NAF
International Working Paper Series
Year 2013
paper n. 13/03
Early crop growth and yield responses of
maize (Zea mays) to biochar applied on soil
WILBERT TIGERE MUTEZO
Department of Agriculture and natural resources
Faculty of Agriculture
Africa University
P.O Box 1320
The online version of this paper can be found at:
http://economia.unipv.it/naf/
Scientific Board
Maria Sassi (Editor) - University of Pavia
Johann Kirsten (Co-editor)- University of Pretoria
Gero Carletto - The World Bank
Piero Conforti - Food and Agriculture Organization of the United Nations
Marco Cavalcante - United Nations World Food Programme
Luc de Haese - Gent University
Stefano Farolfi - Cirad - Joint Research Unit G-Eau University of Pretoria
Ilaria Firmian -IFAD
Mohamed Babekir Elgali – University of Gezira
Firmino G. Mucavele - Universidade Eduardo Mondlane
Michele Nardella - International Cocoa Organization
Nick Vink - University of Stellenbosch
Alessandro Zanotta - Delegation of the European Commission to Zambia
Copyright @ Sassi Maria ed.
Pavia -IT
[email protected]
ISBN 978-88-96189-13-9
CHAPTER 1
INTRODUCTION
1.1.
Background of Study
Maize is the staple food in Zimbabwe which makes it a very important crop. However
average yields have been decreasing very much .As an example of differences in production
systems, the average white maize yield in Zimbabwe on large-scale commercial farms
averages over 4 tons per hectare, compared with around 1 ton per hectare in the small-scale
commercial and subsistence sectors. Much of that difference is the result of differences in
moisture regime and soil quality, but part would remain even if these latter factors were
controlled. Total maize output of over 2 million tones in the year 2000 was achieved. Since
then production fell rapidly to less than half of Zimbabwe’s requirements indicating a high
degree of food insecurity and an obvious lack of production self-sufficiency.
In some years the situation was worsened by rainfall deficits. In the year 2010 the estimate
for total national maize output was expected at around 400,000 tonnes. This output is about
20% of that required to meet national demand for this commodity (Cfuzim, 2011). The
reduction of maize yields is a result of reduced fertilizer application rates and nitrogen use
efficiency. There is reduced mineral availability as a result of reduced cation exchange
capacity in degraded soils. These soils have low pH levels and result in increases nutrient loss
especially nitrogen through leaching. The soils are generally becoming sandy with reduced
organic matter content.
Biochar application helps farmers in several ways: less fertilizer is needed because biochar
absorbs and slowly releases nutrients to plants; biochar improves soil moisture retention and
conserves water, securing the crops against drought; farmers spend less on seeds as
emergence percentages increases; biochar reduces the methane emissions from paddy fields
and farm yard manures; it increases the soil microbes and other soil-life density; it lessens the
hardening of soils; it supports better growth of roots and helps in reclaiming degraded soils.
Another advantage of biochar is that it can be used in all types of agricultural systems
(organic, chemical, permaculture, mixed farming, natural farming, etc) (Cushion et al., 2010).
Currently, very little biochar material is being used in agriculture in Australia and elsewhere.
Therefore, in the future development of agricultural markets for biochars, agronomic values
of these products in terms of crop response and soil health benefits need to be quantified.
Beneficial effects of biochar in terms of increased crop yield and improved soil quality have
been reported (e.g. Iswaran et al. 1980; Glaser et al. 2002a, 2002b). However, review of
previous research showed a huge range of biochar application rates (0 .5–135 t/ha of biochar)
as well as a huge range of plant responses (–29–324%) (Glaser et al. 2002a).
More importantly, in much of this research, properties of the biochar used in the investigation
were not reported.
Biochars can be produced from a range of organic materials and under different conditions
resulting in products of varying properties (Baldock and Smernik 2002; Nguyen et al. 2004;
Guerrero et al. 2005). Little research has been published elucidating the mechanisms
responsible for the reported benefits of the biochars on crop growth, production, and soil
quality. Such understanding is essential for development of agricultural markets for biochars
and for the future development of technology for the production of biochar products with
improved quality and value. Shinogi et al (2003) found, however, that biochar produced from
sewage sludge in Japan did not show harmful levels of heavy metals. Further research will be
required to investigate the possibility of using sewage sludge in different locations as its level
of contamination may be quite variable at different locations and at different times. Over the
course of time, it may be possible to develop the necessary infrastructure and social practices
to make collection of ‘clean’ sewage for biochar production a possibility.
Biochar can be described as a kind of charcoal made from the pyrolysis of a range of biomass
feedstocks, including crop, wood and yard wastes, and manures (Novak et al., 2009) .
“Biochar is the porous carbonaceous solid produced by thermo chemical conversion of
organic materials in an oxygen depleted atmosphere which has physiochemical properties
suitable for safe and long-term storage of carbon in the environment and, potentially soil
improvement.”(Steinbeiss et al., 2009). It is important to understand that biochar is not an
actual fertiliser although at times it can supply nutrients to plants, for example calcium,
potassium and magnesium. These are usually limiting in poor soils and the ash from biochar
could explain the strong effect of biochar on yields in these soils soon after application (Chan
et al., 2008).
1.2 Research Problem
Average attainable yields have declined very much as a result of soil fertility problems. There
is evidence of fertilizer use inefficiency especially nitrogen losses from leaching. Most
agricultural soils have been degraded due to continued use of unsustainable agricultural
tillage mechanisms. This has resulted in acidic soils reducing the crop yield. In rain fed crops
there is reduced crop emergence resulting in low population stands reducing the yields.
Global increases in carbon dioxide emissions from unsustainable agricultural practices have
resulted in global warming and changes in climate.
1.3 Justification
Average attainable yields can be increased using biochar as it improves fertilizer use
efficiency. There is a shift in crop production practices to mitigate the effects of changes in
climate in most countries and little has been done in Zimbabwe. The continued use of
unsustainable production practices will see the agricultural produce with no destination
export market and consequent increase in the global warming worldwide. Biochar application
in the soil helps address the changes in climate by carbon sequestration, mineral retention by
increasing cation exchange capacity hence effective fertilizer use and improved yields.
Biochar increases soil pH because of its buffering capacity improving the yields. It also helps
increasing crop emergence success rate which translates to higher crop stands and hence
increased yields. Biochar offers a wide range of answers to soil fertility improvement which
leads to improved yields and ultimately increased income and crop yields in crop production
for the marginal small scale farmer.
1.4 Objectives
1. Determine the effects of biochar on emergence of maize in the field
2. Determine the effects of biochar on the relative and absolute growth rates of maize in
the field.
3. Determine the effects of biochar on the above ground biomass of maize at early
flowering and physiological maturity in the field
4. Determine the effect of biochar on, CEC, soil pH and macro-nutrients levels at
planting and harvesting of maize
5. Determine the effect of biochar on the grain yield of maize at harvesting.
1.5 Hypothesis
1. Biochar increases the emergence of maize in the field because of its porous nature it helps
retain moisture for a longer period.
2. Biochar increases the relative and absolute growth rates of maize because it increases
mineral availability by increasing the cation exchange capacity.
3. Biochar increases the above ground biomass of maize at early flowering and physiological
maturity because it increases nitrogen availability by reducing leaching because of its
increased cation exchange capacity.
4. Biochar increases the soil pH and availability of macro-nutrients because of its pH
buffering ability
5. Biochar increases the grain yield of maize because it increases the fertilizer use efficiency.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Unlike fertilizers, biochar has an extremely long life in soils. Biochar is carbon-rich and gives
it the ability to stay long in the soil by not being susceptible to biological degradation.
Biochar also attracts microbes and beneficial fungi, holds on to nutrients that are put into the
soil that is biochar works better the second and third year than it does the first. One of the
major challenges in agriculture is making the nutrients in the soil available to the plant when
the plant can readily benefit from them. This might not be the case always because a lot of
things happen between the time the fertilizer is applied and the crop takes it up, fertilizers can
be leached out of the soil by excess rainfall, absorbed by weeds, or metabolized by microbial
activity in the soil. Biochar helps conserve plant nutrients by adsorbing them within its
matrix and making the nutrients available when the crop needs them. This happens because
of a property in biochar which is also found in certain clays, and soil organic matter known as
Cation Exchange Capacity (CEC). CEC is a measure of the capacity of biochar to retain ions,
such as ammonium and potassium cat ions, in an exchangeable form that is available to plants
for uptake. CEC not only helps in fertilizer use efficiency by the crop during the growing
season, but also improves the ability of the soil to adsorb and retain nutrients from other
sources available at other times. For example organic matter added at the end of the growing
season in form of crop residues often left in fields to decompose. When this organic matter
decomposes, biochar adsorbs some of the nutrients released on the soil active sites, leaving
those nutrients for the next growing season.
