ABSTRACT
Promiscuous (naturally nodulating) IITA (International Institute of Tropical Agriculture)
soybean (Glycine max (L) Merrill) varieties and elite varieties of maize (Zea mays L.) were
evaluated in four experiments between 2007 and 2009, for their growth and yield responses to an
area without history of soybean cultivation, some soil fertility management options and for
soybean fertilizer replacement value (FRV) to companion and subsequent non-legume maize
crop. These experiments were conducted at Abakaliki in the derived Savanna of Southeastern
agro-ecological zone of Nigeria, located at latitude 060 19´ 407´´ N, longitude 080 07´ 831´´ E
and an altitude of about 447m above sea level, with a mean annual rainfall of about 1700mm to
2060mm spread between April and October. The maximum mean daily temperature is between
270 C – 310 C with abundant sunshine and a high humidity all through the year. The soil is
shallow with unconsolidated parent materials (shale residuum) within 1m of the soil surface,
described as Eutric leptosol.
The first experiment assessed twelve IITA promiscuous soybean varieties (TGx 1740-2F, TGx
1904-2F, TGx 1904-4F, TGx 1903-5F, TGx 1909-3F, TGx 1844-4E and the selected six
varieties used in Experiment II), for their growth and yield performances in the derived savanna
belt of Southeastern Nigeria. These varieties showed high adaptable potentials by exhibiting
significant good growth and high yield components. Varieties like TGx1740-2F, TGx1485-1D,
TGx1904-6F, TGx1908-8F, TGx1903-5F, TGx1844-18E, TGx1904-2F and TGx1903-7F
produced seed grain of up to 6.0-7.5 tons/ha, seed weight between 29.1-33.5 g/plant, nodule
number between 20.9-37.1 and a vigorous growth to a height of up to 30.8-69.3 cm with girth
size of 1.2-1.5cm. These qualities observed were good evidence that soybean can be successfully
cultivated in Abakalki climatic conditions and that with application of the management options
implicated in this study, soybean can be a veritable resource among the resource-constrained
smallholder farmers for food and for their soil fertility improvement without the costly external
fertilizer inputs.
In Experiment II, eight soil fertility management options (lime at 10 tons/ha, wood ash (WA) at
10 tons/ha, urea at 20 Kg/ha, poultry manure (PM) at 20 tons/ha, muriate of potash (MOP) at 30
Kg/ha, single super phosphate (SSP) at 40 Kg/ha, NPK (15:15:15) at 40 Kg/ha and a control)
were evaluated for their effects on the growth and yield of six selected soybean varieties
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(TGx1876-4E, TGx1903-7F, TGx1485-1D, TGx1844-4E, TGx1904-6F and TGx1908-8F) from
Experiment I. A soil test was carried out before planting (BP) and after harvesting (AH), which
indicated that the area was acidic with pH values between 5.50 (BP in 2008) and 5.85 (AH in
2009), but with high available phosphorus (24.57 mg/kg AH in 2009) while other elements were
low. Poultry manure was found highly significant (P<0.05) in improving the growth and yield of
the six soybean varieties, seedling emergence (71.1%), plant height (39.59 cm), the girth size
(1.27 cm), number of branches (3.13), number of nodule/plant (25.25), number of pods (106.2),
weight of pods/plant (39.78 g), number of seeds/plant (209.80) and weight of seeds/plant (23.68
g). Wood ash was next in improving the growth and yield parameters but not with the same
degree with PM. Lime was next to WA, followed by urea, NPK (15:15:15), MOP, SSP, and the
control in their effects. TGx1485-1D responded better in terms of number of nodules per plant
(12.70) and number of pods per plant (119.2) than others, but TGx 1903-7F had the highest
number of seeds per plant (160.5) and weight of pods (31.28 g/plant). TGx 1904-6F (medium
maturing) had the least number of nodules (9.39) but was second to the highest in terms of
number of seeds (145.4). No one variety responded better than others across all the parameters.
The fertilizer replacement value (FRV) of soybean residual manure (SRM) was evaluated in
Experiment III on the growth and yield of subsequent three maize varieties. SRM + NPK
(15:15:15) at 200 Kg/ha significantly (P<0.05) influenced the growth and yield parameters of
maize varieties than soybean residual manure alone, NPK (15:15:15) alone and the control.
Where SRM + NPK (15:15:15) were applied, it gave the highest shelling weight (18.75 g) per
plant and 1000 seed weight (196.73) but was third in influencing harvest index (HI) with 0.56 as
against 0.59 arising from NPK (15:15:15) and 0.57 from control. However, SRM alone
contributed almost one half (9.08 g) of the shelling weight arising from SRM + NPK (15:15:15),
but had the least HI (0.53). Also, SRM + NPK (15:15:15) had the highest undehusked cob
weight (29.42 g) and dehusked cob weight (23.38 g) per plant. Composite maize breed, Suwan
produced the highest shelling weight (14.59 g) and was second to Oba super II in HI (0.60) with
0.58. But the local (Ikom white) yielded the highest 1000 seed weight 209.38 g, followed by
Suwan (193.02 g) and Oba super II (171.10 g).
The fertilizer replacement value of twelve soybean varieties on the growth and yield of a
companion crop was evaluated in Experiment IV by intercropping soybean (30 x 15 cm) with
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maize (75 x 25 cm). The yield performance of the maize varieties showed that the HI of Oba
super II was lower (0.46) in 2008 than in 2009 (0.59), and was like that for Suwan, 0.46 (2008)
and 0.55 (2009) and 0.43 (2008) and 0.57 (2009) for Ikom white, indicating that by intercropping
soybean with maize, maize growth and yield could be sustained successfully without inorganic
fertilizer application and without the maize developing any deficiency symptoms.
TABLE OF CONTENTS
Title page ………………………………………………….. i
Certification………………………………………………………… ii
Dedication……………………………………………………………. iii
Acknowledgment……………………………………………………. iv
Table of contents…………………………………………………….. vi
List of Tables………………………………………………………….. vii
Abstract………………………………………………………………. ix
Introduction……………………………..……………………………. 1
Literature Review……………………….……………………………. 9
Materials and methods……………………………………………….. 30
Results…………………………………………………………………. 35
Discussion………………………………….…………………………… 82
Conclusion………………….…………………………………………. 97
Reference……………………………………………………………….. 98
Appendix…………………………………………………………………
CHAPTER ONE
NTRODUCTION
There is a growing concern all over the continent of Africa over the decline in the productive
capacity of the continent’s soil resources due mostly to declining soil fertility with cultivation.
Agricultural productivity is reported to have actually declined over the past 45 years in many
African countries which has been blamed on soil degradation as its major cause (Bluffstone and
Köhlin, 2011). Sanchez (1987) had earlier observed that soil fertility depletion is the
fundamental cause of low per capita food production among smallholder farmers in Africa who
remove huge amounts of nutrients from the soil without returning any at the rate of 22 kg N, 2.5
kg P and 15 kg K per hectare over the past 30 years in 37 African countries (Anon, 2003).
However, reports show that where farmers applied fertilizers at all, very little are used as low as
less than 20 kg/ha which is strikingly low compared with the 200 kg/ha common in European
agriculture (Tittonell et al., 2008). “African Green Revolution” in which fertilizer use is expected
to rise from 8 kg/ha to at least 50 kg/ha annually by 2015, was launched in Abuja, Nigeria to
indicate the need for increased fertilizer use in Africa, known as “Abuja declaration 2006”.
Almost all agricultural intensification to guarantee food security for all, hinges on heavy use of
fertilizers (ENDA, 1977), but the tropical soils do not respond well to some of the temperate
farming practices involving the use of fertilizers, herbicides and pesticides (Houngnandan et al.,
2000).
There is a strong nexus between soil fertility management and demographic growth rate
especially in Africa where food production is lagging behind demand for food. Rapid population
growth and urbanization consequently led to increased demand for land especially for cultivation
of food crops to avert hunger. The consequent severe pressure on soil productivity made most
soils lose their fertility quickly (Kang et al., 1984, Kang and Reynolds, 1986, Spore, 2009). The
more the population the more access to good agricultural land is restricted in regions where land
area per capita is continually decreasing, yet it is these regions where the demand for agricultural
products is continually rising (Spore, 1994) and consequently requiring land use intensification.
Soil study and fertility interpretations of the Southeastern Nigeria indicated the following
categorizations of soil fertility guide for fertilizer application needs.
Category Total N (%) Available P
(Bray-2, mg/kg)
Exchangeable K
(Cmol/kg)
% Organic
matter
Low <0.15 <15 <0.20 <2.0
Medium 0.15-0.20 15.0-25 0.20-0.40 2.0-3.0
Adequate >0.20 >25.0 >0.40 >3.0
Source: NRCRI, Umudike soil Laboratory
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Traditionally, the African smallholder farmers who produce most of the food for the developing
world have enough understanding of how to manage the soil fertility of their farm lands
sustainably. The changes in the natural environment were accommodated within the culture and
agriculture of their specific geographical areas, until the rapid changes in population growth
during the 20th century (LEISA, 2006). The traditional shifting cultivation acclaimed to be
ecologically stable and biologically efficient and suitable for the fragile tropical soils with
inherent resilience, was no longer feasible, as the fallow periods continued to decrease due to
increased pressure on land resulting in reduced crop yields (Glen and Tipper, 2001), demanding
a more technical farming system than ever, to catch up with population increase and changes in
farming environment in terms of food production (Anon, 2004). The principal factors of soil
quality are soil salination, pH, microorganism balance and prevention of soil contamination.
Agro-forestry closely approximates the traditional shifting cultivation but suffered low
acceptance by great many smallholder farmers (Giller, 2003) because the smallholder farmers
will better accept any technology that can both provide for soil fertility improvement and
immediate food and fibre security (Catacutan et al., 2001). The use of such research technologies
and concepts can improve soil fertility, but their application or acceptance is generally bolstered
when they fulfill indirect benefits. Misiko (2007), indicated that as labour force dwindles and
farm sizes shrink, the resource-deprived smallholder farmers would expect high economic
returns such as food, fibre, fodder and fertilizer to pay for labour and time expended on them,
beyond simply improving soil fertility.
Legume crops
Patrick et al. (1957), indicated that cover crops improved soil quality by increasing soil organic
matter levels over time which enhanced soil structure as well as the water and nutrient holding
capacity and buffering capacity of soils, increased soil carbon sequestration to offset the risk of
increased atmospheric carbon dioxide levels (Kuo et al., 1997, Sanju et al., 2002, Lal, 2003).
Soil erosion is prevented due to network of roots formed. There is increased soil porosity and
suitable habitat networks for soil macro fauna (Tomlin et al., 1995).
Intercropping
Intercropping is an age old traditional practice of growing two or more crops in proximity in the
same field during a growing season. It promotes ecological principles such as diversity, crop
interaction and other natural regulatory mechanisms (Amanor, 1994). It is a plan for
3
simultaneous crop production and building up of soil fertility, prevention of nitrogen leaching
risks, sometimes observed in sole crops such as grain legumes, due to changes in incorporated
residue and chemical quality involving nutrient turnover. Available growth resources, such as
light, water and nutrients are more completely absorbed and converted to crop biomass by the
intercrop as a result of differences in competitive ability for growth factors between intercrop
components. Efficient utilization of growth resources leads to yield advantages and increased
yield stability compared to sole cropping. The multifunctional profile of intercropping allows it
to play many other roles in the agro ecosystem, such as resilience to perturbations to weather,
protection of plants of individual crop species from their host-specific predators and disease
organisms, greater competition towards weeds, improved product quality and reduced negative
impact of arable crops on the environment, nitrogen fixing legumes can be included to a greater
extent in arable cropping systems via intercrop.
Inorganic fertilizers have the advantage of delivering nutrients more readily and directly to
plants but are prone to leaching, burning of seedlings by desiccation and build up of toxic
concentrations of salts that can create chemical imbalances. Fertilizers applied should provide
easily available plant nutrient forms on soils which are highly leachable and low in organic
matter, therefore, K20 should be applied preferably in the Sulphate form. It was found that to
produce a ton of grains, the following elements will be required: 65 kg N, 11kg P205, 20 kg K20,
4 kg Mg0, 4 kg Ca0, 2 kg S, 110 kg Fe, 33 kg Mn, 43 kg Zn, 16 kg Cu; 16 kg B, 6 kg Mo
(Bataglia and Mascarenhas, 1978). Balanced fertilization for sustainable agricultural production
and nutrient consumption in developing countries is nowhere near to the ideal ratio of 4:2:1,
nitrogen, phosphorous and potassium, which poses a serious threat to soil K and soil health
(Samra, 2007).
Nitrogen (N): Soybean as a legume can fix large quantities of atmospheric N to produce yields
of 3000-4000 kg/ha, if nodules formed well. Johnson et al. (1975) found that adding N to well
nodulated soybeans did not increase yield. Fertilizer N added at planting delays nodulation.
Gasscho et al. (1989) suggested that N application during the vegetative stages result in decrease
in nodulation in proportion to the rates applied. Adding N is recommended only when adequate
nodulation is not expected. One ton of soybean seed removes 60 kg of N by the plant, or about
270 kg N for a 3-ton seed crop. Nitrogen need not be applied if the crop is well inoculated with
4
bacteria. Where inoculation is poor, N fertilizers should be applied at the same rate as maize
(Smith, 2006). N deficiency results in reduced chlorophyll development (pale-green leaf), growth
and yields.
Phosphorus (P): is absorbed by plants throughout the growing season and its availability is at
maximum level at a pH of between 6.0 and 7.0. Adequate P is essential for optimal crop yields,
enables a plant to store and transfer energy, promotes root, flower and fruit development and
allows early maturity in plants (Elliott et al., 2009). The period of greatest demand for
phosphorus starts just before the pods begin to form and continues until about 10 days before the
seeds are fully developed. Much P used in seed development is taken up early, stored temporally
in leaves, stems and petioles, and then trans-located later into the seed. Stunted growth is usually
the only symptom of P deficiency, though some leaf cupping and discolouration are possible.
One ton of soybean seed removes 5 kg of P, compared with 3 kg of P for maize. Being a lower
yielder, soybeans would remove 70 % of the P contained in a maize grain crop. Soil with
medium or low levels of P would benefit with the application of 20-40 kg/ha. Optimum P for
loam soil is 22 mg/litre and 12 mg/litre for clay. P tends to move downhill across the field and is
less likely to leach vertically into the ground water. On alkaline soils, it is best to use composted
or vermicomposted manure to minimize environmental impacts (Elliott et al., 2009).
Potassium (K): