VOL. 2, Special Issue, ICESR 2012
ISSN 2225-7217
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AMELIORATING SOIL ACIDITY IN GHANA: A CONCISE REVIEW OF
APPROACHES
Franklin Obiri-Nyarko
Department of environmental protection and cartography,
Hydrogeotechnika Sp. zo.o, Poland
ABSTRACT
The paper concisely reviews the causes and effects of soil acidity and the approaches used to
ameliorate acid soils for sustained crop production in Ghana. Acid soils which are characterized as
toxic and impoverished, posing serious constraints to crop production were only visible in the
western part and lowland areas of the country, but have now become a nationwide threat. Both
natural and anthropogenic factors cause soil acidity. However, anthropogenic activities exacerbate
the rate of acidification. Application of lime, organic materials, the use of acid tolerant crops and
agroforestry are some of the management options adopted in curbing the menace associated with
soil acidity. A combination of lime and organic materials, however, are considered the most effective
management option considering their availability and long term effectiveness. There is also the need
to limit or curtail practices such as injudicious application of fertilizers that produce acidulating
effects, and practices that can greatly deteriorate the soil’s inherent fertility.
Keywords: soil acidity, crop production, amelioration, Ghana, tropical soils
INTRODUCTION
Agriculture is the main sector which absorbs the majority of the people in the country as
more than 60 per cent of country's population depends on agricultural activities in support of their
livelihoods Agriculture therefore plays a central role in promoting growth and poverty alleviation in
the Ghanaian economy.(Egyir and Beinpuo, 2009). It is the goal of every farmer in the country to
have high crop yields and to ensure their sustenance or betterment since they depend on such for
their livelihoods. Conversely, a decline in crop yields in most regions of the country has been
observed over the years. Significantly lower yields of 1.2 t/ha, 16 t/ha and 11 t/ha compared with
their potential yields of 5 t/ha, 28 t/ha and 37 t/ha for staple crops such maize, cassava and yams,
respectively, have been reported (MOFA, 2003; SRI, 2003). The gravity of this threat is so enormous
that it has culminated in food pressures and food insecurity, which has also necessitated the imports
of huge amounts of food into the country. In recent years, many discussions have centered on
identifying the reasons for the decline in crop yields of which soil acidification has been pinpointed
as one of the main factors. Soil acidification which used to be a problem only in the western parts
and lowland areas of the country is now a menace that threatens crop production nationwide.
Investigations by several researchers have indicated that soils in Ghana have increased in acidity over
the years, the rate of which is very alarming. A substantial proportion of agricultural soils
nationwide are currently ranging from very slightly to extremely acidic (Buri et al., 2005). Several
efforts have been made by both researchers and farmers to alleviate or control this problem. The
intent of this paper is to review some of the approaches adopted for acid soil amelioration in Ghana.
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CAUSES OF SOIL ACIDITY
Soils that are acid have pH values less than 7 on the pH scale (SSSA, 1997). Theoretically, soil
acidity is largely associated with the presence of hydrogen and aluminium ions in exchangeable
forms (Brady, 2001; Fageria and Baligar, 2003). Thus, the higher the concentrations of these ions in
soil solution, the higher the acidity. Most acid soils have been found to be low in fertility, have poor
physical, chemical, and biological properties. Crop production on such soils is seriously constrained,
particularly in areas where proper management measures have not been put in place (He at al., 2003).
Generally, soils have natural buffering capacity by which they are able to resist changes in soil pH
upon marginal increases in their acidity or alkalinity (Black, 1968). This natural buffering ability of
soils, however, varies from region to region as the parent materials and the unconsolidated soil strata
differ greatly in their physico-chemical properties. The buffering capacity of soils, regardless of the
location is, however, attenuated when soils are continuously exposed to processes that lead to soil
acidification. Soil acidity develops from a combination of natural and anthropogenic processes.
Naturally, soil acidity develops gradually over time as part of the soil development process and other
natural phenomena. In Ghana acidity caused via anthropogenic activities, however, by far exceeds
the natural causes of soil acidity. In some areas, anthropogenic activities have exacerbated the rate
of acidification caused through natural phenomena.
WEAT H ER IN G AN D L EACH IN G
Usually, the parent rocks or materials from which soils are formed are the main provenance
for both essential and non-essential plant nutrient elements. If the parent material is acidic, there
will be acidifying effect and alkaline effect on the hand will manifest if the parent material is basic.
During weathering both acidic and basic cations are released into the soil. The influx of these
nutrient elements to the soil is, however, annulled through leaching, where most of the basic cations
(Ca2+, Mg2+, Na+ and K+ ) that would counteract the acidity effects of the acidic cations (mainly H+
and Al3+ ) are removed from the soil, resulting in the preponderance of these acidic cations which
give rise to soil acidity. This process is very effective in areas where there is high temperature and
where precipitation exceeds evaporation and plant transpiration to induce weathering and leaching.
By reason of Ghana’s location on the globe, most of the soils, particularly those in the southwestern parts are naturally highly weathered and leached rendering them acidic and less fertile, hence
the predominance of Oxisols and Ultisols.
ORGAN IC M AT T ER DECOM POSIT ION
In the course of their lives, plants and animals take up nutrients in various forms. When
these plants and animals expire, the process of decomposition supervenes, whereby these organic
tissues are broken down into humus with a concomitant release of many sundry chemicals. As a
corollary of this eternal natural cycle, acids are either formed or consumed. Generally, organic
matter contains reactive substances such as carboxylic and phenolic groups which behave as weak
acids. The dissociation of these groups results in the release of H+ ions which are responsible for
acidity (Seatz and Peterson, 1964). Decaying organic matter also produces CO2 which reacts with
H2O to form weak carbonic acids. The conversion of organic N to mineral N through nitrification
can also increase soil acidity. Brady (2001), however, indicated that the contribution to acid soil
development by decaying organic matter is generally very small and it is only the accumulated effects
that might ever be measured.
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Acid rain
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Rainfall is characteristically acid and it is made so by oxides of sulphur and nitrogen fed into
the atmosphere from the internal combustion engines, the burning of coal and agricultural activities.
The acidity of the rain which can have a pH value between 4 and 4.5 (Brady, 2001) is imparted to the
soil through precipitation (Coy et al., 1990). The quantity of H2SO4 and HNO3 that is brought to the
earth in acid precipitation globally is enormous but the amount falling on a given hectare in a year
which can induce any significant changes in pH is somewhat low, particularly in the less
industrialized countries like Ghana. With time, however, the cumulative effects of acid precipitation
can influence both soils and plants that grow in them (Brady, 2001).
Crop production and removal
Obviously the main aim of any agricultural production system is to produce saleable
products. However, this often saddled with some problems such as soil acidifcation. The respiration
of plants and micro-organism in the soil is necessary for their survival. However, this results in large
quantities of carbonic acids with acidulating effects being produced. According to Black (1968),
however, this effect is relatively small because most of the carbonic acid decomposes and is lost to
the atmosphere as CO2. Also, the uptake of nutrients by plants results in partitioning of acidity into
the soil and alkalinity into the plant (Tang and Rengel, 2003). Crops absorb basic cations such as
Ca2+, Mg2+ and K+ and also NH4+ from the soil solution for their nutrition. Consequently, there is a
release of H+ from the plants in order for electrical balance to be established, particularly when
plants absorb nutrient in the form of NH4+. The release of these H+ ions has an acidulating effect in
the soil (Tisdale and Nelson, 1975). When these crops are subsequently harvested from the field, or
burnt and washed away via surface run-off, these basic cations which are responsible for
counteracting the acidity developed by other processes are lost and the net effect is increased acidity
(Chen and Barber, 1990). The amount of these nutrients removed by cropping, however, depends
on the type of crop grown, the part of crop harvested, and stage of growth at harvest. The leaves
and stem portions of the plant contain larger amounts of these basic nutrients than the grains.
Therefore, high-yielding forages such as Bermuda grass, hay and alfalfa have a larger effect on soil
acidity than grains when harvested.
APPLICAT ION OF ACID FOR M IN G FERT ILIZER S
Generally, as a result of high temperatures and other natural phenomena such as,
precipitation and incessant leaching of nutrients, there is deterioration of the soils’ inherent capacity
to support crop production. The continuous use of agricultural lands without appropriate
management measures to ensure their rejuvenation has also given rise to many infertility problems.
The levels of organic matter and most of the essential plant nutrients, particularly nitrogen and
available phosphorus are low in most Ghanaian soils. By reason of this intrinsic poverty of most of
the soils, most farmers depend on external sources of fertilization to replenish the soil of its fertility.
The reliance on chemical fertilizers far surpasses that of organic amendments for soil fertility
replenishment in Ghana. Chemical fertilizers mostly used in Ghana include ammonium sulphate
(AS), muriate of potash (MOP), urea, single and trisuperphosphate (SSP and TSP), etc. (FAO, 2004).
There is no denying the fact that significant successes in terms of crop yields have been recorded in
so many places via the use of such chemical fertilizers. Albeit these fertilizers are vital for high yields,
their use is saddled with many ramifications such as soil acidification.
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EFFECTS OF SOIL ACIDITY ON CROP PRODUCTION
Soil acidity has been shown to have detrimental effects on plant growth by affecting plant
nutrient availability and plant development. Two fundamental factors are associated with acid soil
infertility; nutrient deficiencies such as P, Ca and Mg, and the presence of phytotoxic substances
such as soluble Al and Mn. In the soil, plants absorb nutrients mainly in soluble forms. Under acidic
conditions some of the vital nutrients such as P, Ca and Mg are made unavailable in the soil solution
for plant uptake due to the abundance of elements such as Al and Mn. As mentioned in the
preceding chapters, soil acidity is usually associated with H+ and Al3+. Surprisingly, however, not so
much deleterious effects on plant growth as a result of increased activity of H+ ions under acidic
conditions have been documented compared to that of Al (Black, 1968; Rao et al, 1993). Soluble
aluminium in the soil causes most of the problems associated with acidic soils. The principal effects
on plant growth from soluble aluminium in the soil solution is increased acidity via Al hydrolysis and
reduced root proliferation and function, which is generally observed in the roots on field
the as
stunted, club shaped. This reduces the ability of plants to extract water and other nutrients in the
soil. Several studies have also shown that when Al is in abundance, P is fixed as aluminium
phosphate which is insoluble, hence making it unavailable for plant uptake (Fageria and Baligar,
2003). This is one of the main problems farmers in Ghana are faced with concerning acid soils.
With the exception of molybdenum, the availability of micro-nutrients generally increases as soil
acidity increases. Since micro-nutrients are needed by the plants in only minute quantities, plant
toxicity and other detrimental effects occur with excess amounts.
MANAGEMENT OF SOIL ACIDITY
The preceding sections have shown that soil acidity is an ongoing natural process which can
be augmented via anthropogenic activities. However, with appropriate management practices, soil
acidity and its deleterious effects can be mitigated or prevented. Studies have shown that a wide
array of possibilities exist for mitigating the effects of soil acidity. Some of the methods commonly
used in Ghana include liming, the use of acid tolerant crops (Sanchez, 1977), organic material
addition and agroforestry (Ofori, 1971; Lathwell, 1979; Dennis and Issaka, 1986; Anane-Sekye,
1997).
Liming
Several liming materials such as crushed limestone (CaCO3), dolomitic lime (CaMgCO3),
slaked lime (Ca(OH)2), quick lime (CaO) etc., can be used to reduce soil acidity. They can be used
either singly or in combined form. Studies have shown that apart from reducing the acidity of the
soil by counteracting the effects of excess H+ and Al3+ ions (Fageria and Baligar, 2005), liming also
has several other benefits including, its ability to reduce the toxicity effects of some micro elements
by lowering their concentrations while increasing the availability of plant nutrients such as Ca, P, Mo,
and Mg in the soil (Naidu et al., 1990) and reducing the solubility and leaching of heavy metals
(Lindsay, 1979; Sauvé et al., 2000). Crops absorb most of these nutrient elements particularly Ca, P,
and Mg in substantial amounts and therefore by increasing their amounts in soil crop yields can be
significantly improved. Application of lime is, however, affected by factors such as quality of the
liming material, soil texture, soil fertility, crop rotation, conservation tillage, crop species and the use
of organic manure (Fageria and Baligar, 2008). Several studies have been conducted to buttress the
beneficial effects of liming in Ghana. Lathwell (1979) conducted an experiment on improving the
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fertility of some acid and impoverished soils in Ghana by liming. The study revealed a concomitant
increase in pH and Ca+Mg contents and a decrease in Al concentration of the soil. This altogether
resulted in a mammoth increase in crop yield. In a similar experiment conducted elsewhere in the
country where 1.0 t/ha and 2 t/ha lime were applied, the authors recorded 72% and 48% increases
in yield, respectively, over no lime treatments (Buri et al., 2005). Other experiments conducted by
the same authors when they combined lime-phosphorus on an Oxisol and Ultisol with pH ranging
from 4.1-4.5 and 4.7-5.4, respectively, also showed a considerable increase in maize grain yield by
both lime and phosphorus. The apparent reason was the increase in pH and the availability of other
essential nutrient elements. Dennis and Issaka (1986) in their investigations indicated that by
applying lime at 0.5 t/ha to some forest Ultisols with pH range of 4.7 to 5.5, highly significant yields
over other treatments and a 73% increase in yield over the control was observed.
Application of organic materials
For simplicity, the use of organic materials herein represents all forms of organic materials
from both plants and animal origins. It has long been established that apart from improving the
fertility, structure and some biological properties of the soil, organic materials have the capacity to
reduce soil acidity and Al saturation. Though still enigmatic, a number of possible mechanisms have
been suggested by several workers in their quest to elucidate how this occurs. Plant materials
generally contain excess cations, and the balance between cations and anions is maintained by
synthesis of organic acid anions such as oxalate, citrate and malate (DeWit et al., 1963). During
microbial decomposition of plant materials, theses organic acid anions are decarboxylated (Yan et al.,
1996; Tang et al., 1999). Noble et al. (1996) therefore posited that the decarboxylation of organic
acid anions in the process of plant residue decomposition requires a proton for this reaction to be
complete. By consuming a proton, the hydroxyl ions increase and this results in an increase in
alkalinity. Thus the greater the content of cations in plant material, the greater will be this effect.
Plant materials such as legume residues (soybean, red clover, and acacia) were observed to have a
substantially higher Ca, Mg, and total basic cation contents than the nonlegumes (maize and
sorghum), and consequently, ash alkalinity values were also higher (Bessho and Bell, 1992; Pocknee
and Sumner, 1997; Wong et al., 1998). Another mechanism was adduced by Wong et al. (1998) who
indicated that functional groups associated with organic materials can also consume protons and in
the process, increase the alkalinity of the soil. To this extent, all the mechanisms presented are
related to organic acids.
A study was conducted by Safo et al (1997) to assess the effects of Palm bunch ash (PBA)
on growth of cowpea and the characteristics of a Ghanaian soil. According to the authors, the palm
bunch ash is very hygroscopic, extremely basic (pH 10-12) and contains 25-34% K, 3.6-5.5% Ca, 1.63.6% Mg, 0.5-1.7% P, and approximately 0.1% N. Their study revealed an incredible increase in pH
of about 2.5 units (4.7 to 7.2) and concluded that PBA applied at 4.0 mg/kg of soil may be as
effective as limestone in ameliorating acidity in poorly buffered soils. A more recent study conducted
by Arthur (2009) whose milestone was to investigate the changes in soil physico–chemical properties
following the application of crop residues on some acidic soils in Ghana found that when maize
stover was applied at 10t/ha for 3 years, the pH of the soil was significantly raised from 5.06 to 6.27.
It was indicated that the residue on the soil surface, apart from releasing alkali elements into the soil,
also protected it from raindrop impact that could lead to erosion and leaching of basic cations
(Schomberg and Steiner, 1999).
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Use of acid tolerant crops
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Although this approach is not able to reverse acidic soil conditions, the constraints of acid
soil to crop production can be alleviated by growing acid tolerant crops in such areas with limited
inputs such as lime (Clark, 1997). Quite a variety of crops have been found to thrive well in acid
soils because of their varying degrees of tolerance to acidity. Chillies, sweet and Irish potatoes are
among the crops that have shown tolerance to acidity and can somewhat do well in soils with pH
values well below 5.5. Most of the horticultural crops (onions, spinach, carrots, cabbages and
cauliflower), however, do not tolerate acidity and can only grow well in soils with pH values above
6.0. Cassava and rice are, however, some of the successful crops so far used in this regard (Rao et al.,
1993). Currently, most of the lowland areas occupying about one million hectares in Ghana have
been cultivated to rice with outstanding results (Buri et al., 2005).
Agroforestry
Though not clearly defined, the considerable potential for agroforestry as a land
management alternative for conserving soils as well as maintaining soil fertility and productivity in
the tropics is becoming obvious. It involves the deliberate integration of trees with crops on the
same land. Several positive effects have been documented from this interaction. Nutrients such as
nitrate, Ca, Mg, etc. leached from the root zones of crops to sub-horizons can be taken up by these
deep rooted species and return them to the surface via litter fall. Ridley et al. (1990) observed a
reduction in nitrate loss through leaching when deep rooted species such as perennial grass, multipurpose trees or shrubs instead of annuals were strategically located within crops in the field.
Agroforestry systems such multi-story systems can also reduce erosivity of rain drops and
leachability of nutrients. The ability of this system to reduce soil acidity, however, depends on the
tree species and the structure of the agroforestry system. Baggie et al. (2000) investigated the
potential of organic residues from nitrogen fixing trees such as Albizia zygia and Gliricidia sepium for
ameliorating acid infertile rice soil in Ghana. Their study revealed that after 4 weeks of incubation,
Albizia zygia and Gliricidia sepium had increased the pH of the soil from 4.4 to 5.1 and 5.3,
respectively due to the high content of basic cations in these tree species.