Biochar in soil holds moisture and save on irrigation costs. Biochar modifies the soil’s
performance by retaining moisture and making it available during periods of low
precipitation and hot, dry soil conditions. This is possible because biochars have very large
internal surface areas – typically over 100 square meters per gram. This internal surface area
adsorbs water molecules when water availability within the soil is high and releases it back
into the soil solution when water availability is depressed. Despite of its color being black,
biochar helps the soil stay moist even in full sunlight as opposed to often expected heating
from black surfaces. Biochar significantly impacts soil drainage. For example, clay soils
which are typically poorly aggregated are too tight and do not drain effectively. This results
in extended periods of inadequate soil aeration. Other soils, especially sandy soils may
exhibit excessive drainage. Overly drained soils can shorten the benefit of periodic wetting.
In both situations, the addition of biochar compensates for the native soil deficiency in the
following ways: Clayey and poorly aggregated soils become less compacted and provide
better aeration and sandy soils develop additional bulk moisture storage capacity. Biochar
also significantly contribute to mycorrhiza by promoting microbe populations. Mycorrhiza is
a fungus that has a symbiotic relationship with plant roots and contributes to a healthy soilplant nutrient exchange. Biochar increases the availability of mycorrhiza by: Detoxifying soil
water by adsorbing compounds that inhibit microbe growth, providing a protective habitat for
microbes and improving soil moisture management in which mycorrhiza thrives.
2.2 BIOCHAR: SIMPLICITY AND COMPLEXITY
Literally biochar is fairly simple. It is a black, fine grained, extremely porous, light weight
and stable form of carbon very similar to charcoal. It has certain physical and chemical
properties that make it a potentially powerful soil amendment. In this respect, biochar is
quite simple and really not all that unique. Contrarily, biochar represents a dynamic strategy
that could help solve many of the world’s most pressing problems. The process of creating
biochar could sequester billions of tons of carbon from the atmosphere every year
(somewhere on the order of 5-30% of global emissions) while simultaneously producing
clean renewable energy to replace fossil fuels.
Added on top of these two incredibly important functions, the benefits of preventing
groundwater pollution, enhancing fertilizer efficiency, decreasing greenhouse gas emissions
from soils, increasing famer’s profitability, providing low cost water filtration for developing
countries, providing an alternative to slash-and-burn agriculture, and reducing the amount of
material going to the landfill by approximately a third.
And then, of course, there is the
benefit that biochar which can be added to the soil to greatly enhance crop production and
soil fertility, particularly in degraded soils.
Biochar can be used to stop desertification and increase carbon in dry land soils. Pyrolysis
can be used in conjunction with decentralized heat and power plants. For small scale farmer
use purpose, biochar can be produced in high efficiency cook stoves. This makes it very
useful in developing countries to help cope with food security and as adaptive measure in
cases of drought. Thus, while biochar may be a rather simple substance, it also represents a
complex and multifaceted strategy which is gaining attention of farmers, energy experts, and
climate scientists around the world.
The idea of using charcoal to improve soils started from the study of ‘Terra Peta’ soils in the
Amazon Basin. Researchers uncovered large land areas of incredibly rich black soil on which
plants grew better, nutrient retention was stronger, and overall soil quality was superior to
that of neighboring soils. It was eventually hypothesized that it was native people who were
adding large amounts of biochar in addition to organic wastes in order to permanently
increase soil productivity in these habitation sites.
2.2.1 Biochar on CEC and pH on maize
Biochar reduces soil acidity which decreases liming needs, but in most cases it does not
actually add nutrients in any appreciable amount. Although biochars do not provide a
significant source of plant nutrients they can improve the efficiency of inorganic synthetic
fertilisers (van Zwieten et al. 2010) and nitrogen-fixing capabilities of Rhizobium spp. in
legume pasture and cropping systems (Rondon et al. 2007). van Zwieten et al. (2010) noted
increased crop biomass from the addition of a paper mill waste biochar combined with a
synthetic fertiliser, an effect that was not seen when the synthetic fertiliser was applied on its
own. They also found that this effect was more variable in an alkaline soil than a mildly
acidic soil and suggested that this may be due to the liming ability of the paper mill waste
biochar. The findings of van Zwieten et al. (2010) suggest that while biochars may not
provide a significant source of plant nutrients, they can improve the nutrient assimilation
capability of crops where they are applied, by positively influencing the soil environment.
Since most organic amendments contain plant nutrients in organic molecular structures which
must first be mineralised (Jeng et al. 2006; Mondini et al. 2008), several questions relating to
this process need to be answered to ensure the efficient use of these products as a plant
nutrient source. Is a slow mineralisation process efficient, potentially reducing the loss of
nutrients through leaching and volatilisation, providing plants with their requirements more
effectively over a longer time period? What temperature must soils reach before the process
of mineralisation enables the products to be of nutritional benefit to crops? What soil
moisture content is required before mineralisation via the microbial biomass will effectively
occur? The environmental and chemical processes influencing the mineralisation of organic
amendment in the soil need to be considered where the products are being applied for plant
nutritional purposes. Biochar made from manure and bones is the exception; it retains a
significant amount of nutrients from its source. Because biochar attracts and holds soil
nutrients, it potentially reduces fertilizer requirements. As a result, fertilization costs are
minimized and fertilizer (organic or chemical) is retained in the soil for longer. In most
agricultural situations worldwide, soil pH (a measure of acidity) is low (a pH below 7 means
more acidic soil) and needs to be increased. Biochar retains nutrients in soil directly through
the negative charge that develops on its surfaces, and this negative charge can buffer acidity
in the soil, as what happens with organic matter in general. CEC is one of many factors
involved in soil fertility. “Cations” are positively charged ions, in this case we refer
specifically to plant nutrients such as calcium (Ca2+), potassium (K+), magnesium (Mg2+) and
others. These simple forms are those in which plants take the nutrients up through their roots.
Organic matter and some clays adsorb these positively charged nutrients because they have
negatively charged sites on their surfaces, and opposite charges attract each other. The soil
can then “exchange” these nutrients with plant roots. If a soil has a low cation exchange
capacity, it is not able to retain such nutrients well, and the nutrients are often washed out
with water. Most biochar trials have been done on acidic soils, where biochars with a high pH
(e.g. 6 – 10) were used. One study that compared the effect of adding biochar to an acidic and
an alkaline soil found greater benefits on crop growth in the acidic soil, while benefits on the
alkaline soil were minor. In another study, adding biochar to soil caused increases in pH
which had a detrimental effect on yields, because of micronutrient deficiencies which occur
at high pH (>6). Care must be taken when adding any material with a liming capacity to
alkaline soils; however, it is possible to produce biochar that has little or no liming capacity
that is suitable for alkaline soils.
2.2.2 Biochar for soil remediation and land reclamation
Land reclamation generally relates to the improvement of soils degraded by human activities,
for example construction and unsustainable forms of agriculture. Soil remediation refers to
the process of removing, neutralizing or reducing the toxicity of certain compounds, often left
by human activities such as mining and industry. Each degraded and/or contaminated site is
potentially unique in its characteristics such as the presence of any specific contaminants,
land form topography, climate, watershed dynamics, proximity to vulnerable populations etc.
For this reason, whether biochar can be a tool to help with reclamation and remediation will
be situation-specific. Biochar can potentially facilitate the revegetation of degraded soils
through several mechanisms, and sorb a variety of compounds in soil. These multiple
potential benefits, combined with the fact that biochar can potentially be a relatively low-cost
and environmentally friendly tool for soil reclamation, provides incentive for more research.
Data presented here does not include the effects of activated carbon (AC) on soil properties,
although this has been widely studied. Biochar is the precursor to making activated carbon,
which typically requires an additional step for activation, for example exposure to a chemical
solution or gases. Depending on how they are made, some biochars may approach the
sorption properties of AC.
2.2.3 Biochar as a tool for revegetation
The potential for biochar to improve crop yields is receiving much attention. Often, the goal
is to facilitate the establishment of spontaneous vegetation on degraded soils which are acidic
and have low organic matter contents. Soil may become degraded due to human activities
such as mining and industrial activities as well as the use of certain pesticides in agriculture.
Some biochar materials have a high pH and can act as liming agents, to increase soil pH (e.g.
Chan et al., 2007; Novak et al., 2009; Major et al., 2010). In cases where organic matter and
clay levels in soil are low and soil is coarse textured, moisture retention may help the
establishment of vegetation. Biochar can help with this. Nutrient leaching can also be reduced
by biochar application to soil (Lehmann et al., 2003; Major et al., 2009; Novak et al., 2009;
Singh et al., 2010).
2.2.4 Biochar and the sorption of heavy metals
Biochar has been found to sorb a variety of heavy metals, including lead (Pb), arsenic (As)
and cadmium (Cd). For example a dairy manure biochar made at 350°C sorbed several times
more Pb than AC (Cao et al., 2009). In this case, sorption by biochar was attributed mostly
(85%) to the Pb reacting with ash present in the biochar, and also to direct surface sorption
(15%) on biochar surfaces. The authors of this study conclude that the ash in the manure
biochar was predominantly responsible for reducing Pb concentrations in water, as is also
evident by the fact that AC (very low ash) sorbed much smaller amounts of Pb than did
manure biochar.
Mohan et al. (2007) also worked on the removal of heavy metals in an aqueous solution by
biochars made from pine and oak wood and bark, at 400-450°C. Due to its greater surface
area and pore volume, oak bark biochar outperformed all others and removed similar amounts
of Pb and Cd from solution as did a commercial AC material (~100% for Pb and ~50% for
Cd). Oak bark biochar also removed ~70% of the As in solution. Other biochars, at pH values
in the range of those of most agricultural soils (5-7) removed ~5-25% Pb, ~0-10% Cd and ~010% As from solution. These authors concluded that metal adsorption by biochars occurred
by ion exchange mechanisms.
Biochar applied at 1% on a weight basis was found to reduce amounts of leachable metals in
contaminated soils containing phenanthrene, resulting in better decomposition of
phenanthrene and better plant growth. In this experiment, soil treatment with iron filings also
reduced metal mobility and improved phenanthrene degradation, but did not allow the
restoration of plant cover (Sneath et al., 2009). Because biochar has been shown to have
several different properties that enhance plant growth (Laird, 2008), this suggests that
applying biochar to contaminated soils will provide other benefits, beyond heavy metal
sorption and enhanced decomposition of organic contaminants (e.g. phenanthrene). In
another study, soil amended with 0.1 and 0.5 % (w/w) pine biochar sorbed more
phenanthrene than non-amended soil, although the authors found that the amount of this
contaminant sorbed by biochar varies with the properties of the biochar, soil characteristics
and contact time between biochar and soil (Zhang et al., 2010).
Uchimiya et al. (2010a) found that adding broiler litter biochar to soil enhanced the
immobilization of a mixture of Pb, Cd and nickel, and this was attributed to the rise in pH
brought about by the biochar. In a different study (Uchimiya et al., 2010b) tested the effect of
“natural” (non-biochar) organic matter and the biochar’s unstable carbon fraction, on heavy
metal immobilization by biochar. They found that these materials improve Cd immobilization
by biochar, had no clear effect on immobilization of Ni, and actually lead to greater mobility
of Cu in biochar-amended soil with very high pH (>9). Both high-ash and low-ash biochars
had the ability to reduce the mobility of Cd, Cu and Ni in this soil, and treating the biochars
with phosphoric acid to increase their negative surface charges improved the biochars’
immobilization capacity. Over a 60 day pot study using contaminated field soil and charcoal
made for cooking, Beesley et al. (2010) found that biochar was much more efficient than
compost (on a volume basis) in reducing the bioavailability of Cd and Zn, mostly due to the
fact that biochar raised the soil’s pH more than compost did. The availability of metals such
as these in soil decreases as pH rises.
2.2.5 Biochar and the sorption of pesticides and other organic molecules
Organic contaminants include many agricultural pesticides and industrial contaminants.
Biochar and the ash contained in biochar have a high affinity for sorbing different organic
compounds. Charred organic matter (i.e. biochar, soot, activated carbon) generally sorbs 10
to 1000 times more organic compounds than does un-charred organic matter (Smernik, 2009).
Indeed, the sorption of many organic molecules in soils and sediments, including polycyclic
aromatic hydrocarbons (PAH), has been attributed to the presence of biochar or similar
materials in these soils (e.g. materials resulting from vegetation fires or from fossil fuel
combustion). Sorption of organic molecules on biochar may be less reversible than sorption
on other forms of organic matter, i.e. the probability is lower that a sorbed molecule will later
detach itself. The sorption of organic molecules on biochar likely occurs by adsorption
directly onto biochar surfaces, thus the greater the surface area and porosity of a biochar, the
greater its potential for sorption of contaminants. While biochar is recalcitrant in soil, many
other compounds in soil can also sorb to biochar and saturate or “block” its surfaces. Thus,
more research is needed to determine the longevity of the effects of biochar on the sorption of
organic molecules (Smernik, 2009).
Although sorption dynamics are affected by pH and other factors in soil, many studies have
found that adding biochar to soil improved the sorption of pesticides. Cao et al. (2009) found
that biochar made from dairy manure sorbed more atrazine (herbicide) in an aqueous solution
than un-charred manure. Similar results were obtained by Zheng et al. (2010) for atrazine and
simazine, another herbicide. A study where diuron (herbicide) sorption was compared in
biochar amended vs. non-amended soils found that amended soil sorbed more diuron (Yu et
al., 2006). Similarly, Spokas et al. (2009) found that soil to which mixed wood chip biochar
was added sorbed more atrazine and acetochlor (herbicides) than unamended soil, but organic
matter applied to soil at the same rate as biochar would sorb more of these herbicides than the
fast-pyrolysis biochar they tested. In contrast, Wang et al. (2010) found that wood biochar
sorbed more terbutylazine (herbicide) than biosolids (digested or raw), and the herbicide was
also more strongly sorbed by wood-based biochar than by biosolids, in soil.
Yu et al. (2009) studied the microbial degradation of insecticides chlorpyrifos and carbofuran
in soil amended with wood-based biochar, and found that their degradation decreased with
increasing amounts of biochar applied, while the uptake of the insecticides by onion plants
also decreased with greater biochar application rates. This indicates that while the
insecticides remained in soil longer, their bioavailability to plants was reduced. Similarly,
Yang et al. (2010) worked with soil-applied insecticides chlorpyrifos and fipronil and found
that cotton straw chip biochar applied at 0.1 to 1% (w/w) reduced the losses of insecticides
from the soil, while the uptake by Chinese chive plants was also reduced. The authors suggest
biochar could be used to sequester these insecticides in a location while reducing their uptake
by plants.
Yu et al. (2010) found that eucalyptus wood biochars made at 450 and 850°C were both in
the range of 100 times more efficient at sorbing the fungicide pyrimethanil than was an
Australian soil. The biochar made at the higher temperature sorbed more fungicide and
released less of it after washing. Several studies assessed the effect of biochar-containing ash
on the sorption of pesticides. Yang et al. (2006) found that wheat straw ash containing 13% C
added to soil at 1% resulted in 7-80 times more diuron sorption than in un-amended soils, and
the amount of diuron remaining after 10 weeks was slightly greater in amended vs.
unamended soil. Thus, the bioavailability of diuron was decreased with ash/biochar as
demonstrated by a greater survival rate and biomass of barnyard grass. Yang et al. (2003)
also showed that wheat straw ash was 600-10000 times more effective at sorbing diuron than
unamended soil, up to 12 months after application. This has important implications for weed
management, where reduced herbicide activity is undesirable. Similar results were obtained
for benzonitrile (solvent) sorption by ash/biochar in soil (Zhang et al., 2006) and for MCPA
(herbicide), where ash/biochar amended soil was 90-1490 times more effective at sorbing
MCPA than unamended sandy soils (Hiller et al., 2007).
Polycyclic aromatic hydrocarbons (PAH) are potent contaminants which are produced by fuel
burning. Total PAH contents and PAH bioavailability in a contaminated field soil over 60
days was found to be reduced more by biochar than by compost (compared on a volume
basis), although not all treatment comparisons were statistically significant (Beesley et al.,
2010)
2.3 CONSTRAINTS TO MAIZE PRODUCTION
Average maize yields per unit of land have fallen in Africa partly because maize cropping has
expanded into drought-prone, semiarid areas (Gilbert et al. 19930, but a much greater
negative influence on mize yied has been the loss of soil fertility, especially in wetter areas
where yield potential is higher. The old and already highly leached soils in Africa’s humid
and sub-humid zones have inherently low nutrient levels. Sandy and sandy loam derived from
granite, with organic matter of less than 0.5% and very low cation exchange capacities, are
widespread in Zimbabwe, southern Zambia, and western and southern Mozambique.
Nitrogen deficiency is ubiquitous on these soils, while deficiencies of phosphorus (P),
sulphur (S), magnesium (Mg), and zinc (Zn) are common (Grant, 1981). On the sandy loam
and clay soils in Malawi, which are chronically deficient in macronutrients, micronutrients
such as S, Zn, and boron (B) are reported to be limiting at many sites (Wendt, Jones and
Itimu, 1994). The largest aggregate nutrient losses in Africa are seen in major maizeproducing countries with higher population densities and erosion problems. Smaling (19930
and Stoorvogel, Smaling, and Janssen (19930 estimated that annual net nutrient depletion
exceeded 30 kg nitrogen (N) and 20 kg potassium (K) per hectare of arable land in Ethopia,
Kenya, Malawi, Nigeria, Rwanda, and Zimbabwe. Buddenhagen (1992) estimated that,
discounting the effects of erosion, weathering of minerals and biological N fixation will
enable, at most, 1, 000 kg/ha of maize grain to be produced each year on a sustainable basis
in the tropics. Soil loss through erosion (and soils cultivated with annual crops in the upland
tropics are very prone to erosion) will reduce these yield levels considerably. Because
farmers are locked into low crop productivity per unit of land from a degrading natural
resource base, they will increasingly be forced to encroach on ecologically fragile
environments such as the Zambezi and LuangwaVAlleys, with their unique ecosystems and
remnant habitats for several endangered large mammals, and on the many hilly areas where
loss of protective vegetation will quickly lead to severe erosion.
2.4 LOW USE OF INORGANIC FERTILISER
In most parts of the world, chemical fertilisers play a major role in maintaining or increasing
soil fertility, but farmers in sub- Saharan Africa use very little chemical fertiliser. The FAO
(1988) has estimated that average fertiliser application in sub-Saharan Africa is 7 kg of
fertiliser nutrients per hectare of arable land plus permanent crops per year. Heisey and
Mwangi (1995) using similar criteria, gave an average of 10 kg of fertiliser nutrients per
hectare. Chemical fertiliser use is higher in some countries of southern Africa (notably
Zimbabwe, Zambia and Malawi) where the commercial farming sector is relatively wel
developed and fertiliser-responsive maize an important crop. Fertiliser application rates on
maize have been calculated at 70kg fertiliser nutrients per hectare of maize crop per year in
Zambia, 55 kg in Zimbabwe, and 26 in Malawi (Heisey and Mwangi, 1995). Nevertheless,
these levels are well below the crop and soil mantainance requirements and are likely to
remain so, because fertiliser is probably the most costly cash input used by smallholders in
southern Africa.
Aside from its costs, fertiliser is not used more widely because fertiliser recommendations are
frequently unattractive to smallholders. Recommendations often ignore soil and climatic
variation in the areas farmed by smallholders, are incompatible with smallholders’ resources,
or are simply inefficient. All of these shortcomings lead farmers who do apply fertiliser to
incur unnecessary expense. For example, in Zimbabwe farmers are instructed ti apply basal
fertiliser for maize in the planting hole at planting, but instead farmers almost always apply
fertiliser just after crop emergence, which is easier, less risky, and results in negligible loss of
yield under farm conditions (Shumba, 1989). This practice allows farmers, after a given rain,
to plant more area more quickly (important on a drying sandy soil), get better crop
emergence, and make more labour available for other operations. There is rarely a response to
K on the granite soils predominant in smallholder farming areas of Zimbabwe
(Mashiringwani, 1983; Hikwa and Mukurumbira, 1995), yet the recommended compound
fertiliser contains K as well as N and P. a better option might be to apply cheaper N alone,
just after planting, and cheaper forms of P at other times.
Even when fertiliser is used, the efficiency of its use on farmers’ fields (measured by the
grain yield response to the addition of chemical N and P fertilisers) is often poor, which
reduces the profitability of fertiliser use.
2.5 INSUFICIENT ATTENTION TO CROP NUTRITION STUDIES
In Africa, research agenda has been biased away from crop nutrition studies and towards the
gains that may be obtained through plant breeding. This basis is a legacy of the Green
revolution in Asia, which succeeded through the use of improved germplasm under very
different conditions- particularly Asia’s more fertile and uniform soils-than those prevailing
in Africa. Improved maize materials can make better use of available nutrients, but in the
absence of added nutrients, the gains from genetic improvement alone are small. Under low
N conditions, maize scavenges the N available in the soil very effectively, and little N is left
for the plant to take by flowering. For example, results from an extensive program of on-farm
demonstrations over four seasons in the major maize-growing areas of Malawi showed that
on relatively fertile soils and under good management, hybrids without fertiliser yielded just
1.4 t/ha compared with 0.9 t/ha for unimproved maize (Jones and Wendt, 1995).
Essentially two approaches can be used in managing soil fertility (Sanchez, 1995). The best
known approach, used in producing most of the world’s food, involves overcoming soil
constraints to meeting plant requirements through the application of purchased inputs. In fact,
much of the increase in crop yields in developing countries since the Green revolution,
especially in Latin America and Asia, can be attributed to the purchased inputs used by
greater numbers of farmers (Pinstrup-Andersen, 1994). The second approach relies more to
the biological processes to optimise nutrient recycling, minimise the use of external inputs,
and maximise the efficiency of input use. Our understanding of principles underlying this
second, more complex approach is not well developed, and knowledge gained in temperate
areas may be inappropriate for smallholder agriculture in the tropics.
2.6 Increasing inorganic fertiliser-use efficiency
There are several reasons to expect that biochar might decrease the possibility of nutrient
leaching in soils, and enhanced nutrient cycling has been cited in various field studies for
positive impacts on yield. However, very few studies have demonstrated the effect or
attempted to quantitatively describe the mechanism. In general, the mineral and organic
fractions of soil can both contribute to overall CEC, which affects the ability for soils to
buffer periodic flushes of ammonium that result from application of chemical fertilizers or
manures, or bursts of organic matter mineralization during favorable, seasonal conditions.
The adsorption of ammonium ions is a relatively loose association that does not necessarily
prevent plant acquisition, yet greatly mitigates the potential for leaching loss and the diffuse
pollution issues of drinking water quality and eutrophication of water bodies.
Since considerable fossil energy is required to fix nitrogen into fertilizer, a low ratio of
fertilizer nitrogen application to crop nitrogen uptake can impact the overall carbon balance
of agricultural activities. Higher fertilizer use efficiency should lead to a lower fertilizer
requirement per unit yield and usually lower nitrous oxide emission. Only certain mineral
constituents of soil contribute to CEC on account of abundance, and hence surface area, and
mineralogy, with certain types of clay being most important.
On a mass basis the exchange capacity of soil organic matter may be greater than for any clay
(and up to 50 times greater), but it is a relatively small proportion of soil mass in most
agricultural situations, particularly under tropical conditions. Given these factors, heavy
textured soils under climates that favour higher levels of organic matter show the highest
contributions of organic matter – about one-third – to total soil CEC (Stevenson, 1982).
Since mineralisation of organic matter is a major source of ammonium release in soil,
attempts to raise soil organic matter by increasing rates of input may not decrease – and can
potentially increase – leaching losses. In addition to the chemical stabilisation of nutrients,
the physical structure of soil determines its capacity to hold water, and hence soil nutrients in
solution.
There are several reasons to expect that biochar might modify leaching potential in soils.
Available evidence suggests that on a mass basis, the intrinsic CEC of biochar is consistently
higher than that of whole soil, clays or soil organic matter. An analogy may be drawn to the
extreme CEC of activated carbon, which is relevant to its function as a sorption medium for
decolourisation and decontamination. Since secondary thermal treatment of charcoal is one
means of carbon activation, it is not surprising that the process parameters impact the CEC of
primary biochar products with temperature increasing this property (Gaskin, 2007).
This is a function of both enhanced specific surface area and the abundance of carboxyl
carbon groups that they display. The indirect affect of biochar that may result from its
modification of soil pH has not yet been included in most studies by, for example, applying
lime to the control soil. Whilst determination of CEC and water release curves in
homogeneous materials such as biochar should be straightforward, it is more complex to
quantitatively determine the contribution of biochar once added to soil. Furthermore, the
observation that CEC of biochar may develop over time through both abiotic and biotic
modification of its surfaces (Cheng et al., 2006) implies that in order to develop a predictive,
quantitative understanding, methods to recover aged biochar from soil is required.
Information on the CEC of pyrolysis products is limited mainly by the availability of
materials produced from a sufficiently diverse range of feedstock under different production
conditions. Information on the CEC of char naturally present in soils is limited by isolation
methods, so available studies tend to rely on a comparison of whole soils amended and nonamended with biochar (Lehmann, 2003; Liang, 2006). The second mechanism for mitigation
of leaching relates to the physical retention of soil water, which may be enhanced by biochar
in coarse-textured soils and any indirect effect of biochar on the accumulation of soil organic
matter.
The inherent stability of biochar confers a distinction between the CEC benefits that are
possible compared to other soil organic matter; importantly there is no immediate constraint
to the level that can be attained by repeated addition, so in principal this capacity could be
incrementally enhanced. Provided that biochar is biologically stable, the benefit of higher
CEC may be obtained without the risk of contributing to seasonal flushes of nitrate. The
possible contributions of a modified soil water dynamics and CEC to the apparent effects of
biochar on nitrous oxide emission are evident. In addition to mitigating greenhouse gases
emissions, limiting gaseous nitrogen loss can be relevant to crop fertiliser requirement. A
beneficial impact of biochar on the plant-available phosphorus has been observed in soils
enriched with biochar, which in contrast to ammonium, is not a characteristic generally
associated with soil organic matter (Lehmann, 2007b; Steiner et al., 2007). In the context of
nutrient availability, the impact of biochar addition on pH may be important.
A central part of any strategy for expanding the number of smallholders who use inorganic
fertiliser will be to determine how to make the best use of limited amounts of fertiliser that a
typical is able to purchase. Increasing fertiliser-use efficiency will require a significant shift
in thinking for both researchers and policy makers in Africa. For instance, Zimbabwe has
more than a fifty-year history of agricultural research on inorganic fertilisers, but much of
this work was geared towards users who could afford relatively large quantities of fertiliser
(large commercial farms and growers of cash crops). Since independence in 1980, a great
deal of work has examined the appropriateness of types, amounts, timing, and placement of
inorganic fertilisers for food crops by smallholders, yet recommendations for inorganic
fertiliser have not given sufficient attention to the cash constraints and risk faced by resourcepoor farmers in marginal areas. Of the 325 of farmers in Zimbabwe who followed the
fertiliser recommendations for maize crop in the near-average season of 1990/91, 48% failed
to recover the value of the fertiliser (Page and Chonyera, 19994).
Additions of soil micronutrients can improve the yield response to macronutrients (N and P)
on deficient soils. Nutrients such as Zn, B, S and Mg can often be included relatively cheaply
in existing fertiliser blends, when targeted deficient soils, these nutrients can dramatically
improve fertiliser-use efficiency and crop profitability. There is evidence that the most
promising route to improving inorganic fertiliser efficiency in cropping systems is by adding
small amounts of high-quality organic matter to tropical soils (Ladd and Amato 1985; Snapp,
1995). High-quality organic manures (possessing a narrow C/N ratio and low percentage of
lignin) provide readily available N, energy (carbon), and nutrients to the soil ecosystem, and
they build soil fertility and structure over the long term. Their use will increase soil microbial
activity and nutrient cycling and reduce nutrient loss from leaching and denitrification (De
Ruiter et al. 1993; Snapp, 1995).
2.7 Soil organic matter and climate change
In order to understand the potential significance of carbon in soil in the form of biochar, its
characteristics and dynamics should be compared to those of the remaining soil organic
matter, which accounts for most of the carbon that exists in soil (the exception being
calcareous soils which contain stocks of inorganic carbon in carbonate minerals). Depending
on land-use and climate, most soils contain up to approximately 100 t/ha carbon as organic
matter. Peat soils, though, comprise mainly organic matter and contain much more carbon on
a per unit area basis. It is increasingly recognised, however, that a greater proportion of the
total carbon may comprise an accumulated store of the products from burning or fire
(Skjemstad et al., 2004a), and that this has implications for the response of the wider soil
carbon pool to climate change (Skjemstad et al., 1999; Lehmann et al., 2008).
Modelling indicates that about 90% of the organic matter present in soils turns over on
decadal to centennial timescales (Coleman et al., 1996; McGill, 1996). Most organic matter
in soil is derived from plant roots, plant debris and microbially degraded substances. The
presence of soil organic matter is important for a range of useful soil properties, which has
been comprehensively reviewed by Krull (2004). The process of microbial energy acquisition
(and concomitant carbon dioxide release) from substrate is accompanied by a release of
various nutrient elements, which may be conserved in the soil in microbial biomass or the
particulate residues of substrate decomposition.
A portion of certain nutrients may also be released in soluble form, and a fraction may be lost
from the soil through leaching or run-off; which is essential to crop nutrition. This is
particularly the case where external nutrient provision (from fertiliser or manure) is limited or
absent. Overall, a balance slowly develops between the rate of carbon addition and the
emission of carbon dioxide, which are specific to the land-use and environmental conditions.
The amount of organic matter maintained once this balance is reached, depends on its
average rate of turnover. To date there have been few means proposed that permit
manipulation of this rate, so that soil carbon can be permanently increased. Beyond simply
increasing the amount of external organic matter inputs (Smith et al., 2000), the main
strategies are to disturb the soil less by using less intensive tillage or zero tillage (Lal, 1997;
Smith et al., 1998), or by selecting particularly recalcitrant, lignin-rich amendments (Palm et
al., 2001).
Although conversion to no-till soil management has been widely promoted as an approach to
enhance soil organic matter as well as to control erosion and conserve water, the main effect
appears to be a vertical re-distribution of organic matter, and an increase toward the surface
more or less matched by a corresponding depletion at depth (Bhogal et al., 2007; BlancoCanqui et al., 2008). Nonetheless, the Chicago Climate Exchange includes a specification for
‘conservation tillage’ amongst its Carbon Financial Instruments for carbon sequestration and
thus a precedent for the active engagement of farming in the carbon market
18 (<http://www.chicagoclimatex.com/>).
Managing decomposition in soil by manipulating the quality of inputs has been explored
extensively in tropical environments where decay is rapid (Palm, 2001). But simply altering
the composition of soil inputs has only a relatively minor impact on the composition and
long-term fate of the small portion that is stabilized, with incorporation and repeated
decomposition inside the dominant, slow turnover pool. Thus the main emphasis in the
sequestration debate has been focused on increasing soil carbon by increasing organic matter
additions in the form of straw or other crop residues, and from external sources such as
manures and a range of organic wastes: sewage sludge, municipal compost, paper waste, and
so on. Although there is a large amount of such material available, the quantity is relatively
small compared with the total flux through soil, particularly the size of the global soil carbon
pool. When a soil is at equilibrium, only about 10% of the carbon added to soil is stabilized
for more than one year. During a transition, progress to new equilibrium is slow, with the
annual increase being small relative to the carbon invested. As equilibrium is approached the
annual rate of accumulation decreases, and once reached, the new level of input has to be
sustained simply to maintain it.
Furthermore, the capacity to store organic matter is ultimately limited (with the capacity
varying with soil type, water regime and climatic factors); thus the improvement in carbon
storage that is possible for each incremental increase in input (Stewart et al., 2007; Gulde et
al., 2008). As well as added carbon being rapidly re-emitted into the atmosphere, carbon is
lost in the formation of soil organic matter through digestion in the animal gut or oxidation in
conversion to compost. The level of carbon sequestration or offset that could be realised
through an alternative use of these materials, including fossil fuel substitution, must be
considered when assessing the efficacy of these strategies from the perspective of climate
mitigation alone (Schlesinger, 2000). For example, the carbon cost of producing N fertiliser is
relevant when proposing to increase soil carbon storage indirectly through enhanced plant
growth (Schlesinger, 2000).In the context of the interventions generically referred to as
‘management options’, important soil physical benefits may be gained by accumulating soil
organic matter (Janzen, 2006).
However, these must be balanced against the opportunity costs, the forgone benefits that
might arise from its breakdown and turnover, most importantly the release of crop nutrients
(Janzen, 2006). In general, however, any form of organic matter added to the soil degrades
resulting relatively quickly in carbon dioxide emission.
References
Chan, K. et al., 2008. Using poultry litter biochars as soil amendments. Soil Research, 46(5),
pp.437–444.
Cushion, E., Whiteman, A. & Dieterle, G., 2010. Bioenergy development: issues and impacts
for poverty and natural resource management, World Bank Publications.
Fruth, D.A. & Ponzi, J.A., 2010. Environmental Law: Adjusting Carbon Management
Policies to Encourage Renewable, Net-Negative Projects such as Biochar
Sequestration. Wm. Mitchell L. Rev., 36, pp.992–5249.
Irwin, M.P.S., 1981. The birds of Zimbabwe, Quest Pub.
Jeffery, M.I., 2011. CLIMATE CHANGE MITIGATION AND ADAPTATION POLICY
OPTIONS: REDUCING AUSTRALIA’S DEPENDENCE ON COAL, NATURAL
GAS, AND OTHER NONRENEWABLE ENERGY RESOURCES. Ind. Int’l &
Comp. L. Rev., 21, pp.447–509.
Lehmann, J., Gaunt, J. & Rondon, M., 2006. Bio-char Sequestration in Terrestrial
Ecosystems – A Review. Mitigation and Adaptation Strategies for Global Change,
11(2), pp.395–419.
Messenger, S.P., 2009. BIOCHAR: A Cost Benefit Analysis in the Scottish Whisky Industry,
VDM Verlag.
Novak, J.M. et al., 2009. Impact of biochar amendment on fertility of a southeastern Coastal
Plain soil. Soil Science, 174(2), p.105.
Nyamapfene, K.W., 1991. The soils of Zimbabwe, Nehanda Publishers.
Sparks, D.L., 2011. Advances in Agronomy, Academic Press.
Steinbeiss, S., Gleixner, G. & Antonietti, M., 2009. Effect of biochar amendment on soil
carbon balance and soil microbial activity. Soil Biology and Biochemistry, 41(6),
pp.1301–1310.
CHAPTER THREE
THE EFFECTS OF SEWAGE SLUDGE BIOCHAR ON THE SEEDLING GROWTH
AND EMERGENCE OF MAIZE IN THE RED SOILS FERSIALLITIC 5E OF
ZIMBABWE
3.1. INTRODUCTION
Maize can be grown on a wide variety of soils, but performs best on well-drained, wellaerated, deep warm loams and silt loams containing adequate organic matter and well
supplied with available nutrients. Although it grows on a wide range of soils, it does not yield
well on poor sandy soils, except with heavy application of fertilisers on heavy clay soils, deep
cultivation and ridging is necessary to improve drainage. Maize can be successfully grown on
soils with pH of 5.0-7.0 but a moderately acid environment of pH 6.0-7.0 is optimum.
Outside this range results in nutrient deficiency and mineral toxicity. High yields are obtained
from optimum plant population with appropriate soil fertility and adequate moisture. There is
need to examine ways to increase early seedling growth rate so as to improve on the
emergence success rate hence the yield increase. Biochar improves the physical conditions
around the crop-root zone and enhances crop production (Shinogi et al., 2003). For example,
5% charcoal application per weight doubles the hydraulic conductivity of loam soil. This
effect is dependent on soil type and can last for years. The amount of generated wastewater
sludge has increased dramatically due to urbanisation and industrialisation and is expected to
continue in the future.
Pyrolysis is one of the options for managing wastewater sludge where biochar produced
during pyrolysis can be applied as a soil amendment. Biochar from sewage sludge contain
phosphorus (P) and potassium (K) with citric type and these are essential nutrients for crops.
Land application of municipal sludge (biosolids) is a growing practice in agriculture (Bloom,
1997). Therefore, biochar from sludge can replace chemical fertiliser. However, nitrogen in
biochar a major nutrient for crops is not easy to be used by crops (Chen et al., 2007).
There is, however, considerable variation in plant and soil responses to biochar that cannot be
evaluated in a single study and may be lost in the overall message of a literature review.
Source of material and pyrolysis conditions (especially temperature) introduce significant
variation in the structure, nutrient content, pH, and phenolic content of the biochar products
(Novak et al., 2009a). Interactions with climate, soil type (texture, chemistry, hydrology)
(Tryon, 1948; van Zwieten et al., 2010a), and fertilization status (van Zwieten et al., 2010b;
Haefele et al., 2011) can also contribute to uncertainty in how biochar interacts with
organisms.
Sewage sludge biochar has been shown to increase plant productivity and yield though
several mechanisms. Soil physical conditions change with biochar; its dark colour alters
thermal dynamics and facilitates rapid germination, allowing more time for growth compared
with controls. Biochar can also improve soil water-holding capacity (Laird et al., 2010b),
facilitating seedling biomass gain (Kammann et al., 2011). Plant growth responses can also
be altered by biochar-induced changes in soil nutrient conditions, particularly the cycling of P
and K (Taghizadeh-Toosi et al., 2012). In the plant tissue K concentration and soil P and K
increased following biochar application.
These nutrients may be directly introduced to the soil through labile organic compounds
associated with biochar and become available as these compounds weather (Topoliantz &
Ponge, 2005; Yamato et al., 2006). This effect, however, depends on the production variables
of the biochar (Hass et al., 2012), and is short lived, as the nutrients are used by plants and/or
are leached from the soil (Steiner et al., 2007; Major et al., 2010). Biochar-type materials
have been reported to stimulate root growth for some time (Breazeale, 1906). The very
different properties of biochar in comparison to surrounding soil in most known cases
improved root growth. In fact, roots may even grow into biochar pores (Lehman et al., 2003).
Makoto et al. (2010) showed not only a significant increase in root biomass (47%) but also
root tip number (64%) increased within a layer of char from a forest fire with larch twigs,
birch twigs, and shoots of dwarf bamboo buried in a dystric Cambisol.
The number of storage roots of asparagus also increased with coconut biochar additions to
tropical soil (Matsubara et al., 2002). Germination and rooting of fir embryos (Abies
numidica) significantly increased from 10 to 20% without additions to 32-80% of embryos
when activated carbon was added to various growth media (Vookova and Kormutak, 2001).
Therefore, not only abundance, but also growth behaviour of roots may change in response to
the presence of biochar.
Soil compaction can result in yield reductions due to decrease in seedling germination, root
and plant growth, and nutrient uptake. The objective of this study was to look at the effects of
sewage sludge biochar on the emergence of maize.
3.2. MATERIALS AND METHODS
3.2.1. Site description
The experiment was conducted in the field at Africa University (AU) farm. The soil at AU is
a red Fersiallitic 5E soil under Zimbabwe soil classification system. The soils are strongly
sandy clay loamy soils (Nyamapfene, 1991). The average annual temperature is 19 °C,
surprisingly low for its moderate altitude (about the same as Harare which is 360 metres
higher.) This is due to its sheltered position against the mountain ridge of Cecil Kop which
encourages cool breezes from lower altitude to the east and south. The coldest month is July
(minimum 6 °C and maximum 20 °C) and the hottest month is January (minimum 16 °C and
maximum 26 °C), although as in much of Zimbabwe, October has the hottest days (28 °C).
The annual rainfall is 818 mm. Rain falls mostly in the months December to February
although heavy showers are possible before and after this period. The wettest month on
record was January 1926 which received 580 mm while January 1991 received only 24 mm
(Irwin, 1981).
Description of the crop varieties to be used.
CROP
MAIZE
VARIETY
SC403
General Comments
SC 403 is a very early white Maize Streak and Mottle
Viruses tolerant hybrid, with a relatively short, flinty ear
and excellent yield stability over a range of
environments with relatively slow dry down rate. It has
outstanding drought tolerance with very good
synchronization of silks. In numerous trials in
communal areas over several seasons, SC 403 has
performed very well under drought conditions. On
average, SC 403 has a higher yield potential over SC
401. SC 403 has hard, very dense grain and has
outstanding tolerance to both Diplodia and Furasium
cob rots. SC 403 is widely recommended for harsh
conditions where yields of less than 6t/ha are expected.
It is also recommended for irrigation schemes an early
Maize Streak Virus tolerant hybrid is required.
3.2.2. Experimental Design
Five treatments were used:
1. 15 tons/ha biochar.
2. 15 tons/ha biochar and 300 kg/ha Compound D (7:14:7, N: P2O5:K2O) fertilizer.
3. 15 tons/ha biochar and 150kg/ha Compound D fertilizer.
4. 300kg/ha compound D fertilizer.
5. No amendment (control)
The biochar was thoroughly mixed with the soil and/ or the fertiliser before planting. The
amounts of biochar incorporated were calculated on the 20mm ploughing depth. Two
kilograms of soil were used in each separate treatment. Each treatment was replicated three
times. For each of the three replicates of each treatment, twenty seeds (cultivar Sc 403) were
distributed evenly and buried 15mm into the soil or soil mixture and left for six days at room
temperature (250C). For all the three replicates, coleoptiles length and weight, root length and
weight and seed weight were assessed.
After washing, seedlings were separated into coleoptiles, root and seed and then dried at 650C
for 48 hours before dry weights were recorded. The biochar is from Mutare city council
sewage and water treatment department.
3.2.3. Data analysis
The effect of biochar or biochar and compound D mixture on the physiology of maize
seedling growth were analysed using GenStat Release 7.2 DE. Where significant effects were
detected in the ANOVA (P=0.05), means were compared using least significant difference.
For data where no significant effects were observed, means and standard errors are presented.
3.3. RESULTS
There were significant difference on germination and emergence among treatments (P<0.05)
Table 1: Table shows the mean seed weight, coleoptiles length, coleoptiles weight, and root
length and weight and emergence percentage at seven days after planting for the five
treatments.
Treatment
Seed
Coleoptiles
Coleoptiles
Root
Root
Emergence
weight(g)
length(cm)
weight(g)
length(cm)
weight(g)
% at 7 days
1
5.350a
9.767ac
0.4433a
21.40d
0.6433a
96.00a
2
6.473bc
10.800b
0.3883b
9.04a
0.1867b
70.00b
3
6.533c
9.867c
0.4000b
11.57b
0.6067a
99.33c
4
6.277bc
8.833d
0.1367c
11.17b
0.3900c
64.00d
5
6.140b
9.367ad
0.1400c
20.30c
0.7300d
82.00e
Columns with different letters shows means are significantly different (P<0.05)
Table 2: Table shows the correlation matrix for seed weight, coleoptiles length, Coleoptile
weight, and root length and weight and emergence percentage at seven days after planting for
the five treatments.
Coleoptile
length
Coleoptile
weight
Emergence
%
Root length
Root weight
Seed weight
1.000
0.620
1.000
0.122
0.599
1.000
-0.270
-0.455
0.168
Coleoptile
length
-0.042
-0.100
-0.230
0.479
0.685
-0.359
1.000
0.789
-0.815
1.000
-0.436
Coleoptile
weight
Emergence
%
Root length
Root weight
1.000
Seed
weight
Figure 1 below shows the differences in the coleptile length and root length for the five
treatments. This also confirms on the correlation of the two as given in the table 2 above of
the correlation matrix. The root length and coleoptile length are negatively correlated.
25
20
15
coleoptile length
root length
10
5
0
trtnt 1
trtnt 2
trtnt 3
trnt 4
trtnt 5
Figure 1: Figure shows the coleoptiles length and root length for the five treatments
Figure 2 below shows that seed weight is negatively correlated to coleoptile and root weight.
Table 2 above also show the same from the correlation matrix.
7
6
5
4
seed weight
coleoptile weight
3
Root weight
2
1
0
trnt 1
trnt 2
trnt 3
trnt 4
trnt 5
Figure 2: Figure shows the treatment difference for seed weight, coleoptiles weight and root
weight
Table 2 above shows that emergence percentage is positively correlated to all except for seed
weight alone. There is a correlation of nitrogen availability and crop emergence.
germination %
120
100
80
60
germination %
40
20
0
trtnt 1
trtnt 2
trtnt 3
trtnt 4
trtnt 5
Figure 3: Figure shows germination percentages for the five treatments at seven days after
planting
3.4. DISCUSION
Crop emergence was highest when biochar was applied with half the full fertiliser
recommendation as shown in figure 3 above. This was followed by biochar applied alone.
Surprisingly, the control emerged more than both the full fertiliser application without
biochar and full fertiliser application with biochar. Coleoptile lengths were highest in
treatments with biochar with full fertiliser application rate. This might have been caused by
high levels of nitrogen in the full fertiliser with biochar treatment. This will also confirm on
the ability of biochar to make nutrients readily available for crop uptake by increasing the
cation exchange capacity. High nitrogen levels around the seed will reduced seed germination
(Walter et al., 2003) as shown in figure 3 above. The seed act as the primary source of
nutrition before the crop is able to manufacture its own food by photosynthesis. Figure 2
shows that treatments with high seed weight showed a reduction in the coleptile and root
weight. This might suggest that there was interference between mineral availability in the soil
and hydrolysis of carbohydrates in the seed coat resulting in the negative correlation as
shown in table two above for root weight and coleptile length with seed weight.
The below-ground environment from which plants extract nutrients and water is highly
heterogeneous, both spatially and temporarily. For example, inorganic nitrogen
concentrations in the soil may range a 1000-fold over a distance of centimeters or over the
course of hours (Bloom, 1997b). Given such heterogeneity plants depend on various tropisms
(e.g. gravitropism, thigmotropism, hydrotropism and, perhaps even, chemotropism) to guide
root growth towards soil resources (Epstein and Bloom, 2005). The root length was smallest
in the treatment where full fertiliser without biochar applied. Walter et al. (2003) reported
that elongation of maize roots was faster in pure water than in nutrient solution containing
both NH4+ and N03-. In this research the control also showed highest levels of root growth
that all other treatments with either fertiliser and/or biochar applied.
High accumulations of free NH4+ in tissues are toxic because they dissipate pH gradients in
the mitochondria and plastids (Epstein and Bloom, 2005). This might explain why the roots
grew very slowly in the full fertiliser application with biochar treatment. The roots
accumulated high levels of free NH4+ in the meristems confirming the ability of biochar to
make nutrients available in the soil solution for plant uptake when it is used together with
inorganic fertilizers.
Similar work with wheat showed interesting below ground biomass difference between 0.05
and 0.5% biochar compared to the control. The investment in root growth and allocation of
resources to roots was a major factor to emphasize nutrient acquisition and consequently
higher plant growth at the fertilised 0.05 and 0.5% biochar application levels. The unfertilised
0.05% biochar application level seems to have enhanced the root resource availability of the
wheat. At the fertilised 2.5% biochar, the root investment was higher than the control.
However, this did not translate into higher growth of plant mass. The reason could be that
biochar affected the physical structural properties of the soil system (Downie et al., 2009) by
increasing the bulk density, inhibiting root growth, and thus , by extension reducing nutrient
uptake subsequently and plant growth (Fageria and Moreira, 2011). Proximity of seed to
fertiliser is important in assessing the risk of germination damage.
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Jackson LE, ed. Ecology in Agriculture. San Diego: Academic Press, 145–172.
Breazeale, J.F., 1906. Effect of certain solids upon the growth of seedlings in water
cultures. Botanical Gazette 41, 54e63.
Chan KY, Van Zwieten L, Meszaros I, Downie A, Joseph S (2007). Agronomic values of
greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45, 629–634.
doi:10.1071/SR07109.
Downie, A., A. Crosky and P. Munroe. 2009. Physical properties of biochar. In ‘Biochar for
environmental management : Science and technology.’ (Eds J Lehmann and S Joseph) pp.
13-32. Earthscan: London ; Sterling, VA, USA.
Craigie, R.A., 2011. Biochar incorporation into pasture soil suppresses in situ nitrous oxide
emissions from ruminant urine patches. Journal of Environmental Quality 40, 468e476.
Epstein E, Bloom AJ. 2005. Mineral Nutrition of Plants: Principles and Perspectives, 2nd
edn. Sunderland, MA: Sinauer Associates.
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CHAPTER 4
THE EFFECTS OF SEWAGE SLUDGE BIOCHAR ON ABSOLUTE GROWTH
RATE, RELATIVE GROWTH RATE AND PLANT HEIGHT OF MAIZE IN RED
FERSIALLITIC 5E SOILS IN ZIMBABWE.
4.1. INTRODUCTION
The term plant growth analysis refers to a useful set of quantitative methods that describe and
interpret the performance of whole plant system grown under natural, semi natural, or
controlled conditions . Plant growth analysis provides an explanatory, holistic, and integrative
approach to interpreting plant form and function. It uses primary data such as weights, areas,
volumes to investigate processes within and involving the whole plant or crops.
Organic manure such as crop residues, green manure, compost, farm yard manure, animal
wastes, municipal wastes, oil cake, and residues from food processing, can be used as an
alternative or supplement for inorganic fertiliser. Nutrients contained in organic manures are
released more slowly and are stored for longer time in the soil, thereby ensuring a long
residual effect (Sharma and Mittra, 1991), supporting better root development and higher
crop yield (Abou El-Magd, Mohammed and Fawzy, 2005), activates soil microbial biomass
thereby increasing soil fertility.
Several studies have shown that biochar amendment can enhance the growth and quality of
certain crop plants, although the mechanisms by which it does so are far from clear. As
observed by Jones (1976), yield of maize is significantly related to plant size: dry matter yield
in the early stages of maize growth would enhance grain yield. One of such cultural practices
is soil amendment by application of organic manure.
Sewage sludge biochar will help in the long-term improvement of soil fertility. During plant
vegetative growth, the flow of nitrogen from older to younger organs occurs at different
speeds, and the main source of nitrogen is always soil (Grezebisz, 2008). In the maturation
period, nitrogen taken up from the soil accounts for only a small portion of nitrogen
accumulated in generative organs (grains).
Most nitrogen comes from remobilisation of this element that was previously accumulated in
vegetative organs. Therefore, the more nitrogen is accumulated in the plant vegetative
organs/leaves the greater should be the yield. Numerous and regular applications of biochar
to soil are not necessary because biochar is not warranted as a fertiliser (Lehmann and
Joseph, 2009). In a pot trial carried out by Chan et al. (2007), a significant increase in dry
matter (DM) production of radish when N fertiliser was used together with biochar. The
results showed that in the presence of N fertiliser, there was a 95% to 266% variation in yield
for soils with no biochar additions, in comparison to those with the highest rate of 100t/ha.
Improved fertiliser-use efficiency, referring to crops giving rise to higher yield per unit of
fertiliser applied (Chan and Xu, 2009), was thus shown as a major positive attribute of the
application of biochar.
Major, (2010) conducted a study whereby a field trial demonstrated that a single dolomitic
lime and wood biochar application on an acidic, infertile Oxisol was sufficient to increase
crop yield and nutrition uptake of crops. A maize-soybean rotation was used for the study
which took place over several cropping seasons. In addition, inorganic fertilisers were equally
applied to both the biochar-amended and control soils. The maize yield gradually increased
with an increase in the biochar application rate in the ensuing years for the four years. These
yield increases were as a result of increases in pH and nutrient retention.
Furthermore, Lehmann et al. (2003) attributed the increase plant growth responses observed
to greater plant uptake of K, P, Ca, Zn and Cu with increasing biochar applications. In a study
conducted by Vaccari et al. (2011) positive effects on the growth, yield and grain quality of
durum wheat were observed when a large scale application of biochar was made. In general,
coarse-textured soils have a high risk of nutrient leaching that limits plant nutrient uptake,
fertiliser use efficiency and yield.
Growth analysis can be used to provide insight into any crop response to a fertiliser
application design and to the climate and its ultimate effect on yield. The objective of this
study was to determine the effect of biochar and fertiliser application rate on the relative
growth rate, absolute growth rate and plant height of maize grown in red loam soils. It also
looks at the response of maize to fertiliser use efficiency following biochar application.
4.2. MATERIALS AND METHODS
4.2.1. Site description
The experiment will be conducted in the field at Africa University (AU) farm. The soil at AU
is a red Fersiallitic 5E soil under Zimbabwe soil classification system. The soils are strongly
sandy clay loamy soils (Nyamapfene, 1991). The average annual temperature is 19 °C,
surprisingly low for its moderate altitude (about the same as Harare which is 360 metres
higher.) This is due to its sheltered position against the mountain ridge of Cecil Kop which
encourages cool breezes from lower altitude to the east and south. The coldest month is July
(minimum 6 °C and maximum 20 °C) and the hottest month is January (minimum 16 °C and
maximum 26 °C), although as in much of Zimbabwe, October has the hottest days (28 °C).
The annual rainfall is 818 mm. Rain falls mostly in the months December to February
although heavy showers are possible before and after this period. The wettest month on
record was January 1926 which received 580 mm while January 1991 received only 24 mm
(Irwin, 1981).
4.2.2. Description of the crop variety to be used.
CROP
MAIZE
VARIETY
SC403
General Comments
SC 403 is a very early white Maize Streak and Mottle
Viruses tolerant hybrid, with a relatively short, flinty ear
and excellent yield stability over a range of
environments with relatively slow dry down rate. It has
outstanding drought tolerance with very good
synchronization of silks. In numerous trials in
communal areas over several seasons, SC 403 has
performed very well under drought conditions. On
average, SC 403 has a higher yield potential over SC
401. SC 403 has hard, very dense grain and has
outstanding tolerance to both Diplodia and Furasium
cob rots. SC 403 is widely recommended for harsh
conditions where yields of less than 6t/ha are expected.
It is also recommended for irrigation schemes an early
Maize Streak Virus tolerant hybrid is required.
4.2.3. Experimental design: BIOCHAR IN MAIZE
The experiment will be a Randomized Complete Blocks Design (4 blocks) with five
treatments. The treatments will be:
1. 15 tons/ha biochar + 150Kg/ha AN (34.5%) top dressing
2. 15 tons/ha biochar and 300 kg/ha Compound D (7:14:7, N: P2O5:K2O) fertilizer +
150Kg/ha AN (34.5%) top dressing
3. 15 tons/ha biochar and 150kg/ha Compound D fertilizer+ 150Kg/ha AN (34.5%) top
dressing
4. 300kg/ha compound D fertilizer + 150Kg/ha AN (34.5%) top dressing
5. No amendment (control)
4.3Agronomic practices
4.3.1Planting
Maize will be planted in 90 cm inter-rows with intra-row spacing of 60 cm giving a plant
population of 37 000 plants. The plot will be 4*4 square meters in size. The seeds will be
buried manually into the soil for 4 cm and two seeds placed at each planting station.
4.3.2 Biochar and Fertilizer application
Biochar will be evenly spread on the soil surface. One and half kilograms (1.5 Kg/m2) of
biochar per every square meter will be applied. It will then be incorporated into the soil
before planting by hand hoeing. Biochar will be obtained from the pyrolysis of sewage sludge
from Mutare city council waste and water treatment department. Care should be taken as a lot
of dust is produced when applying. Fertilizers will be applied per plant station using fertiliser
cups as per the soil requirements and recommendations. Compound D will be applied as a
basal dressing at planting while AN (34.5%) will be applied as a top dressing at 4-6 weeks
after planting.
4.3.3 Weeding
Weeds will be controlled by hand-hoeing.
4.3.4. Watering
Maize plants will be watered with 2.5cm of water per week as supplementary irrigation in
absence of rainfall to reach their maximum potential. It will be of importance to put into
account the amount rain that falls in the area when determining how much to water.
4.4. DATA COLLECTION
4.4.1 Biomass
The above ground biomass will be determined at six weeks, ten weeks after planting and at
harvesting by cutting the whole crop just above the soil surface and oven dried for 72 hours at
600C. The dry weight will then be determined by weighing the dry crop parts. These values
will be used in calculating absolute and relative growth rates.
4.4.2. Absolute Growth Rate (AGR)
Increase in total dry weight per plant per unit time.
[Note: - this growth index is used specifically to quantify growth of single plants (e.g.:
in pot experiments) where the components of a crop (i.e. a plant population) spread
over a given land area is absent.]
(W 2 − W 1)
AGR=
(t 2 − t1)
Where, W1 and W2 are total dry weight per plant at times t1 and t2 respectively.
4.4.3. Relative Growth Rate (RGR)
Increase of total dry weight per unit time per unit of existing total dry weight.
(W 2 − W 1)
1
X
(t 2 − t1)
W
Where, W is the mean total dry weight during the period (t2-t1).During the linear phase of the
RGR=
growth curve W can be calculated as the simple arithmetic mean of W1 and W2.
4.4.4. Plant height
The plant heights will be measured on a weekly basis using measuring meter stick. Plants will
be sampled randomly and ten plants will be sampled each time. This will be computed to
determine plant early growth rate. This will be done from week six to week ten after crop
emergence.
4.5. DATA ANALYSIS
The effect of biochar or biochar and compound D mixture on the relative growth rate,
absolute growth rate and plant height were analysed using GenStat Release 7.2 DE.Where
significant effects were detected in the ANOVA (P=0.05), means were compared using least
significant difference. For data where no significant effects were observed, means and
standard errors are presented.
4.6. RESULTS
There were significant difference on absolute growth rate and relative growth rate among
treatments (P<0.05).
Table 1: Shows the absolute and relative growth rate means for the five treatments
Treatment
Absolute growth rate
Relative growth rate
1
1.258a
0.8758a
2
2.761b
0.9555b
3
1.679c
0.9049c
4
1.839c
0.9127c
5
1.061a
0.8814a
Figure 1 below shows the plant heights taken from week four to eight. The relative growth
rates were calculated from these plant heights to give the weekly growth rates. It can be seen
that the growth rates increased from the first week of recording to the eighth week showing
progressive growth in maize.
200
180
160
plant height 1
140
plant height 2
120
plant height 3
100
plant height 4
80
rgr 1
60
rgr 2
40
rgr 3
20
0
trtnt 1
trtnt 2
trtnt 3
trtnt 4
trtnt 5
Figure 1: Plant heights and relative growth rates from week four to eight. An increase in the
biomass did not translate to increased relative growth rate but had a positive correlation with
absolute growth rate.
6
5
4
Biomass 1
Biomass 2
3
Absolute growth rate
Relative growth rate
2
1
0
trtnt 1
trtnt 2
trtnt 3
trtnt 4
trtnt 5
Figure 2: Shows the relative and absolute growth rates calculated from the biomass taken at
week four and week eight after emergence (biomass 1 and 2 respectively)
200
180
160
140
120
biomass 1
100
biomass 2
plant height 1
80
plant height 4
60
40
20
0
trtnt 1
trtnt 2
trtnt 3
trtnt 4
trtnt 5
Figure 3: shows the shows relationship between plant height and biomass taken at week four
and eight after crop emergence
4.7. Discussion
Full fertiliser application with biochar showed the highest absolute growth rate and relative
growth rate. Reducing the fertiliser application to half the recommendation and applying it
with biochar showed no significant difference (P<0.05) with full fertiliser application rate.
Biochar alone showed no significant difference with the control (P<0.05) confirming earlier
studies that biochar is not a fertiliser. Biochar has the greatest ability to enhance plant growth
and nutrient content when combined with fertiliser application (Blackwell et al., 2009).
Neutral and negative plant growth responses have been observed with biochar-only
amendments, yet when combined with fertiliser additions, crop yields are increased to much
greater extent than with fertiliser additions in absence of biochar (Asai et al., 2009; Blackwell
et al., 2009). Decreased growth is regularly reported with biochar amendments when not
associated with fertiliser additions (Asai et al., 2009; Gaskin et al., 2010).
Numerous and regular applications of biochar to the soil are not essential because biochar is
not a fertiliser (Lehmann and Joseph, 2009). In a pot trail carried out by Chan et al., (2007), a
significant increase in the dry matter production of radish resulted when N fertiliser was used
together with biochar. The results showed that in the presence of N fertiliser, there was a 95
to 266% variation in yield for soils with no biochar additions, in comparison to those with the
highest rate of 100 t /ha. Improved fertiliser-use efficiency, referring to crops giving rise to
higher yield per unit fertiliser applied (Chan and Xu, 2009), was thus shown as a major
positive attribute of the application of biochar.
As the plant height increased from four to eight weeks after emergence, the relative growth
rates also increased as shown in figure 1. Figure 2 showed that an increase in the biomass
only affected the absolute growth rate but did not translate to an increase in the relative
growth rate. A huge increase in the plant height gave very small changes in the biomass of
the crop. Full fertiliser application with biochar showed increased plant heights. Since
biochar reduces exchangeable acidity, increased soil pH of acidic soils, and inherently
contains significant amounts of plant nutrients such as potassium, calcium and magnesium, it
is suggested that these are the main reasons for enhanced plant growth (Chan and Xu, 2009)
Increases in biomass will mean an increase in the photosynthetic capacity. This helps in
increasing the source of assimilate for the reproductive structures which might translate to an
increased grain yield. According to Grzebiesz (2008), most carbon accumulated in grain
comes from running photosynthesis of photosynthetically active organs. The grain demand
for assimilates is so high that generative and vegetative organs or particular generative
structures compete with each other. The older the acceptor, the greater the odds on its
accumulation of a respectively high amount of carbon, which obviously has its repercussions
for the amount of produced generative yield.
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