of water-dispersible clay (Soil Science Society of
America, 1997). Oxisols are highly weathered acidic soils, having low basic
cation and effective cation exchange capacity (ECEC). The cation exchange
capacity (CEC) refers to the value obtained with 1 M NH4OAc (pH 7), and
ECEC is the sum of exchangeable cations (Al3þ, Ca2þ, Mg2þ, Kþ, and
Naþ) (Sumner and Noble, 2003). These soils have good physical properties
(except low water-holding capacity and susceptibility to erosion) and have
uniform distribution of clay with increasing depth. On average, these soils
have clay contents of more than 300 g kg1. However, the clays are of low
activity and have a limited capacity to hold basic cations. These soils are very
low in plant-available phosphorus and due to high concentration of iron and
aluminum oxides having high P fixation capacity; selected chemical properties of Brazilian Oxisols are presented in Tables 3 and 4.
3. Beneficial Effects of Liming
Modern agriculture production requires the implementation of efficient, sustainable, and environmentally sound management practices. In this
context, liming is an important practice to achieve optimum yields of all crops
grown on acid soils. Liming is the most widely used long-term method of soil
Table 3
Selected chemical properties of Oxisols of the cerrado region of Brazil
Value
pH in
H2O
Organic
matter
(g kg1)
P
(mg kg1)
K
(mg kg1)
Mg
Ca
(cmolc
(cmolc kg1) kg1)
Minimum
Maximum
Mean
S.D.
4.8
6.3
5.5
0.28
8
31
21.5
5.1
0.6
14.8
4.12
2.93
12
73
31.6
13.7
0.54
3.42
1.77
0.70
Source: Compiled from Fageria and Breseghello (2004).
Values are averages of 43 soil samples collected from the State of Mato Grosso.
0.22
2.42
0.84
0.40
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Table 4 Selected soil acidity indices of Oxisols of cerrado region of Brazil
Value
Base
saturation
(%)
Al
saturation
((%)
Ca
Saturation
(%)
Mg
saturation
(%)
K
saturation
(%)
Minimum
Maximum
Mean
SD
9
60
28
10.78
0
26
8
6.33
5
34
18
7.36
2
25
9
4.03
0.25
1.64
0.82
0.31
Source: Compiled from Fageria and Breseghello (2004).
acidity amelioration, and its success is well documented (Conyers et al., 1991;
Haynes, 1982; Kaitibie et al., 2002; Scott et al., 2001). Application of lime at
an appropriate rate brings several chemical and biological changes in the soil,
which are beneficial or helpful in improving crop yields on acid soils.
Adequate liming eliminates soil acidity and toxicity of Al, Mn, and H;
improves soil structure (aeration); improves availabilities of Ca, P, Mo, and
Mg, pH, and N2 fixation; and reduces the availabilities of Mn, Zn, Cu, and Fe
and leaching loss of cations. These beneficial effects are discussed in the
following section.
3.1. Neutralizing soil acidity and improving supply of calcium
and magnesium
Liming raises soil pH, base saturation, and Ca and Mg contents, and reduces
aluminum concentration in Brazilian Oxisols (Fageria, 2000, 2001a; Fageria
and Stone, 2004). The changes in these chemical properties with the use of
dolomitic lime [CaMg (CO3)2] can be explained on the basis of following
equation (Fageria and Baligar, 2005a):
2þ
CaMgðCO3 Þ2 þ 2Hþ , 2HCO þ Mg2þ
3 þ Ca
þ
2HCO
3 þ 2H , 2CO2 þ 2H2 O
CaMgðCO3 Þ2 þ 4Hþ , Ca2þ þ Mg2þ þ 2CO2 þ 2H2 O
The above equations show that acidity-neutralizing reactions of lime occur
in two steps. In the first step, Ca and Mg react with H on the exchange
complex and H is replaced by Ca2þ and Mg2þ on the exchange sites (negatively charged particles of clay or organic matter), forming HCO
3 . In the
þ to form CO and H O to increase pH.
second step, HCO
reacts
with
H
3
2
2
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N. K. Fageria and V. C. Baligar
Soil moisture and temperature and quantity and quality of liming material
mainly determine the reaction rate of lime. To get maximum benefits from
liming or for improving crop yields, liming materials should be applied in
advance of crop sowing and thoroughly mixed into the soil to enhance its
reaction with soil exchange acidity. Selected soil chemical properties influenced
by applied lime in a Brazilian Oxisols are presented in Table 5.
Highly weathered tropical soils such as Oxisols have very low levels of
exchangeable Ca, and crops grown on such soils exhibit Ca deficiency
when exchangeable Ca is <1 cmol/kg (Cregan et al., 1989; Kamprath,
1984). Application of limestone (calcium carbonate) and dolomitic lime
(Ca and Mg bicarbonate) increases soil-exchangeable Ca and Ca and Mg,
respectively. Plant growth improvement in acid soil is not due to addition of
basic cations (Ca, Mg), but because of increasing pH reduces toxicity of
phytotoxic levels of Al and Mn. Increasing concentration of Ca2þ, Kþ, and
Hþ in the soil decreases plant Mg uptake due to competitive inhibition
(Clark, 1984; Marschner, 1995).
Table 5 Influence of liming on selected soil chemical properties of Oxisols at 0–10
and 10–20 cm depth
Lime rate (Mg ha1)
Soil property
0–10 cm depth
pH (1:2.5 soil water)
Base saturation (%)
H þ Al (cmolc kg1)
Acidity saturation (%)
Ca (cmolc kg1)
Mg (cmolc kg1)
10–20 cm depth
pH
Base saturation (%)
H þ Al (cmolc kg1)
Acidity saturation (%)
Ca (cmolc kg1)
Mg (cmolc kg1)
0
12
24
F test
CV (%)
5.4c
28.9c
6.5a
71.1a
1.8c
0.6b
6.7b
72.0b
2.0b
27.8b
3.6b
1.3a
7.1a
84.9a
1.0c
15.1c
4.3a
1.3a
**
**
**
**
**
**
2.0
19
14
14
9
12
5.3c
22.9c
6.6a
77.1a
1.4c
0.4b
6.2b
51.2b
3.8b
49.0b
2.7b
1.0a
6.5a
61.7a
2.9c
38.3c
3.3a
1.1a
**
**
**
**
**
**
3.0
24
13
12
15
15
** Significant at the 1% probability level, respectively. Means followed by the same letter in the same
line under different lime treatments are not statistically significant at the 5% probability level by
Tukey’s test.
Source: Fageria (2006).
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3.2. Reducing phosphorus immobilization
Oxisols are naturally deficient in total and plant-available phosphorus and
significant portions of applied P are immobilized due to either precipitation
of P as insoluble Fe/Al-phosphates or chemisorption to Fe/Al-oxides and
clay minerals (Nurlaeny et al., 1996). Smyth and Cravo (1992) reported that
Oxisols are notorious for P immobilization because they have higher iron
oxide contents in their surface horizons than do any other kind of soil. The
P fixation capacity in Oxisols is directly related to the surface area, and clay
contents of the soil material, and inversely related to SiO2/R2O3 ratios
(Curi and Camargo, 1988).
Bolan et al. (1999) reported that in variable charge soils, a decrease in pH
increases the anion exchange capacity, thereby increasing the retention of P.
Hence, improving crop yields on these soils requires high rates of P
application (Fageria, 1989; Sanchez and Salinas, 1981). Reports regarding
the effects of liming on P availability in highly weathered acid soils are in
conflict (Friesen et al., 1980a; Haynes, 1984). Liming can increase, decrease,
or have no effect on P availability (Anjos and Rowell, 1987; Curtin and
Syers, 2001; Fageria, 1984; Haynes, 1982; Mahler and McDole, 1985).
However, in a recent study, Fageria and Santos (2008) reported a linear
increase in Mehlich 1 extractable P with increasing soil pH in the range of
5.3–6.9 (average of 0–10 and 10–20 cm soil depth) in Brazilian Oxisols
(Fig. 1). Mansell et al. (1984) and Edmeades and Perrott (2004) reported that
in acid soils of New Zealand, primary benefit of liming occurs through an
increase in the availability of P by decreasing P adsorption and stimulating
the mineralization of organic P. Fageria (1984) also reported that in Brazilian Oxisols there was a quadratic increase in the Mehlich 1 extractable P in
the pH range of 5.0–6.5, and thereafter it was decreased. Increase in
availability of P in the pH range of 5.0 to 6.5 was associated with release
of P ions from Al and Fe oxides, which were responsible for P fixation
(Fageria, 1989). At higher pH (>6.5), the reduction of extractable P was
associated with precipitation of P as Ca phosphate (Naidu et al., 1990).
These increases in extractable P or liberation of this element in the pH range
of 5.0–6.5 and reduction in the higher pH range (>6.5) can be explained by
the following equations:
AlPO4 ðP fixedÞ þ 3OH , AlðOHÞ3 þ PO 3
4 ðP releasedÞ
CaðH2 PO4 Þ2 ðsoluble PÞ þ 2Ca2þ , Ca3 ðPO4 Þ2 ðinsoluble PÞ þ 4Hþ
The liming acid soils result in the release of P for plant uptake; this effect
is often referred to as ‘‘P spring effect’’ of lime (Bolan et al., 2003). Bolan et al.
(2003) reported that in soils high in exchangeable and soluble Al, liming
might increase plant P uptake by decreasing Al, rather than by increasing
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Average of two soil depths
40
30
20
Y = - 1.5594 + 4.9585X
R 2 = 0.5417**
Mehlich-1 extractable P (mg kg-1)
10
0
Y = - 5.3937 + 3.9288X
R 2 = 0.4032**
10–20 cm
30
20
10
0
60
0–10 cm
50
40
30
Y = - 3.5026 + 5.7293X
R 2 = 0.4462**
20
10
0
5.0
5.5
6.0
6.5
7.0
7.5
Soil pH in H2O
Figure 1 Relationship between soil pH and Mehlich 1 extractable soil phosphorus
(Fageria and Santos, 2008).
P availability per se. This may be due to improved root growth where Al
toxicity is alleviated, allowing a greater volume of soil to be explored (Friesen
et al., 1980b).
3.3. Improving activities of beneficial microorganisms
Soil microbiological properties can serve as soil quality indicators because
soil microorganisms are the second most important (after plants) biological
agents in the agricultural ecosystem (Fageria, 2002; Yakovchenko et al.,
1996). Soil microorganisms provide the primary driving force for many
chemical and biochemical processes and thus affect nutrient cycling, soil
fertility, and carbon cycling (He et al., 2003). Plant roots and rhizosphere are
colonized by many plant-beneficial microorganisms such as symbiotic and
nonsymbiotic dinitrogen (N2) fixing bacteria, plant growth promoting
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357
rhizobacteria, saprophytic microorganisms, biocontrol agents, and mycorrhizae and free living fungi. Soil acidity restricts the activities of these beneficial
microorganisms, except fungi, which grow well over a wide range of soil pH
(Brady and Weil, 2002). Enhancing the activities of beneficial microbes such as
rhizobia, diazotropic bacteria, and mycorrhizae in the rhizosphere has
improved root growth by the fixation of atmospheric nitrogen, suppressing
pathogens, and producing phytohormones, enhancing root surface area
to facilitate uptake of less mobile nutrients such as P and micronutrients
and mobilizing and solubilizing unavailable nutrients (Baligar and Fageria,
1999).
Literature provides ample evidence that low soil pH adversely affects
activities of rhizobium, including a loss of its ability to fix nitrogen (Angle,
1998). Mulder et al. (1977) showed that low soil pH reduced the activity and
their ability to multiply. Holdings and Lowe (1971) further demonstrated
that low soil pH increased the number of ineffective rhizobia in soil. Angle
(1998) reported that soil pH decline below 5.5 reduced rhizobial populations
and rhizobia that survive such a pH lack the capacity to fix atmospheric
nitrogen. Ibekwe et al. (1995) showed that plants grown in an unamended
control soil with low pH often exhibited low rates of nitrogen fixation.
Ibekwe et al. (1995) also reported high rates of nitrogen fixation when high
concentrations of heavy metals were present, but soil pH was nearly neutral.
Franco and Munns (1982) found that decreasing the pH of nutrient solutions
from 5.5 to 5.0 decreased the number of nodules formed by common bean.
Bacterias are divided into three groups based on their tolerance to soil
acidity. The first group is known as acidophiles (grow well under acidic
conditions), the second group is known as neutrophiles (grow well under
neutral pH), and the third group is known as alkaliphiles (grow well
under alkaline conditions) (Glenn et al., 1997). Soil contains all these groups
of bacteria. Most soil bacterias, however, including the nitrogen fixing rhizobium, belong to the neutrophiles group (Glenn et al., 1997). Therefore, acidic
pH ranges are detrimental to bacterial activities.
Lime ameliorates the harmful effects of soil acidity (Cregan et al., 1989).
Studies on bacteria suggest that the success of liming may be due not only to
an effect on the soil pH but also to a direct effect on the bacteria themselves
(Reeve et al., 1993). Like most neutrophilic bacteria, rhizobia appear to
maintain an intracellular pH between 7.2 and 7.5, even when the external
environment is acidic (Kashket, 1985). However, differences exist between
and among acid-tolerant and acid-sensitive strains (Bhandhari and Nicholas,
1985; Graham et al., 1994). Strain tolerance to lower pH has been reported
for rhizobia (Brockwell et al., 1995) and arbuscular mycorrhizal fungi
(Habte, 1995; Siqueira and Moreira, 1997). Muchovej et al. (1986) reported
that liming of a Brazilian Oxisols improved nodule formation in soybean.
Haynes and Swift (1988) reported that liming increased microbial biomass
and enzyme activity in acid soils.
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Nurlaeny et al. (1996) found that liming increased shoot dry weight, total
root length, and mycorrhizal colonization of roots in soybean and corn
grown on tropical acid soils. These authors also reported that mycorrhizal
colonization improved P uptake and plant growth. Furthermore, colonization of the roots with arbuscular mycorrhizal fungi can increase plant uptake
of P and other nutrients with low mobility, such as Zn and Cu (Marschner
and Dell, 1994). Uptake of P by mycorrhizal plants is usually from the same
labile soil P pool from which the roots of nonmycorrhizal plants take up P
(Morel and Plenchette, 1994). However, the external hyphae can absorb
and translocate P to the host from soil outside the root depletion zone of
nonmycorrhizal roots (Johansen et al., 1993). Thereby, under conditions
where P and other nutrients’ diffusion in soil is slow and root density not
very high, more immobile nutrients are spatially available to mycorrhizal
plants than to nonmycorrhizal plants (Nurlaeny et al., 1996). Furthermore,
mycorrhizal plants may utilize organic soil P due to surface phosphatase
activity of hyphae (Tarafdar and Marschner, 1994, 1995), enhanced activity
of P-solubilizing bacteria in the mycorrhizosphere (Linderman, 1992;
Tarafdar and Marschner, 1995), or reduced immobilization of labile P in
organic matter (Joner and Jakobsen, 1994). Additionally, soil pH affects
arbuscular mycorrhizal colonization (Mamo and Killham, 1987; Wang et al.,
1985), species distribution (Porter et al., 1987), and effectiveness of the
mycorrhizal symbiosis with plant species (Hayman and Tavares, 1985).
3.4. Reducing solubility and leaching of heavy metals
Heavy metals are those metals having densities >5.0 Mg m3 (Soil Science
Society of America, 1997). In soils, these include the elements Cu, Zn, Fe,
Mn, Cd, Co, Cr, Hg, Ni, and Pb. Higher concentrations of these heavy
metals in soil solution can lead to uptake by crop plants in quantities that are
harmful for human and animal health; leaching can also occur and contaminate ground water (Epstein and Bloom, 2005; Hall, 2002). Soil properties
such as organic matter content, clay type, redox status, and soil pH are
considered the major factors determining the bioavailability of heavy metals
in soil (Huang and Chen, 2003; McLean, 1976; Wagner, 1993).
Increasing pH by application of lime to acid soils reduces the solubility of
most heavy metals (Fageria et al., 2002; Lindsay, 1979; Mortvedt, 2000).
In addition, higher soil pH increases the adsorption affinity of iron oxides,
organic matter, and other adsorptive surfaces (Sauve et al., 2000). This
practice can reduce the leaching of heavy metals to ground water as well
as their absorption by plants and consequently improve soil and water
quality and subsequently human health. Data in Tables 6 and 7 show the
influence of increasing base saturation on soil-extractable Mn, Fe, Zn, and
Cu (heavy metals) after harvest of common bean crop grown on Brazilian
Oxisols. These data show that with exception of Cu, concentrations of
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Table 6 Influence of base saturation on DTPA extractable soil Mn and Fe after harvest
of a common bean crop grown on Brazilian Oxisols
Base saturation
(%)
Mn
(mg kg1)
Base saturation
(%)
Fe
(mg kg1)
23.4
54.4
67.5
8.1a
6.4b
5.5b
28.5
65.8
75.3
33.1a
21.1b
20.7b
Means in the same column followed by same letter are not significantly different at 5% probability level
by Tukey’s test.
Source: Fageria and Santos (2005).
Table 7 Influence of base saturation on DTPA extractable soil Zn and Cu after harvest
of common bean crop grown on Brazilian Oxisols
Base saturation
(%)
Zn
(mg kg1)
Base saturation
(%)
Cu
(mg kg1)
26.2
60.1
69.8
5.5a
5.4a
4.8b
23.4
56.7
66.5
3.7a
3.7a
3.5a
Means in the same column followed by same letter are not significantly different at 5% probability level
by Tukey’s test.
Source: Fageria and Santos (2005).
these microelements in the extractant were significantly reduced with
increasing soil base saturation due to liming.
Increasing soil pH with lime can significantly affect the adsorption of
heavy metals in soils (Adriano, 1986; McBride, 1994). Adsorption of Pb,
Cd, Ni, Cu, and Zn is significantly decreased with increasing soil pH (Basta
and Tabatabai, 1992; Elliott et al., 1986; Harter, 1983). Ribeiro et al. (2001)
reported that among several soil amendments (dolomitic lime, gypsum,
vermicompost, sawdust, and solomax), dolomitic lime was most effective
in reducing bioavailabilities of these heavy metals: Zn, Cd, Cu, and Pb.
Most metals are relatively more mobile under acidic and oxidizing conditions and are strongly retained under alkaline and reducing conditions
(Huang and Chen, 2003). Brummer and Herms (1983) reported that Pb,
Cd, Hg, Co, Cu, and Zn are more soluble at pH 4.0–5.0 than in a pH range
of 5.0–7.0. However, under acidic conditions, As, Se, and Mo are less
soluble because of formation of these elements into anionic forms (Huang
and Chen, 2003).
The risk of food-chain contamination by toxic substances and elements
has been a major concern of both producers and consumers (Treder and
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Cieslinski, 2005). The concentrations of heavy metals in plants and their
distribution to various parts of the plant are the result of the combined
influence of soil properties and biological factors. However, translocation of
heavy metals from the soil solids to the soil solution, and thus their availability to plants, depends upon several factors. Soil properties such as organic
matter content, clay type, redox potential, and soil pH are considered the
major factors that determine the bioavailability of heavy metals in soil
(Treder and Cieslinski, 2005). Hence, liming certainly helps in reducing
availability of heavy metals to crop plants.
3.5. Improving soil structure
The clustering of soil particles (sand, silt, and clay) into aggregates or peds
and their arrangement into various patterns resulted in what is termed soil
structure. From the agronomic standpoint, soil structure affects plant
growth through its influence on infiltration, percolation, and retention of
water, soil aeration, and mechanical impedance to root growth. Its general
role in soil–water relations can be evaluated in terms of the extent of soil
aggregation, aggregate stability, and pore size distribution. These soil characteristics change with tillage practices and cropping systems. The major
binding agents responsible for aggregate formation are the silicate clays,
oxides of iron and aluminum, and organic matter and its biological decomposition products. The Oxisols and Ultisols, characterized by dominant
quantities of iron and aluminum oxides, have a high degree of aggregation
and the aggregates are quite stable. The red color of these soils is attributed
to iron oxide minerals.
Calcium in liming materials helps in the formation of soil aggregates,
hence improving soil structure (Chan and Heenan, 1998). The lime-induced
improvement in aggregate stability manifested through the effect of liming
on dispersion and flocculation of soil particles (Bolan et al., 2003). Liming is
often recommended for the successful colonization of earthworm in pasture
soils. The lime-induced increase in earthworm activity may influence soil
structure and macroporosity through the release of polysaccharide and the
burrowing activity of earthworm (Springett and Syers, 1984).
3.6. Improving nutrient use efficiency
Improving nutrient use efficiency is becoming increasingly important in
modern crop production due to rising costs associated with fertilizer inputs
and growing concern about environmental pollution. Nutrient use efficiency
is defined in several ways in the literature. The most common definitions are
known as agronomic efficiency, physiological efficiency, agrophysiological
efficiency, apparent recovery efficiency, and utilization efficiency (Baligar et al.,
2001; Fageria and Baligar, 2003b, 2005a; Fageria et al., 1997). Most of these
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definitions deal with nutrient uptake and utilization by plants in dry matter
production. In a simple way, efficiency is output of economic produce divided
by fertilizer input. This means that a crop species or genotypes of the same
species producing higher dry matter yield with low nutrient application rate or
accumulation are called efficient plant species or genotypes. According to the
Soil Science Society of America (1997), a nutrient-efficient plant is one
that absorbs, translocates, or utilizes more of a specific nutrient than another
plant under conditions of relatively low nutrient availability in the soil or
growth medium. Fischer (1998) reported that rice cultivars released in 1965
produced less than 40 kg of grain per kilogram of N taken up by the plants.
However, cultivars released in 1995 produced almost 55 kg of grain per
kilogram of N take-up, resulting in a more than 35% increase in N efficiency
(Fischer, 1998).
Nutrient use efficiency (recovery efficiency) seldom exceeds 50% in most
grain production systems (Fageria and Baligar, 2005a; Westerman et al.,
2000). Worldwide, N recovery efficiency for cereal production [rice,
wheat, sorghum, millet, barley, corn, oat, and rye is 33% (Raun and
Johnson, 1999]. The low nutrient use efficiency is associated with the use
of low input crop management technology. Such management practices
include use of low rate of fertilizers and lime, water deficiency, inadequate
control of insects, diseases, and weeds, and planting of inefficient plant species
or genotypes of the same species (Fageria, 1992). Low nutrient use efficiency
in crop production systems is undesirable, both economically and
environmentally.
Soil acidity is also responsible for low nutrient use efficiency by crop
plants. Fageria et al. (2004) reported that liming of Oxisols improved the use
efficiency of P, Zn, Cu, Fe, and Mn by upland rice genotypes. Efficiency of
these nutrients was higher under a pH of 6.4 than with pH 4.5. The
improvement in efficiency of these nutrients was associated with decreasing
soil acidity, improving their availability, and enhanced root system
(Fageria et al., 2004).
3.7. Controling plant diseases
Mineral nutrition plays an important role in controling plant diseases.
Healthy plants provided by adequate essential nutrients in appropriate
balance generally have fewer diseases compared with nutrient-deficient
plants (Fageria et al., 1997). When evaluating the effects of mineral nutrition
on plant diseases, in addition to optimal rate of nutrient application an
appropriate nutrient balance is very important. Indiscriminate excess supply
of a nutrient will create imbalance with other nutrients and chances of plant
infestation with diseases will increase. Furthermore, there is still lack of
systematic research data to determine the effects of mineral nutrition
on plant diseases, involving soil scientists and plant pathologists. Plant
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pathologists without collaboration of soil scientists have conducted most of
the studies in this discipline, and invariably, with very inappropriate fertilizer rates (excess or deficient). In addition, most of the research data related
to nutrient–disease interactions are collected under controlled growth
conditions and field studies are lacking.
However, existing information suggests that in some cases liming decreases
diseases and in others the inverse is true. It has been known for nearly 100
years that amending the soil with CaCO3 would provide a significant measure
of clubroot (Plasmodiphora brassicae Wor.) control in crucifers (Engelhard,
1989). Conversely, many diseases of potato (Solanum tuberosum L.), such as
common scab (Streptomyces scabies), powdery scab (Spongospora subterranea),
black scurf (Rhizoctonia solani), and tuber blight (Phytophthera infestans),
are favored at higher pH compared to lower pH (Haynes, 1984).
Calcium has been implicated in plant resistance to several plant pathogens, including Erwinia phytophthora, R. solani,Sclerotium rolfsii, and Fusarium
oxysporum (Kiraly, 1976). Haynes (1984) reported that calcium forms rigid
linkages with pectic chains and thus promotes the resistance of plant cell
walls to enzymatic degradation by pathogens.
Information is lacking on effects of lime on damage by specific insects on
plants. Overall, from the available data, it appears that variable levels of
macro- and micronutrients in plants have positive to negative or no effects
on insect damage to crop plants (Fageria and Scriber, 2002). Lime improves
the availability of Ca, Mg, Mo, and P and reduces the availability of Mn,
Zn, Cu, and Fe. It would be interesting to evaluate how such changes in
availabilities of these nutrients in soil affect insect damage in plant.
3.8. Mitigating nitrous oxide emission from soils
Nitrous oxide (N2O) is globally important, due to its role as a greenhouse gas,
and once oxidized to NOx it can catalyze stratospheric ozone destruction.
Nitrous oxide is a potent greenhouse gas with much greater global warming
potential than CO2 (Izaurralde et al., 2004). Nitrous oxide concentration in
the atmosphere has increased since preindustrial times and agricultural lands
are the main anthropogenic sources (Clough et al., 2004; Perez et al., 2001).
The concentration of N2O in the atmosphere, estimated at 2.68102 mL
L1 around 1750, has increased by about 17% as a result of human alterations
of the global N cycle (IPCC, 2001). Global annual N2O emissions from
agricultural soils have been estimated to range between 1.9 and 4.2 Tg N,
with about half arising from anthropogenic sources (IPCC, 2001).
Since soil pH has a potential effect on N2O production pathways, and
the reduction of N2O to N2, it has been suggested that liming may provide
an option for the mitigation of N2O emission from agricultural soils
(Stevens et al., 1998). Clough et al. (2003, 2004) reported that liming
has been promoted as a mitigation option for lowering soil N2O emissions
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when soil moisture content is maintained at field capacity. Nitrous oxide
forms in soils primarily during the process of denitrification (Robertson and
Tiedje, 1987) and to a lesser extent during nitrification (Tortoso and
Hutchinson, 1990).
4. Disadvantages of Overliming
Adequate lime rate is essential not only for maximum economic return
but also for maintaining appropriate nutrient balance for crop production.
Overliming effects are more pronounced on coarse-textured soils than on
fine-textured soils. Fine-textured soils have high buffer capacity; hence,
changes in chemical properties due to liming are not as pronounced as for
coarse-textured soils. Overliming can create deficiencies of micronutrients
like Fe, Mn, Zn, Cu, and B. These nutrients are usually adsorbed onto
sesquioxide soil surfaces. Table 8 summarizes important changes in micronutrient concentrations as influenced by soil pH and consequent acquisition
by plants. Table 9 shows acquisition of Zn, Cu, Fe, and Mn by upland rice
grown at various soil pH levels on Brazilian Oxisols. Uptake of these
micronutrients has been significantly decreased at higher pH levels. Iron
deficiency in upland rice in Brazilian Oxisols is commonly observed with
pH higher than 6.5 (Fageria, 2000; Fageria et al., 1994, 2002). Similarly,
shoot dry matter, grain yield, and number of panicles in upland rice were
significantly decreased with increasing pH in the range of 4.6–6.8 in
Brazilian Oxisols (Table 10).
The reaction responsible for the reduced solubility of Fe with increasing
pH is well understood. It results in the precipitation of Fe (OH)3 as the
concentration of OH ions is increased as indicated by the following reaction:
Fe3þ þ 3OH , FeðOHÞ3 ðprecipitationÞ
The Fe(OH)3 is chemically equivalent to the hydrated oxide, Fe2O3
3H2O. Acidification shifts the equilibrium, causing a greater release of Fe3þ as
a solution ion.
In addition to deficiency of some micronutrients, overliming can also
create problems of Al toxicity. Aluminum solubility is minimal in the pH
range of 5.5–6.5 (Haynes, 1984). At higher pH values, Al becomes increasingly soluble as the negatively charged aluminate form. Farina et al. (1980)
reported increased uptake of Al by corn (Zea mays L.) at near neutral pH
values and such Al uptake decreased corn yield. This type of detrimental
effect of Al can occur at pH higher than 7.0 in water and liming of Oxisols
around pH 6.5 in water can produce maximum yields of most food crops
(Fageria et al., 1997).
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Table 8
Influence of soil pH on micronutrient concentrations in soil and plant uptake
Micronutrient
Influence on concentration/uptake
Zinc
Zinc solubility is highly soil pH dependent and decreases
100-fold for each increase in pH, and uptake by plant
decreases as a consequence.
Iron
Ferric (Fe3þ) and ferrous (Fe2þ) activities in soil solution
decrease 1000-fold and 100-fold, respectively, for each unit
increase in soil pH. In most oxidized soils, uptake of Fe by
crop plants decreases with increasing soil pH.
Manganese
The principal ionic Mn species in soil solution is Mn2þ, and
concentrations decrease 100-fold for each unit increase in
soil pH. In extremely acidic soils, Mn2þ solubility can be
sufficiently high to induce toxicity problems in sensitive
crop species.
Copper
Solubility of Cu2þ is very soil pH dependent and decreases
100-fold for each unit increase in pH. Plant uptake also
decreases.
Boron
Sorption of B to Fe and Al oxides is pH dependent and is
highest at pH 6.0–9.0. Bioaavailability of B is higher
between pH 5.5 and 7.5, decreasing below and above this
range mainly due to pH-dependent reactions.
Molybdenum Above soil pH 4.2, MoO42 is dominant. Concentration of
these species increases with increasing soil pH and plant
uptake also increases. Water-soluble Mo increases sixfold as
pH increases from 4.7 to 7.5. Replacement of adsorbed Mo
by OH is responsible for increases in water-soluble Mo as
soil pH increases.
Chlorine
Chloride is bound tightly by most soils in mildly acidic to
neutral pH soils and becomes negligible to pH 7.0.
Appreciable amounts can be adsorbed with increasing soil
acidity.
Source: Adriano (1986), Fageria et al. (1997, 2002), Mortvedt (2000), and Tisdale et al. (1985).
5. Factors Affecting Lime Requirements
Lime requirement is defined as the amount of liming material,
as calcium carbonate equivalent, required to change a volume of soil to
a specific state with respect to pH or soluble Al content (Soil Science Society
of America, 1997). However, in economic terms, lime requirement can be
defined as the quantity of liming material required to produce maximum
economic yield of crops cultivated on acid soils. Quantity of lime required to
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Table 9 Influence of soil pH on acquisition of Zn, Cu, Fe, and Mn by upland rice grown
in an Oxisol of Brazil
Soil pH
Zn
(mg plant1)
Cu
(mg plant1)
Fe
(mg plant1)
Mn
(mg plant1)
4.6
5.7
6.2
6.4
6.6
6.8
R2
1090
300
242
262
163
142
0.98**
75
105
78
64
61
51
0.89*
4540
1860
1980
1630
1660
1570
0.97**
11,160
5010
4310
3610
2760
2360
0.99**
*,** Significant at 5 and 1% probability levels, respectively.
Source: Fageria (2000).
Table 10 Influence of soil pH on shoot dry weight, grain yield, and panicle number of
upland rice grown on Oxisols
pH in H2O
Shoot dry
weight (g plant1)
Grain yield
(g plant1)
Panicle number
(plant1)
4.6
5.7
6.2
6.4
6.6
6.8
R2
15.9
14.9
12.2
10.6
7.8
6.0
0.99**
11.0
11.5
11.7
9.5
6.8
5.2
0.91**
5.0
4.6
4.5
3.9
3.4
3.3
0.94**
** Significant at the 1% probability level.
Source: Fageria (2000).
produce maximum economic yields of crops grown on acid soils is determined by soil properties, liming material quality, management practices,
cropping systems, crop species or genotypes within species, calcium and
magnesium interaction with other nutrients, and economic considerations.
5.1. Quality of liming material
Quality of liming material is very important in correcting soil acidity.
Chemical analysis of the liming material gives its composition. A liming
material containing both calcium and magnesium is desirable for correcting
soil acidity and improving contents of Ca and Mg of the soil. Two important characteristics that determine lime material quality are its neutralizing
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power or reactivity and fineness. The chemical effectiveness of agricultural
limestone is measured by its CaCO3 equivalence. If neutralizing value is
lower than CaCO3, a higher quantity of liming material is required and
vice a versa. The neutralizing power or value of a liming material is defined
as the acid-neutralizing capacity of the material by weight in relation to
CaCO3. A dolomitic limestone has a higher neutralizing capacity than a
calcitic limestone because of the lower atomic weight of Mg. Pure dolomite
has a CaCO3 equivalence of 1.08 (Barber, 1984). Table 11 shows various
liming materials and their CaCO3 equivalent values (neutralizing values).
The degree of fineness indicates the speed with which lime materials will
neutralize soil acidity. Fineness is measured by the proportion of processed
agricultural lime which passes through a sieve with an opening of a particular size. A 60-mesh sieve, which is the standard for comparisons of lime
finesse and efficiency rating of 100%, is assigned (Caudle, 1991).
5.2. Soil texture
The relative proportions of sand, silt, and clay in a given soil determine soil
texture, a basic physical property of the soil that remains unchanged by
cultural and management practices. The sand group includes all soils whose
Table 11 Liming materials, their composition, and neutralizing power
Commercial
name
Chemical
formula
Neutralizing
value (%)
Dolomitic
lime
CaMg(CO3)2
95–109
Calcitic lime
CaCO3
100
Dolomite lime
MgCO3
100–120
Burned lime
CaO
179
Slaked lime
Ca(OH)2
136
Basic slag
CaSiO3
86
Wood ash
Variable
30–70
Characteristics
Contains 78–120
g kg1 of Mg and
180–210 g kg1
of Ca
Contains 284–320
g kg1 of Ca
Contains 36–72
g kg1 of Mg
Fast reacting and
difficult to handle
Fast reacting and
difficult to handle
Byproduct of pig-iron
industry, also
contains 1–7% P
Caustic and water
soluble
Source: Fageria (1989), Bolan et al., (2003), Brady and Weil (2002), and Caudle (1991).
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sand content by weight is 85% or more, the silt group has a silt content of
80% or more, and the clay group includes those whose clay content is 40%
or more (Soil Science Society of America, 1997). Soil texture determines
the buffering capacity of a soil, which refers to the ability of the solid phase
soil materials to resist changes in ion concentrations in the solution phase.
For liming purposes, the resistance of the soil solution to changes in pH is a
main component of soil buffer power. Oxisols contain predominantly iron
and aluminum oxide minerals and kaolinite and have characteristically low
to moderately low cation exchange capacity, but they also have high
buffering capacity. Hence, Oxisols require large amount of liming materials
to raise soil pH to a desired level for maximum crop yields. Maximum
legume grain yield (common bean, soybean) is achieved at a pH of about 6.5
in Brazilian Oxisols (Fageria, 2001b, 2006; Fageria and Stone, 2004). Data
in Fig. 2 show that to raise a pH from 5.3 to 6.5 in Oxisols, a lime rate of
about 7 Mg ha1 is needed.
5.3. Soil fertility
Soil fertility has a significant influence on the quantity of lime required to
correct soil acidity to produce maximum economic crop yields. Quantity of
nutrient present in the soil is defined in term of soil fertility, and, generally,
soil analysis is used as a criterion to make fertilizer recommendations for
Soil pH in H2O
7.0
6.5
6.0
Y = 5.2809 + 0.2181X - 0.0061X 2
R 2 = 0.9656**
5.5
5.0
0
3
6
9
12
15
18
Lime applied (Mg ha-1)
Figure 2
Relationship between lime rate and soil pH in Brazilian Oxisols.
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Table 12 Influence of liming on base saturation and exchangeable Caþ and Mg2þ at
0–20 cm depth in an Oxisols
Lime rate
(Mg ha1)
Base saturation
(%)
Ca2þ
(cmolc kg)
Mg
(cmolc kg1)
0
4
8
12
16
20
R2
40
44
51
53
56
66
0.80**
1.9
2.3
3.0
3.1
3.3
3.8
0.72**
1.0
1.1
1.2
1.3
1.3
1.4
0.23*
*,** Significant at the 5 and 1% probability level, respectively.
Source: Fageria (2001a,b).
field crops (Fageria and Baligar, 2005b). High fertility soils in terms of
exchangeable Ca2þ, Mg2þ, and Kþ require less lime than do those with
lower soil fertility. When Ca2þ, Mg2þ, and Kþ contents are higher, a lower
lime rate is required, because of higher levels of these basic cations in the
soil, meaning relatively higher base saturation and higher pH than with
lower levels of these cations (Table 12).
5.4. Crop rotation
Crop rotation is defined as a planned sequence of crops growing in a regularly
recurring succession on the same area of land, as contrasted to continuous
culture of one crop or growing a variable sequence of crops (Soil Science
Society of America, 1997). This is a very old system of growing crops and was
practiced during the Han dynasty of China more than 3000 years ago (Karlen
et al., 1994; MacRae and Meheys, 1985). Romans recognized the benefits of
alternating leguminous crops with cereals more than 2000 years ago (Karlen
et al., 1994; Robson et al., 2002). Continuous cultivation of a given crop on
the same land may reduce productivity. This decline in productivity is
associated with a decrease in soil fertility, infestation by weeds, insects, and
diseases, loss of soil by erosion, reduction in soil biological diversity, and
buildup of allelopathy (Fageria, 2002). Ability of legumes to fix atmospheric
nitrogen discovered in the late 19th century was a major reason for crop
rotation (cereals with legumes) that became popular in the early 20th century
(Karlen et al., 1994).
Crop rotation has several benefits. Diversifying crops in rotation can
improve crop yields, a response known as the rotation effect (Anderson,
2003). Phosphorus deficiency or unavailability is a major yield-limiting
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369
factor in Oxisols, and in the Central Great Plains of the United States, crop
rotations have been reported to improve P-use efficiency (Bowman and
Halvorson, 1997). However, there are some disadvantages in adopting crop
rotation. One such disadvantage is soil acidification, a serious form of land
degradation associated with crop rotation (Coventry et al., 2003). In crop
rotations, the N cycle and C cycle contribute most to the acid input
(Coventry and Slattery, 1991; Helyar et al., 1997). Acidification of soil
can also result from increasing addition of crop residues due to crop rotation
(Poss et al., 1995). It is reported in several studies in southern Australia that
in the wheat-based crop rotation, the rates of acidification can be 0.16–3.6
Hþ ha1 year1 for pastures (Loss et al., 1993; Ridley et al., 1990) and
1.0–7.5 Hþ ha1 year1 for cereal–legume rotations (Coventry and Slattery,
1991; Dolling, 1995; Moody and Aitken, 1997). The rate of acidification in
intensive cropping systems is also associated with removal of large amounts of
calcium and magnesium in the grains. In addition, acidification in the tropical
rainforest such as the cerrado region of Brazil is also associated with the
replacement of perennial vegetation with shallow-rooted annual pastures
and crops. With this change, more water has drained through the soil profile,
which leads to removal of bases (Coventry et al., 2003). The rates of acidification are generally more pronounced in higher rainfall areas and soil pH
in the range of 4.8–5.5 (CaCl2) is likely to be more susceptible to rapid
acidification (Coventry et al., 2003; Haynes, 1983).
5.5. Use of organic manures
Organic manures are products from the processing of animal or vegetable
substances that contain reasonable amount of plant nutrients to be of value
as fertilizers. Brosius et al. (1998) reported that plant- and animal-based
organic byproducts may substitute for commercial fertilizers and enhance
chemical and biological attributes of soil quality in agricultural production
systems. Use of organic manures can also affect lime requirement of a crop.
Organic matter increases the soil’s ability to hold and make available
essential plant nutrients and to resist the natural tendency of soil to become
acidic (Cole et al., 1987). Furthermore, addition of organic manures to acid
soils has been shown to increase soil pH, decrease Al saturation, and thereby
improve conditions for plant growth (Alter and Mitchell, 1992; Reis and
Rodella, 2002; Wong and Swift, 2003). Miyazawa et al. (1993) reported that
crop residues of wheat and corn and 20 plant species utilized as green
manure increased soil pH and decreased Al content of the soil. Several
mechanisms have been proposed for reducing acidity by organic manures.
These mechanisms include specific adsorption of organic anions on hydrous
Fe and Al surfaces and the corresponding release of hydroxyl ions which
increase soil pH (Hue, 1992; Wong and Swift, 2003). Adsorption of Al by
organic matter sites and the subsequent isolation of the inorganic phase to
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N. K. Fageria and V. C. Baligar
maintain the equilibrium Al activity in soil solution have been proposed to
increase soil pH (Wong and Swift, 2003; Wong et al., 1998). Chelating
agents released by decomposing organic matter may detoxify Al ions.
Plant roots decay in the soil and form into soil organic matter. Active roots
also release organic acids such as citrate, malate, and tartrate. These organic
acids react strongly with Al and convert it into less toxic organically bound
forms (Yang et al., 2000). The organic Al affinities or stability constants are in
the order of citrate > tartrate > malate (Hue et al., 1986). The decrease in
Al-activity by addition of organic matter has been reported by Kochain
(1995). The functional groups involved in metal complexation by organic
matter are COOH and OH (Wong and Swift, 2003). Surface application or
surface incorporation of organic matter also decreased phytotoxic subsoil
Al3þ activities because dissolved organic matter (DOM) that leached into
the subsoil formed nontoxic Al–DOM complexes (Hue, 1992; Hue and
Licudine, 1999; Liu and Hue, 1996; Willert and Stehouwer, 2003). The
combined application of CaCO3 and organic matter in lime-stabilized biosolids decreased subsoil acidity and increased subsoil Ca saturation, compared
with CaCO3 alone (Brown et al., 1997; Tan et al., 1985; Tester, 1990; Willert
and Stehouwer, 2003). This effect was attributed to increases in Ca mobility
caused by Ca–DOM complexes (Willert and Stehouwer, 2003).
Additional benefits of organic matter addition to acid soils are improving
nutrient cycling and availability to plants through direct additions as well as
through modification in soils’ physical and biological properties. A complementary use of organic manures and chemical fertilizers has proven to be the
best soil fertility management strategy in the tropics (Fageria and Baligar,
2005a; Makinde and Agboola, 2002). Enhanced soil organic matter increases
soil aggregation and water-holding capacity, provides source of nutrients, and
reduces P fixation, toxicities of Al and Mn, and leaching of nutrients (Baligar
and Fageria, 1999). Build-up of organic matter through additions of crop and
animal residues increases the population and species diversity of microorganisms and their associated enzyme activities and respiration rates (Kirchner
et al., 1993; Weil et al., 1993). The use of organic compost may result in a soil
that has greater capacity to resist the spread of plant pathogenic organisms.
The improvement in overall soil quality may produce more vigorous
growing and high yielding crops (Brosius et al., 1998).
5.6. Conservation tillage
The mechanical manipulation of the soil profile for crop production is
known as tillage. Conservation tillage is minimum manipulation of the
soil profile for crop production and 30% or more soil surface is covered
with crop residues. In conservation tillage, weeds are controlled by herbicides and this practice helps in conservation of water and nutrients, and
reduces soil erosion and labor cost. Conservation tillage reduces oxidation
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of organic matter or conserves soil organic matter content and consequently
decreases the adverse effects of soil acidity. Additional research is needed to
assess the long-term conservation tillage effects on soil acidity.
5.7. Crop species and genotypes within species
Crop species and genotypes within species differ significantly in relation to
their tolerance to soil acidity (Baligar and Fageria, 1997; Devine, 1976;
Fageria and Baligar, 2003b; Fageria et al., 1989, 2004; Foy, 1984; Garvin
and Carver, 2003; Reid, 1976; Sanchez and Salinas, 1981; Yang et al.,
2000). Hence, lime requirements also vary from species to species and
among cultivars within species. Many of the plant species tolerant to acidity
have their center of origin in acid soil regions, suggesting that adaptation to
soil constraints is part of the evolution processes (Foy, 1984; Sanchez and
Salinas, 1981). A typical example of this evolution is the acid soil tolerance
of Brazilian upland rice cultivars. In Brazilian Oxisols, upland rice grows
very well without liming, when other essential nutrients are supplied in
adequate amount and water is not a limiting factor (Fageria, 2000, 2001a).
Experimental results obtained on Brazilian Oxisols with upland rice are
good examples of crop acidity tolerance evaluation. Fageria et al. (2004)
reported that grain yield and yield components of 20 upland rice genotypes
were significantly decreased at low soil acidity (limed to pH 6.4) as compared
with high soil acidity (without lime, pH 4.5), demonstrating the tolerance of
upland rice genotypes to soil acidity. In Table 13, data are presented showing
grain yield and panicle number of six upland rice genotypes at two acidity
levels. These authors also reported that grain yield gave significant negative
correlations with soil pH, Ca saturation, and base saturation. Further, grain
Table 13 Grain yield and panicle number of six upland rice genotypes at two soil
acidity levels in Brazilian Oxisols
Grain yield (g pot1)
Panicle number (pot1)
Genotype
High acidity
(pH 4.5)
Low acidity
(pH 6.4)
High acidity
(pH 4.5)
Low acidity
(pH 6.4)
CRO97505
CNAs8983
Primavera
Canastra
Bonança
Carisma
Average
74.3
55.2
53.0
51.6
48.8
50.8
66.7
52.0
42.9
47.2
38.9
36.5
17.5
47.0
38.0
29.0
25.0
32.0
26.3
43.3
38.7
28.3
25.7
21.7
26.3
20.7
17.7
28.1
Source: Compiled from Fageria et al. (2004).
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N. K. Fageria and V. C. Baligar
yield had significant positive correlations with soil Al and H þ Al, confirming
that upland rice genotypes were tolerant to soil acidity. Fageria (1989)
reported stimulation of growth of Brazilian rice cultivars at 10 mg Al3þ L1
in nutrient solution compared with a control (no Al) treatment. Okada and
Fischer (2001) suggested that the mechanism for the genotype difference of
upland rice for tolerance to soil acidity is due to the relationship between
regulation of cell elongation and legend-bound Ca at the root apoplast.
A substantial number of plant species of economic importance are
generally regarded as tolerant to acid soil conditions of the tropics
(Sanchez and Salinas, 1981). In addition, there are cultivars within crop
species that are tolerant to soil acidity (Fageria et al., 2004; Garvin and
Carver, 2003; Yang et al., 2004). Yang et al. (2005) reported significant
differences among genotypes of rye, triticale, wheat, and buckwheat to Al
toxicity. These crop species or cultivars within these species can be planted
on tropical acid soils in combination with reduced rates of lime input.
Combination of legume–grass pasture and agroforestry system of management are the other important soil acidity management components
useful in tropical ecosystems. For example, Pueraria phaseoloides is used as
understory for rubber, Gmelina arborea or Dalbergia nigra, plantations in
Brazil, presumably supplying nitrogen to the tree crops (Sanchez and
Salinas, 1981) A detailed discussion of combination of legume–grass pasture
and agroforestry in tropical America is given by Sanchez and Salinas (1981).
These authors reported that when an acid-tolerant legume or legume–grass
pasture is grown under young tree crops, the soil is better protected, soil
erosion is significantly reduced, and nutrient cycling is enhanced. Some
important annual food crops, cover or green manure crops pasture species,
and plantation crops tolerant to tropical acid soils are listed in Table 14. Acid
soil tolerant crops are useful to establish low input management systems.
5.8. Interaction of lime with other nutrients
Recognition of the importance of nutrient balance in crop production is an
indirect reflection of the contribution of interactions to yield. The highest
yields are obtained where nutrients and other growth factors are in a
favorable state of balance. As one moves away from this state of balance,
nutrient antagonisms are reflected in reduced yields (Fageria et al., 1997).
Nutrient interactions can occur at the root surface or within the plant and
can be classified into two major categories. In the first category are interactions which occur between ions because the ions are able to form a chemical
bond. Interactions in this case are due to formation of precipitates or
complexes either in soil or in the plant. For example, this type of interaction
occurs where the liming of acid soils decreases the concentration of almost
all micronutrients in soil solution except molybdenum. Such reduction in
ion concentration in soil solution decreases the uptake. Increasing soil pH
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Table 14 Some important crop species, pasture species, and plantation crops tolerant
to soil acidity in the tropics
Annual crop species
Pasture species
Plantation crops
Rice
Peanut
Cowpea
Potato
Cassava
Pigeon pea
Millet
Kudzu
Mucuna
Crotolaria
Brachiaria
Andropogon
Panicum
Digitaria
Napiergrass
Jaraguagrass
Centrosema
Stylosanthes
Banana
Oil palm
Rubber
Coconut
Cashewnut
Coffee
Guarana
Tea
Leucaena
Brazilian nut
Eucalyptus
Papaya
Source: Sanchez and Salinas (1981), Caudle (1991), Fageria et al. (1997), and Brady and Weil (2002).
due to lime will have a more marked effect on Zn than Cu uptake, mainly
because Cu is more complexed and protected from precipitation by soluble
organic matter (Robson and Pitman, 1983). The second form of interaction
is between ions whose chemical properties are sufficiently similar that they
compete for site of adsorption (soil components, cell walls), absorption,
transport, and function on plant root surfaces or within plant tissues. Such
interactions are more common between nutrients of similar size, charge,
geometry of coordination, and electronic configuration (Robson and
Pitman, 1983).
Generally, three types of interactions occur among essential nutrients in
plants, and these interactions are known as synergistic, antagonistic, and
neutral. If upon addition of two nutrients, an increase in plant growth or
yield that is greater than that achieved by adding only one occurs, the
interaction is synergistic or positive. Similarly, if adding the two nutrients
together produced less plant growth or yield as compared to individual
ones, the interaction is negative or antagonistic. When there is no significant
change in plant growth or yield with the addition of two nutrients, there is
no interaction (Sumner and Farina, 1986). Data in Table 15 show that lime
and P fertilization have positive as well as negative interactions depending
on crop species. In the case of upland rice and wheat, shoot dry weight
yields were higher at zero level of lime compared with 2 and 4 g lime kg1
of soil. Hence, interaction between lime and P in this case was negative.
Whereas, shoot dry matter yield of common bean and corn increased with
increasing lime as well as P rates, indicating that interaction between lime
and P in this case was synergistic. An increasing response to applied P with
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N. K. Fageria and V. C. Baligar
Table 15 Dry matter yield of shoots of upland rice, wheat, common bean, and corn as
affected by lime and phosphorus applied to a Brazilian Oxisols
Lime rate
(g kg1)
P rate
(mg kg1)
Rice
(g pot1)
Wheat
(g pot1)
Common
bean
(g pot1)
Corn
(g pot1)
0
0
0
2
2
2
4
4
4
0
50
175
0
50
175
0
50
175
0.72
15.08
18.63
0.73
15.23
13.23
0.33
10.20
13.20
0.17
5.83
8.40
0.20
5.20
6.50
0.20
4.90
5.97
1.25
8.30
10.60
1.30
9.00
10.60
1.70
10.50
12.00
1.10
4.93
8.73
1.43
7.13
11.47
1.10
6.60
9.93
Source: Compiled from Fageria et al. (1995).
increasing rates of added lime has been attributed to either an improved rate
of supply of P by the soil or an improved ability of the plant to absorb P
when Al toxicity has been eliminated (Friesen et al., 1980b). Liming also
improves the microbiological activities of acid soils, which, in turn, can
increase dinitrogen fixation by legumes and liberate N and other nutrients
from incorporated organic materials (Fageria et al., 1995).
Nutrient interaction is also evaluated by studying the influence of
increasing nutrient concentrations on the uptake of other nutrients and
corresponding plant growth. When plant uptake of a given nutrient
decreased and corresponding plant growth also decreased, interaction is
negative. However, if plant growth and nutrient concentration increased
with increasing nutrient supply, the interaction is positive.
Liming of acid soils is mainly to supply Ca and Mg to plants and
neutralize phytotoxic levels of soil Al3þ. Hence, interaction of Ca2þ,
Mg2þ, and Al3þ with other elements is an important aspect for nutrient
interaction discussion. Although absolute Ca requirements for plant growth
and metabolism are low, it has great significance in providing balance for
levels of other plant nutrients, maintaining membrane integrity, and reducing potential for toxicity of other elements (Wilkinson et al., 2000). Potassium, Al3þ, Mg2þ, Mn2þ, and Hþ and heavy metals can reduce Ca uptake
by binding at the exterior surface of plasma membrane which increases the
Ca requirement (Marschner, 1995). Fertilization with NO3 generally
enhances Ca and Mg concentrations in plants driven by the need for
cation–anion balance (Wilkinson et al., 2000). Lime and P interactions are
mainly associated with Al toxicity, which limits root growth and proliferation, and nutrient uptake. Aluminum absorbed by roots can also precipitate
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375
root-absorbed P and hinder its subsequent translocation to plant tops (Foy,
1983). Mora et al. (2005) reported that the most important Al detoxifying
mechanisms in ryegrass were apparently physiological Al-PO4 precipitation
inside the root and chemical AlSOþ
4 complex formation in the nutrient
solution.
The results of solution culture experiments have shown that negative
effects of Al on root growth can be reduced by increasing Ca2þ concentration in the growth medium (Nichol et al., 1993; Zysset et al., 1996). Baligar
et al. (1992) also reported that Ca ameliorates Al toxicity in wheat plants.
Huang and Grunes (1992) reported that adequate supply of Ca and Mg might
also ameliorate Al toxicity in wheat plants. Aluminum toxicity continues to
be associated with P nutrition of plants (Foy, 1984). Santana and Braga
(1977) found that P concentrations in rice tops decreased with increasing
Al saturation of the soil. Helyar (1978) concluded that Al toxicity effects
were largely associated with Al interference with P metabolism and with Al
binding to pectins in root cell wall, stopping root elongation. Fageria and
Baligar (1999) studied the interactions between calcium and P, Mg, Zn, Cu,
Mn, Fe, and B in common bean and found that uptake of P was quadratically
increased, whereas uptake of Mg, Zn, Cu, Mn, Fe, and B significantly
decreased as soil Ca increased from 4.9 to 12.5 cmolc kg1 of soil.
Calcium Al3þ interactions are important in acid soils (Foy, 1984).
Below pH 5.5, Ca2þ Al3þ antagonism is probably the most important
factor affecting Ca uptake by plants. Lance and Pearson (1969) reported that
reduced Ca uptake was the first externally observed symptom of Al damage
on cotton seedlings. Franco and Munns (1982) reported that increasing
Ca2þ concentrations from 8 to 80 mg L1 decreased Al toxicity in bean
plants. Simpson et al. (1977) attributed poor root growth of alfalfa to Al3þ Ca2þ interaction. Aluminum Feþ3 interactions are frequently reported in
the literature (Foy, 1984). Alam (1981) reported Al-induced Fe deficiency
in oat and postulated that Al interfered with the reduction of Fe3þ to Fe2þ
within the plant, a process essential for normal Fe metabolism and utilization. Clark et al. (1981) found that Fe-deficiency chlorosis was a common
symptom of Al toxicity in sorghum.
6. Criteria to Determine Liming
Material Quantity
Use of adequate lime rate to correct soil acidity and production of
maximum yield of a crop species is an important consideration for economical and ecological reasons. Quantity of liming material required is determined on the basis of soil pH, base saturation, and aluminum saturation
adjustment at appropriate levels. Appropriate levels of these acidity indices
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N. K. Fageria and V. C. Baligar
vary with soil type, soil fertility, plant species, and crop genotypes within
species (Fageria and Baligar, 2003a). In addition, crop response
curves related to lime rate and yield is another criterion that can be used
to define lime requirement for any given crop species. Crop response curves
to lime levels should be determined for each crop species under different
agroecological regions to make liming recommendations effective and
economical.
6.1. Soil pH
Soil pH or hydrogen ion activity is the most common acidity index used
in soil testing program for assessing lime requirements of crops grown on acid
soils. Weaver et al. (2004) reported that soil pH buffering capacity, since it
varies spatially within crop production fields, may be used to define sampling
zones to assess lime requirement, or for modeling changes in soil pH when
acid-forming fertilizers or manures are added to a field. The pH is defined as
the negative logarithm of the hydrogen ion concentration or activity. It is
determined by means of a glass, quinhydrone, or other suitable electrode or
indicator at a specified soil to solution ratio in a specified solution, usually
distilled water, 0.01 M CaCl2, or 1 M KCl (Soil Science Society of America,
1997). In soil testing laboratories of Brazil, a soil to solution ratio of 1:2.5 is
commonly used to determine soil pH (EMBRAPA, 1997).
The pH measured in the soil solution represents the active acidity of the
soil. Hydrogen and aluminum ions adsorbed by the soil, as well as other soil
constituents that generate hydrogen ions, constitute the reserve acidity. The
active acidity is neutralized by the addition of lime where more hydrogen ions
from the reserve pool go into solution. This results in the resistance of soil to
changes in the pH of the soil solution. This is termed ‘‘buffering capacity.’’
The pH of acid soils is lower than 7.0, that of neutral soils is equal to 7.0,
and that of alkaline soils is above 7.0. At neutrality, the concentrations of
OH ions and Hþ ions are equal, since these ions are derived in equal
quantities from the ionization of water. The pH of most agricultural soils is
in the range of 4.0–9.0 (Fageria et al., 1990, 1997). Soil acidity is classified
into several groups based on soil pH. Slightly acid soils have a pH range of
6.0–7.0, moderately acid soils pH range from 5.5 to 6.0, strongly acid soils
pH from 4.5 to 5.0, and extremely acid soils have a pH range below 4.5
(Fageria and Gheyi, 1999). These acidity classifications are arbitrary, and
care should be taken when defining adequate pH for crop yields, particularly the extractant used could make a difference. Soil pH in water is higher
than that in CaCl2 solution.
Soil pH measurements not only indicate the acidity level of a soil but also
be used as an initial basis for the prediction of the chemical behavior of soils,
particularly in relation to nutrient availability and the presence of toxic
elements. Most plant-essential nutrients in soil reach maximal or near-maximal
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availability in the pH range 6.0–7.0, and decrease both above and below this
range (McLean, 1973). Optimal pH values for annual crops cultivated on
Brazilian Oxisols are given in Table 16. A curve showing the relationship
between lime rate and pH change of a Brazilian Oxisol is presented in Fig. 2.
Oxisols with application of lime 0–18 Mg ha1 increase pH significantly and
quadratically. Figure 3 shows the relationship between pH of an Oxisol and
shoots dry weight and grain yield of common bean. Maximum shoot dry
weight and grain yields were obtained at a pH of 6.4. Improvement in grain
yield was associated with increasing numbers of pods, grains per pod, and
weight of 100 seeds when pH was increased from 5.3 to 6.4 (Fig. 4).
6.2. Base saturation
Base saturation is another important chemical property of soils used as a
criterion for liming recommendations. Base saturation is defined as the
proportion of the CEC occupied by exchangeable bases. It is calculated as
follows (Fageria et al., 2007):
Table 16
Optimal soil pH for important crop species grown on Brazilian Oxisols
Crop species
Wheat
Common
bean
Upland rice
Type of
experiment
Plant part
measured
Soil pH in
H2O (1:2.5) Reference
Greenhouse Shoot dry 6.0
weight
Field
Grain yield 6.6
Field
Grain yield 5.6
Common
bean
Corn
Soybean
Upland rice
Field
Grain yield 6.2
Field
Field
Field
Grain yield 6.4
Grain yield 6.8
Grain yield 5.5
Upland rice
Upland rice
Greenhouse Grain yield 5.4
Greenhouse Grain yield 5.9
Corn
Field
Grain yield 6.2
Soybean
Field
Grain yield 6.4
Fageria et al.
(1997)
Fageria and Stone
(2004)
Fageria and
Baligar (2001)
Fageria and
Baligar (2001)
Fageria (2001b)
Fageria (2001b)
Fageria and Stone
(1999)
Fageria (2000)
Fageria et al.
(1990)
Gonzales-Erico
et al. (1979)
Raij and Quaggio
(1997)
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N. K. Fageria and V. C. Baligar
Shoot dry weight and grain yield (kg ha−1)
Shoot
Grain
a
a
6.4
6.8
3000
b
2000
a
a
b
1000
0
5.3
6.4
6.8
5.3
Soil pH in H2O
Figure 3 Relationship between soil pH and shoot dry weight and grain yield of
common bean grown on a Brazilian Oxisol (Fageria and Santos, 2005).
b
200
100
4
a
c
b
Weight of 100 grains (g)
Number of pods (m−2)
a
Number of grains (pod−1)
a
300
3
2
1
a
a
6.4
6.8
b
30
20
10
0
5.3
6.4
6.8
5.3
6.4
6.8
5.3
Soil pH in H2O
Figure 4 Relationship between soil pH and yield components of common bean grown
on Brazilian Oxisols (Fageria and Santos, 2005).
P
Base saturationð%Þ ¼
ðCa; Mg; K; NaÞ
100
CEC
where CEC is the sum of Ca, Mg, K, Na, H, and Al expressed in cmolc
kg1.
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In Brazil, Naþ is generally not determined because of a very low level of
this element in Brazilian Oxisols (Raij, 1991). Hence, Na is not considered
in the calculation of CEC or base saturation.
For crop production, base saturation levels in soil may be grouped into
very low (lower than 25%), low (25–50%), medium (50–75%), and high
(>75%) (Fageria and Gheyi, 1999). Very low and low base saturation means
a predominance of adsorbed hydrogen and aluminum on the exchange
complex. Deficiencies of calcium, magnesium, and potassium are likely to
occur in soils with low CEC and very low to low percent base saturation.
Quantity of lime required by the base saturation method is calculated by
using the following formula (Fageria et al., 1990):
CECðB2 B1 Þ
df
Lime rateðMg ha Þ ¼
TRNP
1
where CEC: cation exchange capacity or total exchangeable cations (Ca2þ,
Mg2þ, Kþ, Hþ þ Al3þ) in cmolc kg1, B2: desired optimum base saturation, B1: existing base saturation, TRNP: total relative neutralizing power
of liming material, and df: depth factor, 1 for 20 cm depth and 1.5 for 30 cm
depth.
For Brazilian Oxisols, the desired optimum base saturation for most of
the cereals is in the range of 50–60%, and for legumes it is in the range of
60–70% (Fageria et al., 1990). However, there may be exceptions, like
upland rice, which is very tolerant to soil acidity and can produce good
yield at base saturation lower than 50%. Specific optimal base saturation
values for important annual crops grown on Brazilian Oxisols are given in
Table 17. Nature of the soil alters the optimum base saturation required by
any given crop species. A relationship between lime rate and base saturation
in a Brazilian Oxisol is given in Fig. 5. Bean yield was having significant
quadratic response in relation to base saturation (Fig. 6). Maximum yield
was obtained with base saturation of 73% at 0–10 cm soil depth, with base
saturation of 62% at 10–20 cm soil depth and at 67% base saturation when
averaged across two soil depths. Hence, at topsoil layer, higher base saturation
was required compared with that at lower soil layer (Fageria, 2008).
6.3. Exchangeable aluminum, calcium, and magnesium levels
Aluminum has long been recognized as a toxic element for plant growth
(Cronan and Grigal, 1995; Foy, 1984). In soil–plant systems, plant-available
Al is determined by soil extraction procedure to predict the risk of Al
toxicity and the need for liming (Thomas and Hargrove, 1984). In addition,
Ca and Mg contents of the Oxisols are important in determining growth of
plants. Hence, exchangeable aluminum, calcium, and magnesium contents
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N. K. Fageria and V. C. Baligar
Table 17 Optimal base saturation for important annual crops grown on Brazilian
Oxisols
Type of
experiment
Plant part
measured
Common
bean
Common
bean
Upland rice
Field
Grain yield 60
Field
Grain yield 69
Field
Grain yield 40
Common
bean
Corn
Soybean
Upland rice
Upland rice
Common
bean
Corn
Wheat
Soybean
Cotton
Sugarcane
Soybean
Field
Grain yield 70
Field
Field
Field
Field
Field
Grain yield
Grain yield
Grain yield
Grain yield
Grain yield
59
63
50
30
71
Field
Field
Field
Field
Field
Field
Grain yield
Grain yield
Grain yield
Grain yield
Cane yield
Grain yield
60
60
60
60
50
61
Crop species
Base
saturation (%)
Reference
Fageria and Santos
(2005)
Fageria and Stone
(2004)
Fageria and
Baligar (2001)
Lopes et al. (1991)
Fageria (2001a)
Fageria (2001a)
Lopes et al. (1991)
Sousa et al. (1996)
Fageria and Stone
(2004)
Raij et al. (1985)
Lopes et al. (1991)
Raij et al. (1985)
Raij et al. (1985)
Raij et al. (1985)
Gallo et al. (1986)
of the soil are taken into account to determine the rate of lime required for
a crop grown on an Oxisol. The equation used for lime rate determination
is (Fageria et al., 1990; Raij, 1991):
Lime rateðMg ha1 Þ ¼ ð2 Al3þ Þ þ ½2 ðCa2þ þ Mgþ Þ
where values of Al3þ, Ca2þ, and Mg2þ are expressed in cmolc kg1.
If values of Ca2þ and Mg2þ cations are more than 2 cmolc kg1, only Al
multiplied by factor 2 is considered. This criterion was originally suggested
by Kamprath (1970) for tropical soils and is still largely used for liming
recommendation for Brazilian acid soils (Paula et al., 1987; Raij, 1991; Raij
and Quaggio, 1997). Alvarez and Ribeiro (1999) recommended that the
factor used to multiply Al should be varied according to soil texture. These
authors suggested that in sandy soil with clay content of 0–15%, the factor
0–1 should be used; for medium-texture soils with clay content of 15–35%,
a factor 1–2 should be used; for clayey soil with clay content of 35–60%,
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Ameliorating Soil Acidity
100
Base saturation (%)
80
60
40
Y = 20.0658 + 8.1171X - 0.2493X 2
R 2 = 0.9635**
20
0
3
6
9
12
18
Lime rate (Mg ha-1)
Figure 5 Relationship between lime rate and base saturation of Brazilian Oxisols.
a factor 2–3 should be used; and for heavy clayey soil with clay content of
60–100%, a factor of 3–4 should be used.
6.4. Aluminum saturation
Crops grown in soils with acceptable levels of basic cations do not show Al
toxicity symptoms even when the levels of KCl-extractable Al are considered high (Kariuki et al., 2007). Hence, the mere presence of Al in the soil is
not an indicator of Al toxicity ( Johnson et al., 1997). A more reliable
measure of the potential for Al toxicity is Al saturation (Kariuki et al., 2007).
It has been widely reported in the literature that differences in Al tolerance
are found among plant species and cultivars within species (Fageria and
Baligar, 2003a; Foy, 1992; Kochain, 1995; Okada and Fischer, 2001; Yang
et al., 2004). It is evident, therefore, that crop tolerance to Al should be taken
into account in estimating the amounts of lime needed to correct Al toxicity.
Cochrane et al. (1980) suggested that crop aluminum tolerance should be
considered along with levels of exchangeable Ca and Mg, in determination of
lime requirement. Aluminum saturation, or the proportion of aluminum
among the cations, is calculated by using the following formula:
Al saturationð%Þ ¼
Al
100
ECEC
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N. K. Fageria and V. C. Baligar
Average of two
soil depths
3000
2000
Y = 1248.41 + 56.6337X - 0.4203X 2
R 2 = 0.7736**
1000
0
Grain yield (kg ha-1)
10–20 cm
3000
2000
Y = 1347.17 + 58.6230X - 0.4696X2
R2 = 0.7391**
1000
0
0–10 cm
3000
2000
Y = 1173.82 + 54.2814X - 0.3709X2
R2 = 0.7956**
1000
0
Figure 6
20
40
60
Base saturation (%)
80
Influence of base saturation on grain yield of dry bean (Fageria, 2008).
where ECEC is in cmolc kg1, which is the sum of exchangeable Al3þ,
Ca2þ, Mg2þ, and Kþ in cmolc kg1.
After determining Al saturation, the following formula is used to calculate lime rate (Cochrane et al., 1980):
3þ
Al TASðAl3þ þ Ca2þ þ Mg2þ Þ
Lime rateðMg ha Þ ¼ 1:8
100
1
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Ameliorating Soil Acidity
where 1 M KCL extracts Al, Ca, and Mg and concentrations are expressed
in cmolc kg1 and TAS is target Al saturation, which varied from crop
species to species.
Critical Al saturation values for important plant species are given in
Table 18. These values can be used as a reference guide to calculate
the lime rate for different crop species. This approach is very useful where
lime is difficult to obtain and rather costly and Al-tolerant cultivars are
available.
6.5. Crop responses
Methods discussed earlier for lime rate determination provide reference
guides for determination of lime rates for correcting soil acidity-related
constraints for crops. The best criterion, however, for determining lime
rate is actual testing of crop responses to applied lime rates. Crop responses
to liming are determined by soil, climate, plant species, and cultivar within
Table 18 Critical soil aluminum saturation for important field crops at 90–95% of
maximum yield
Crop
Type of soil
Critical Al
saturation (%)
Cassava
Upland rice
Cowpea
Cowpea
Peanut
Peanut
Soybean
Soybean
Soybean
Soybean
Corn
Corn
Corn
Corn
Mungbean
Mungbean
Coffee
Sorghum
Common bean
Common bean
Common bean
Cotton
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols
Oxisols/Ultisols
Oxisols
Oxisols
Oxisols
Oxisols/Ultisols
Not given
Oxisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Oxisols/Ultisols
Not given
80
70
55
42
65
54
19
27
15
<20
19
29
25
28
15
5
60
20
10
8–10
23
<10
Source: Compiled from various sources by Fageria et al. (1997).
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N. K. Fageria and V. C. Baligar
species and socioeconomic condition of growers and their interactions.
Hence, crop responses to liming should be determined in different agroecological regions.
Over the years in different region of Brazil, liming experiments have been
conducted on Oxisols with various annual crops. Lime rate to achieve 90% of
the maximum grain yield potential is considered an economic lime rate. Raij
and Quaggio (1997) reported that in the State of Sao Paulo, depending on
grain yield, economic optimum lime rate required for soybean is around 3.6–
5.5 Mg ha1. These authors also reported economic optimum lime rate of
6 Mg ha1 for cotton and 3.8 Mg ha1 for sugarcane. Fageria (2001a)
reported that for the State of Goiás, economic optimum lime rate was
5 Mg ha1 for common bean, 8 Mg ha1 for corn, and 9 Mg ha1 for
soybean. Caires et al. (2005) reported that in Brazilian Oxisols (Hapludox),
the maximum economic yield of wheat was obtained with application of
4 Mg ha1of lime. Figure 7 shows the relationship between lime rate and
grain yield of soybean grown on Brazilian Oxisols in the State of Tocantins.
Maximum grain yield was achieved at 12 Mg ha1 of lime. However, 90% of
the maximum yield (economical rate) was obtained with the application of
5.3 Mg ha1.
7. Methods, Frequency, Depth, and Timing
of Lime Application
Methods, frequency, depth, and timing of liming are important
practices in improving liming efficiency and crop yields on acid soils. Liming
material is applied in large quantity to bring about the desired chemical
Grain yield (kg ha-1)
3500
3000
2000
Y = 2205.7970 + 187.5253X - 7.7712X 2
R2 = 0.8688**
1000
0
3
6
9
12
15
18
Lime rate (Mg ha-1)
Figure 7 Relationship between lime rate and soybean grain yield grown on Brazilian
Oxisols.
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Ameliorating Soil Acidity
changes in acid soils. Hence, the best method is applying it as broadcast as
uniformly as possible and mixing thoroughly through the soil profile. Lime
broadcasting machines are available for uniform application of liming
materials.
Liming frequency is mainly determined by intensity of cropping, crop
species planted, and levels of Ca2þ, Mg2þ, Al, and pH in a soil after each
harvest. The effect of lime is long lasting but not permanent. After several
crops, Ca2þ and Mg2þ move downward and beyond the reach of roots.
These elements are taken up by crops and, to some extent, are lost through
soil erosion. Acid-forming fertilizers and decomposing organic matter lower
the soil pH and release more aluminum to the soil solution and cation
exchange sites on soil particles. When values of exchangeable Ca2þ, Mg2þ,
and pH fall below optimum levels for a given crop species, liming should be
repeated. This means that soil samples should be taken periodically to
determine changes in soil chemical properties and to decide liming frequency. Effects of lime do last longer than those of most other amendments;
however, it is rarely necessary to lime more frequently than every 3 years
(Caudle, 1991). Lime study on Oxisols of the cerrado region of Brazil
showed that after 4 years, with eight crops grown (two crops each year) in
rotation (rice, common bean, corn, and soybean), the soil maintained levels
of soil pH and Ca2þ and Mg2þ contents to maintain yields of these crops
at an optimal level (Table 19) (Fageria, 2001a). The residual effect of coarse
Table 19 Values of soil pH and Ca2þ and Mg2þ contents after harvest of eight crops
(upland rice, common bean, corn, and soybean) grown in rotation for 4 years on a
Brazilian Oxisol at two soil depths
Lime rate (Mg ha1)
0–20 cm soil depth
0
4
8
12
16
20
20–40 cm soil depth
0
4
8
12
16
20
Source: Fageria (2001a).
pH in H2O
Ca2þ
(cmolc kg1)
Mg2þ (cmolc kg1)
5.6
6.0
6.2
6.4
6.5
6.8
1.9
2.3
3.0
3.1
3.3
3.8
1.0
1.1
1.2
1.2
1.3
1.4
5.5
5.9
6.1
6.2
6.3
6.7
1.7
1.9
2.3
2.4
2.6
3.3
0.9
1.0
1.1
1.1
1.2
1.3
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N. K. Fageria and V. C. Baligar
lime material is greater than with finer lime material because large lime
particles react slowly with soil acidity and tend to remain in the soil longer.
Liming material should be mixed thoroughly in the soil as deeply as
possible to improve crop-rooting systems in acid soils. However, with
currently available machinery, it is generally mixed to a depth of 20–
30 cm. A depth greater than 30 cm required more powers and became
more costly in terms of labor and energy. Timing of lime application is
important in achieving desirable results. Lime should be applied as far in
advance as possible of planting of crop to allow it to react with soil colloids
and to bring about significant changes in soil chemical properties. Soil
moisture and temperature are determining factors for lime to react with
soil colloids. In Brazil, most of the published work shows that liming should
be done 3 months in advance of sowing a crop. However, other studies
carried at the National Rice and Bean Research Center have shown that in
Brazilian Oxisols significant chemical changes can take place 4–6 weeks
after applying liming materials if soil has sufficient moisture (Fageria, 1984,
2001a). Hence, to obtain desirable results, it is not necessary to wait for a
longer period of time after applying lime.
8. Conclusions
The increasing acidification of agricultural soils, as a result of natural
processes, industrial pollution, and agricultural practices, is adversely affecting crop production worldwide on significant levels. Highly weathered acid
soils cover about two-thirds of tropical America and are of great ecological
and economical importance. Soil order Oxisols make up the largest proportion of acid soils of this region. Soils of this order are acidic with low
fertility. Most soil acidity problems can be managed successfully, without
economic and environmental disruption. Among management factors for
acid soils, perhaps most important is supplying sufficient lime initially to
correct the majority of growth-limiting factors. Hence, adequate liming and
fertilization can reduce the adverse effects of soil acidity and improve crop
yields. The central part of Brazil, locally known as the cerrado region,
contains predominantly Oxisosls. Modern agricultural practices, including
liming and fertilization, could help to achieve economic yields on these
acidic and infertile soils. On these soils, the amount of lime needed for
maximum yield varies with crop species and cultivar within species. Experimental findings have shown that maximum economic yield for most annual
crops on Oxisols can be obtained with application of 4–6 Mg ha1 of lime.
Initially, liming acid soils not only improves crop yields but also helps to
maintain environmental quality and consequently improves animal and
human health. Overliming, however, can significantly reduce the
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Table 20
Common and scientific names of plant species cited in text
Common name
Crop species
Corn
Wheat
Soybean
Rice
Barley
Peanut
Cowpea
Potato
Cassava
Pigeon pea
Millet
Kudzu
Graybean
Triticale
Buckwheat
Rye
Crotolaria
Pasture species
(grasses and legumes)
Gambagrass or
Carimagua
Surinamgrass
Pangolagrass
Jaraguagrass
Paragrass
Guineagrass
Bahiagrass
Napiergrass
Desmodium
Brazilian stylo
Pueraria
Zornia
Plantation crops
Banana
Cashew
Coconut
Brazilian nut
Eucalyptus
Coffee
Rubber
Scientific name
Zea mays L.
Triticum aestivum L.
Glycimne max (L.) Merr.
Oryza sativa L.
Hordeum vulgare L.
Arachis hypogaea L.
Vigna unguiculata (L.) Walp.
Solanum tuberosum L.
Manihot esculenta Crantz
Cajanus cajan (L.) Millspaugh
Pennisetum glaucum (L.) R. Br.
Pueraria phaseoloides (Roxb.) Benth.
Mucuna cinerecum L.
X Triticosecale Wittmack
Fygopyrum esculentum Moench
Secale cereale L.
Crotolaria breviflora
Andropogon gayanus Kunth
Brachiaria decumbens Stapf.
Digitaria decumbens Stent
Hyparrhenia rufa (Nees) Stapf.
Brachiaria mutica (Forsk) Stafp.
Panicum maximum Jacq.
Paspalum notatum Fluegge
Pennisetum purpureum Schumach
Desmodium ovalifolium Guillemin & Perrottet
Stylosanthes guianiensis (Aubl.) Scv.
Pueraria phaseoloides Roxb.
Zornia latifolia
Musa paradisiaca L.
Anacardium occidentale
Cocos nucifera
Bertholletia excelsa
Eucalyptus grandiflora (Gaertn.) Hochr.
Coffea arabica L.
Hevea brasiliensis
(continued)
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N. K. Fageria and V. C. Baligar
Table 20 (continued)
Common name
Scientific name
Oil palm
Guarana
Tea
Papaya
Elaeis guineensis
Paullinia cupana
Cammellia Sinensis (L.) Ktze.
Carica papaya
bioavailability of micronutrients (Zn, Cu, Fe, Mn, B), which decreases with
increasing pH (Fageria et al., 2002). This can produce plant nutrient
deficiencies, particularly that of Fe.
Planting acid-tolerant crop species and genotypes within species is another
most cost-effective and environmentally sound approach to improve crop
production on acid soils. Some high soil acidity-tolerant crop species like
millet, rice, cassava, and cowpea could be produced with minimum input of
lime. In addition, some pasture grass and legume species have high tolerance
to soil acidity and these could be used in developing sustainable cropping
system for Oxisols. Some plantation crops also have high tolerance to soil
acidity and could be used effectively in acid ecosystem cropping systems,
along with annual crops. Low to medium acidity-tolerant crop species such as
soybean, sorghum, and peanut are suitable crops for low input farming
systems. High acidity-tolerant grasses, such as brachiaria and andropogon
and plantation crops such as rubber and oil palm, are suitable crops for
extremely acidic soils. In addition, soil acidity can be managed successfully
by adopting practices that maximize the biological activities in the soil, such as
nutrient mineralization and cycling, biological nitrogen fixation, and mycorrhizal symbiosis.
In areas where limestone quarries and transportation systems are well
developed, lime is almost always inexpensive and typically provides a very
high rate of return on investment. However, in some areas, transportation
costs have made lime very costly. In any case, lime should be viewed as an
investment in improving the production potentials of acid soils. Because of
the long-lasting residual effects of lime applications, the cost of liming may
be amortized over several crops. Common and scientific names of crop
species cited in the text are listed in Table 20.
ACKNOWLEDGMENT
We thank Dr. C. D. Foy for his critical review and valuable suggestions for improving this
manuscript.
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