DISCUSSION
Both natural and anthropogenic activities cause soil acidity. Rapid population growth,
however, has increased anthropogenic activities thereby accelerating the rate of acidification and
aggravating its effects on crop production in Ghana. It is obvious that liming is the most commonly
used method in mitigating soil acidity and improving crop production on acid soils worldwide. Even
though several evidences regarding the beneficial effects of liming can be found in the literature,
inimical effects due to over application and some other limitations have also been documented. Over
application of lime has been shown to result in phosphorus adsorption and deficiencies of
micronutrients like Fe, Mn, Zn, Cu, and B. Another limitation of lime is its inability to reach the
subsoil when placed on the surface. Lime percolates extremely slowly to the subsoil and therefore it
has been recommended that it should be placed deeper in the soil in order to warrant any profitable
returns. However, this practice can be very expensive and may not be affordable by resource poor
farmers. According to Ismail et al, (1993), the low solubility of lime can be resolved by the using
gypsum (CaSO4). The effect of gypsum on subsoil pH is insignificant. However, it has high
solubility which makes it able to supply large amount of Ca ions deep into the soil. It is further
mentioned that the dissociated sulfates (SO42-) from the gypsum can combine with Al3+ ions to form
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aluminum sulfate (AlSO41+). The authors tentatively assumed that this compound can alleviate the
detrimental effects of Al3+ and can be less phytotoxic than Al3+ alone. This hypothesis was
corroborated by a study conducted to examine the effects of dolomitic limestone and gypsum on
corn growth on an Oxisol and Ultisol in Malaysia (Ismail et al., 1993). Lungu and co (1993) also have
reported that liming can be ineffective on some tropical soils because of the large amount of
leaching. Most tropical soils such as the Oxisols and the Ultisols have low cation exchange capacity
but high anion adsorption capacity due to the dominance of Al and Fe oxides and low organic
matter (Fontes and Weed, 1996) thereby leaving the positively charged macro nutrient elements at
the mercy of inclement weather. The effect of liming on the soil pH of tropical soils therefore
tends to be smaller and more temporary than in temperate soils. This may require the application of
large amounts of lime which can be worrying to the resource poor farmer (Shainberg et al., 1989).
In the early 80s, the then government of Ghana removed all subventions on agriculture. The
use of chemical inputs including lime in agriculture declined because the resource poor farmers were
unable to afford them, and most of them were also not readily available as all chemical substances
used the time were imported. The need for alternatives that were relatively cheap and locally
available became of paramount importance. Addition of organic materials was and is still one of the
cheapest alternatives, and investigations done by authors such as Hoyt and Turner, (1975), Ahmad
and Tan (1986), Bessho and Bell (1992), Wong and Swift (1995), Wong et al. (1995), and Wong et al.,
(1998) have all pointed to the fact that organic materials can be a suitable substitute for lime in acid
soil amelioration. Practically, the return of crop residues to the
field is an important agronomic
practice not only for nutrient recycling but also for minimising soil acidification through alkalinity
recycling (Yan et al., 1996). Some studies have even shown that some organic materials are more
effective than lime. Lungu et al (1993) conducted a study that compared the effects of lime and
farmyard manure (FYM) on the acidity and crop yields in tropical soils in Zambia. It was concluded
that, regardless of the rate of the lime applied, its effects on both soil acidity and crop yields could
not be substantiated. On the contrary significant effects of FYM was observed on both soil pH and
crop yield, while also reducing the levels of exchangeable Al in the top 20 cm of the soil. It is
therefore possible to infer that significant savings can be made by using these organic materials.
Nonetheless, the rapid rate of decomposition of organic matter due to high temperatures and
incessant rainfall can result in rapid wearing out of its effects. The relatively large amounts required
to neutralize acidity can also make its usage somewhat cumbersome and deterring. For example,
addition of 2 t ha-1 of lime led to an increase in pH of 0.2 - 0.6 (Buri et al., 2005) whereas an
application of 40-50 t ha-1 of organic matter resulted in increases of pH of 0.8 -1.9 (Haynes, 2001).
Antagonistic effects of some nutrients on others via application of organic materials have also been
reported by some authors. For instance the use of PBA in the study by Safo et al (1997) resulted in
high residual soil K and low residual soil Mg, leading to wide soil K/Mg ratios. The authors
therefore suggested that lower rates of PBA should be applied to ensure proper K and Mg nutrition
of cowpea and other plants on acid soils that are low in these plant nutrients. However, by lowering
its amount, its effectiveness may also be attenuated. It is also worth mentioning that, not all organic
materials can be used in this regard with positive results as they differ greatly in their composition
and ability to amend soils. Another reason that further affects its use is that some crop residues are
used as firewood and feed for animals.
There is, however, evidence intimating that when lime and organic materials are applied very
phenomenal results can be obtained. The reason stems from the fact that organic matter reduces Al
toxicity and its acidulating effects either by chelating or encapsulating the Al3+. In addition, it
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enhances plant growth through the improvement of physical properties and the fertility of the soil
and can also reduce leaching of basic cations. On the other hand, nutrients can be readily made
available for plant uptake by liming. A study done by Lungu et al., (1993) on an Ultisol to compare
the effectiveness of lime, wheat straw (organic matter), and their combination on the growth of
soybeans supported this assertion. The result of the work showed a significant effect for the
combined treatment by producing the tallest plants, the largest dry weights, and the greatest
reduction of Al toxicity and therefore. The case of Ghana shows that when a combination of lime
and organic materials is used significant results can also be obtained.
The use of acid tolerant crops is one of the alternatives for alleviating the effects of acid soil
on crop production. However, this has not been well embraced due to several reasons such as the
economic importance of these species, and ability to thrive in environmental conditions other than
acid soils. In addition, most of these acid-tolerant plant species do not encompass many of the
staple crops in Ghana. Continuous use of such lands will also result in soils gradually becoming
more acidic, and then the choice of crops will be very limited. Stringent efforts to further develop
more strains within the non-acid-tolerant plant species which can also grow in acidic soils and also
with the possibility of exuding some organic acids such as citrate, gluconate, malate or oxalate that
can chelate Al and reduce its toxicity effects in the rhizosphere (Bennet and Breen 1991; Conyers et
al. 2005) is necessary.
The massive campaign in the recent past about the use of agroforestry as a way of
rehabilitating degraded lands is in the right course. Notwithstanding the many advantages it has,
some disadvantages such as competition for water and nutrients during tree establishment phase and
long-term organic matter decline as suggested by some workers on long-term experiments in Africa
(Qureshi, 1991) are inevitable. Also, soils that are poorly buffered will increase in acidity in sub-layers
and may therefore not be beneficial for plant roots within such horizons. Further analysis of this
approach shows that it is not economical for farmers with farms that are small in size as land will be
too small to allow for the integration of tree species.
There are other measures that could be adopted to reduce soil acidity. For instance, in areas
where there is a risk of leaching by rainfall, there can be synchronization of nutrient supply and
plant uptake of nutrients. This may reduce leaching of nutrients and the effects of over application
of some acidulating chemical fertilizer. Selection of fertilisers to prevent or minimise acidic inputs
can also be useful. For example, it is possible to replace nitrogen fertilisers that are acidic
(ammonium related fertilizers) with nitrate fertilizers as N source because nitrate gives alkaline effect
since it is exchanged by plant roots with bicarbonate and hydroxyl ions. Sources of nitrates may,
however, be scarce and can be expensive, particularly for resource poor farmers, but whenever
available, it can be a good substitute.
CONCLUSION
As a natural process, soil acidification may only be reduced and not completely eliminated on
already-made-acid-soils. Preventive measures can, however, be adopted for the remaining which have
not yet been plagued by this menace by ensuring a balance in removal and input of soil nutrients. In
this review, however, it is inferred that a combination of organic materials and lime are effective
considering their merits and demerits and the case of Ghana. By this, problems such as high cost of
liming and the low supply and rapid putrefaction of organic materials can be reduced to the barest
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minimum. However, in areas where it is extremely expensive to apply lime and access to effective
organic ameliorants is a problem, the use of acid tolerant crops may be the best option. Its use is,
however, still in the infancy and therefore its potentials are yet to be fully tapped. Agroforestry has
unambiguous benefits but may not be able to eliminate soil acidity. Farmers are also encouraged to
limit or desist from using fertilizers that can have acidulating effects for correcting soils naturally low
in essential plant nutrients. In addition, there is the need to curtail or modify practices such as slash
and burn and continuous mining of soil nutrients without rejuvenating its fertility. Such practices
enhance rapid depletion of soil organic matter and hasten soil acidification. More sustainable and
soil rehabilitation practices such as recycling crop waste and crop rotations should be adopted. More
studies also need to be done in areas where there is potential for development, such as the
development of acid tolerant strains.
REFERENCES
Ahmad, F. and K.H. Tan. (1986). Effect of lime and organic matter on soybean seedlings grown on
an aluminum toxic soil. Soil Sci. Soc. Am. J. 50:656-661.
AnaneSakye, C. (1994). Organic matter and soil fertility management in the Northern Easter
Savannazone of Ghana. Proceedings of seminar on organic and sedentary Agriculture. Pp164181.
Arthur, A (2009). effect of decomposing crop residues on soil properties and crop productivity in
the semi−deciduous forest zone of Ghana. A Doctoral thesis submitted to the Department
of Crop and Soil Sciences, Faculty of Agriculture, College of Agriculture and Natural
Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Baggie, I., Zapata, F., Sanginga, N.; and Danso, S.K.A. (2000) Ameliorating acid infertile rice soil
with organic residue from nitrogen fixing trees. Nutrient Cycling in Agroecosystems 57: 183–
190, 2000.
Bennet RJ, Breen CM (1991) The aluminum signal: new dimensions to mechanisms of aluminum
tolerance. Plant and Soil 134, 153-166.
Bessho, T., and Bell, L. C. (1992). Soil solid and solution phase changes and mung bean response
during amelioration of aluminium toxicity with organic matter. Plant Soil 140:183-196
Black, C.A. (1968). Soil plant-relationships. John Willey and Sons, Inc. New York, London. Sydney.
792 pp
Brady, N.C. (2001). The Nature and Properties of Soils. Macmillan Publishing Company.
Buri, M.M., Wakatsuki, T., Issaka, R.N. (2005) Extent and Management of Low pH Soils in Ghana.
Soil Sci. Plant Nutr., 5 1 (5) . 755-759
Chen, J.H. and S.A. Barber (1990). Soil pH and phosphorus and potassium uptake by maize
evaluatedwith an uptake model .Soil Sci. Soc. Am. J. 54: 10320-1036.
Clark R B (1997) Effect of aluminium on growth and mineral elements of Al-tolerant and Alintolerant corn. Plant Soil 47, 653–662.
Conyers M, Helyar K, Moroni, J.S. (2005) The Carbon Cost of Protecting the Root Apex from Soil
Acidity: A Theoretical Framework. Plant and Soil 278, 195-204.
Coy L.D. ,Roy H.F. and W.T. Rodney (1990) Our soils and their management. Interstate Publishers ,
Inc.
Dennis, E.A. and Issaka, R.N. (1986): Management of low pH soils: Results of a preliminary study.
Paper presented at the 6thMaize and Cowpea workshop at Kum
DeWit, C. T., Dijkshoorn, W. and Noggle, J. C.. (1963). Ionic balance and growth in plants. Versl.
Landbouwkd. Onderz. Nr. 69.15.
151
VOL. 2, Special Issue, ICESR 2012
ISSN 2225-7217
ARPN Journal of Science and Technology
©2011-2012. All rights reserved.
http://www.ejournalofscience.org
Egyir, I. S., and Beinpuo, E.N. (2009). Strategic innovations in urban agriculture, food supply and
livelihood support systems performance in Accra, Ghana Department of Agricultural
Economics, And Agribusiness University of Ghana, Legon.
Fageria N.K. and Baligar, V.C. (2003) Fertility management of tropical acid soils for sustainable crop
production. In: Z. Rengel, Editor, Handbook of soil acidity, Marcel Dekker, New York, pp.
359–385.Fageria and Baligar, 2003a)
Fageria N.K. and Baligar, V.C. (2005). Enhancing nitrogen use efficiency in crop plants, Adv. Agron.
88 pp. 97–185.
Fageria, N.K. and Baligar, V.C. (2008). Ameliorating soil acidity of tropical Oxisols by liming for
sustainable crop production. Adv. Agron., 99:345-431.
Fontes, M. P. F. & Weed, S. B. 1996. Phosphate adsorption by clays from Brazilian Oxisols:
relationships with specific surface area and mineralogy. Geoderma 72:37- 51.
Food and Agriculture Organization FAO. (2004). Scaling soil nutrient balances. FAO Fertilizer &
Plant Nutrition Bulletin No. 15. Rome.
Haynes, R. J. (1984). Lime and phosphate in the soil-plant system. Adv. Agron. 37: 249–315.
He, Z., Yang, X., Baligar, V.C. and Calvert, D.V. (2003) Microbiological and biochemical indexing
systems for assessing quality of acid soils, Adv. Agron. 78, pp. 89–138.
Hoyt, P. B., and Turner, R. C. (1975). Effects of organic materials added to a very acid soil on pH,
aluminium, exchangeable NH4 and crop yield. Soil Sci. 119:227-237
Ismail, H. et al., (1993), "Alleviation of Soil Acidity in Ultisol and Oxisol for Corn Growth": Plant
and Soil, vol. 151, pp. 55-65.
Lathwell, D.J. (1979) Crop response to liming of Ultisols and Oxisols. New York College of
Agriculture and Life Sciences,Cornell International Agricultural Bulletin 35
Lindsay, W.L. (1979). Chemical Equilibria in Soils, John Wiley & Sons, New York.
Lungu, O.I., Temba, J., Chirwa, B. and Lungu, C. (1993), "Effects of Lime and Farmyard Manure on
Soil Acidity and Maize Growth on an Acid Alfisol from Zambia": Tropical Agriculture, vol. 70,
no. 4, pp. 309-313.
Ministry of Food and Agriculture (MOFA) (2003). Agriculture in Ghana: facts and figures.
Produced by the Statistics, Research and Information Directorate. Accra.
Naidu, R. Syers, J.K.. Tillman R.W and Kirkman, J.H. (1990). Effect of liming and added phosphate
on charge characteristics of acid soils, J. Soil Sci. 41, pp. 157–164.
Noble, A. D., I. Zenneck, and P. J. Randall. (1996). Leaf litter ash alkalinity and neutralization of soil
acidity. Plant Soil 179:293-302.
