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 naf@eco.unipv.it 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 soil-

plant 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 ~0-

10% 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 maize-

producing 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 non-

amended 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 resource-

poor 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; Blanco-

Canqui 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, well-

aerated, 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 VARIETY General Comments MAIZE SC403 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

weight(g)

Coleoptiles

length(cm)

Coleoptiles

weight(g)

Root

length(cm)

Root

weight(g)

Emergence

% 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

1.000

Coleoptile weight

0.620 1.000

Emergence %

0.122 0.599 1.000

Root length -0.270 -0.042 0.479 1.000 Root weight -0.455 -0.100 0.685 0.789 1.000 Seed weight 0.168 -0.230 -0.359 -0.815 -0.436 1.000 Coleoptile

length Coleoptile weight

Emergence %

Root length Root weight 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.

Figure 1: Figure shows the coleoptiles length and root length for the five treatments

0

5

10

15

20

25

trtnt 1 trtnt 2 trtnt 3 trnt 4 trtnt 5

coleoptile length

root length

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.

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.

Figure 3: Figure shows germination percentages for the five treatments at seven days after

planting

0

1

2

3

4

5

6

7

trnt 1 trnt 2 trnt 3 trnt 4 trnt 5

seed weight

coleoptile weight

Root weight

0

20

40

60

80

100

120

trtnt 1 trtnt 2 trtnt 3 trtnt 4 trtnt 5

germination %

germination %

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.

REFERENCES

Bloom AJ. 1997. Nitrogen as a limiting factor: crop acquisition of ammonium and nitrate. In: 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.

Fageria N K and Moreira A 2011 The role of mineral nutrition on root growth of crop plants. Advances in agronomy 110, 252-318.

Haefele, S.M., Knoblauch, C., Gummert, M., Konboon, Y., Koyama, S., 2009. Black carbon (biochar) in rice-based systems: characteristics and opportunities. In: Woods, W.I., Teixeira, W.G., Lehmann, J., Steiner, C., WinklerPrins, A.M.G.A., Rebellato, L. (Eds.), Amazonian Dark Earths: Wim Sombroek’s Vision. Springer, Berlin, pp. 445e463. Hass, A., J.M. Gonzalez, I.M. Lima, H.W. Godwin, J.J. Halvorson, and D.G. Boyer. 2012. Chicken manure biochar as liming and nutrient source for acid Appalachian soil. J. Environ. Qual. 41:1096–1106 (this issue). doi:10.2134/jeq2011.0124.

Irwin, M.P.S., 1981. The birds of Zimbabwe, Quest Pub.

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Major, J. (2010). Biochar for soil fertility enhancement and climate change mitigation. Montreal, Quebec.

Matsubara, Y.I., Harada, T., and Yakuwa, T., Effect of inoculation density of VAM fungal spores and addition of carbonized material to bed soil on growth of Welsh onion seedlings, J. Jpn. Soc. Hortic. Sci., 64, 549–554 (1995). Nyamapfene, K.W., 1991. The soils of Zimbabwe, Nehanda Publishers.

Shinogi Y., Yoshida H., Koizumi T., Yamaoka M., and Saito T., 2003. Basic characteristics of lowtemperature carbon products from waste sludge. Advances in Environmental Research 7: 661-665. Steiner, C.,Teixeira,W.G., Lehmann, J., Nehls,T., Macedo, J. L.V., Blum,W. E. H. and Zech,W.2007). ‘Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil’, Plant and Soil, vol 291, pp275–290 Taghizadeh-Toosi, A., Clough, T.J., Condron, L.M., Sherlock, R.R., Anderson, C.R., Tyron E.H., 1948. Effect of charcoal on certain physical, chemical and biological properties of forestsoils. Ecological. Monographs. 18: 82–115. Topoliantz, S., Ponge, J.F., 2005. Charcoal consumption and casting activity by Pontoscolex corethurus (Glossoscolecidae). Applied Soil Ecology 28, 217e224. Van Zwieten, L, Kimber, S, Downie, A, Morris, S, Petty, S, Rust, J & Chan, KY 2010a, ‘A glasshouse study on the interaction of low mineral ash biochar with nitrogen in a sandy soil’, Australian Journal of Soil Research 48(6–7): 569–76. Van Zwieten, L, Kimber, S, Morris, S, Chan, KY, Downie, A, Rust, J, Joseph, S & Cowie, A 2010b. ‘Effects of biochar from slow pyrolysis of papermill waste on agronomic performance and soilfertility’, Plant and Soil 327(1–2): 235–46. Vookova, B., Kormutak, A., 2001. Effect of sucrose concentration, charcoal, and indole-3-butyric acid on germination of Abies numidica somatic embryos. Biologia Plantarium 44, 181e184.

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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 VARIETY General Comments MAIZE SC403 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.]

AGR=

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.

RGR= X

Where, W is the mean total dry weight during the period (t2-t1).During the linear phase of the

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

)12(

)12(

tt

WW

−−

W

1)12(

)12(

tt

WW

−−

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.

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.

0

20

40

60

80

100

120

140

160

180

200

trtnt 1 trtnt 2 trtnt 3 trtnt 4 trtnt 5

plant height 1

plant height 2

plant height 3

plant height 4

rgr 1

rgr 2

rgr 3

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)

Figure 3: shows the shows relationship between plant height and biomass taken at week four

and eight after crop emergence

0

1

2

3

4

5

6

trtnt 1 trtnt 2 trtnt 3 trtnt 4 trtnt 5

Biomass 1

Biomass 2

Absolute growth rate

Relative growth rate

0

20

40

60

80

100

120

140

160

180

200

trtnt 1 trtnt 2 trtnt 3 trtnt 4 trtnt 5

biomass 1

biomass 2

plant height 1

plant height 4

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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