Ofori, C.S., ( 1971): Effect of lime application on maize yields on a forest Ochrosol. SRI Annual
Report 1970-71
Pocknee, S., and Sumner, M. E. (1997). Cation and nitrogen contents of organic matter determine
its liming potential. Soil Sci. Soc. Am. J. 61:86-92.
Qureshi, J. N. (1991). The cumulative effects of N–P fertilizers, manure and crop residues on maize
and bean yields and some soil chemical properties at Kabete. P. 160-167. In Recent advances
in KARI’S research programmes. Kenya Agricultural Res. Institute, Nairobi, Kenya.
Rao, I.M. et al., (1993). Selection and Breeding for Acid-Soil Tolerance in Crops": Bioscience, vol. 43,
pp. 454-465.
Ridley AM, Slattery WJ, Helyar KR and Cowling A (1990) Acidification under grazed annual and
perennial grass based pastures. Australian Journal of Experimental Agriculture 30: 539–544
152
VOL. 2, Special Issue, ICESR 2012
ISSN 2225-7217
ARPN Journal of Science and Technology
©2011-2012. All rights reserved.
http://www.ejournalofscience.org
Safo, E.Y., Ankomah, A.B, and Brandford-Arthur, J. (1997). Palm bunch ash effects on growth of
cowpea and the characteristics of a Ghanaian soil African Crop Science Journal, Vol. 5. No. 3,
pp. 303-308
Sanchez, P.A. (1977). Advances in the management of Oxisols and Ultisols in tropical South
America. p. 536–566. In Proc. Int. Sem. Soil Environ. Fertility Manage. Intensive Agric., Soc.
Sci. Soil Manure, Tokyo
Sauve, S. Martinez, C.E. McBridge M.and Hendershot, W. (2000). Adsorption of free lead (Pb2+) by
pedogenic oxides, ferrihydrite, and leaf compost, Soil Sci. Soc. Am. J. 64: 595–599.
Schomberg, H.H. and Steiner, J.L. (1999). Nutrient dynamics of crop residues decomposing on a
fallow no-till soil surface. Soil Science Society of America Journal 63: 607 − 613.
Seatz, L.F. and H.B. Peterson.(1964). Acid. Alkaline, Saline, and Sodic Soils. Pp 292. In F. EBear(ed.)
Chemistry of the soil. Reinhold Publishing Corporation, New York.
Shainberg, I., Sumner, M. E., Miller, W. P., Farina, M. P. W., Pavan, M. A. and Fey, M. V. (1989). Use
of gypsum on soils: A review. In Stewart, B. A. (ed.) Advances in Soil Science. Vol. 9. Pp. 111.
Soil Research Institute (SRI) ( 2003). The 2002 Annual Report. Accra
Soil Science Society of America, (Eds), (1997). In “Glossary of Soil Science Terms”. SSSA, Madison,
WI.
Tang C, and Z. Rengel (2003) Role of plant cation/anion uptake ratio in soil acidification. In
Handbook of Soil Acidity (Ed. Z. Rengel) , Marcel Dekker, New York. pp 5781
Tang, C., Sparling, G. P., McLay, C. D. A. and Raphael, C. (1999). Effect of short-term residue
decomposition on soil acidity. Aust. J. Soil Res. 37:561-573.
Tisdale J. and W.L. Nelson (1975). Soil Fertility and Fertilizers. Macmillan Publishing Co. Inc. pp 398.
Wong, M. T. F., Nortcliff, S. and Swift, R. S. (1998). Method for determining the acid ameliorating
capacity of plant residue compost, farmyard manure and peat applied to tropical soils.
Common Soil Sci. Plant Anal. 29:2927-2937.
Wong, M.T.F. and Swift, R.S. (1995). Amelioration of aluminum phytotoxicity with organic matter,
pp. 41-45. In: R.A. Date et al. (eds.), Plant-Soil Interactions at Low pH: Principles and
Management Kluwer Academic Publishers, Dordrecht, The Netherlands.
Wong, M.T.F., Akyeampong, E., Nortcliff, S., Rao, M.R., and Swift, R.S.. (1995). Initial responses of
maize and beans to decreased concentrations of monomeric inorganic aluminum with
application of manure or tree prunings to an Oxisol in Burundi. Plant Soil 171:275-282.
Wong, M.T.F., Gibbs, P., Nortcliff, S., and Swift, R.S. (1998). Measurement of the acid neutralizing
capacity of agroforestry tree prunings added to tropical soils. J. Agric. Sci. Camb. (submitted).
Yan, F., Shubert, S. and K. Mengel. (1996). Soil pH increase due to biological decarboxylation of
organic acids. Soil Biol. Biochem. 28:617-623.
153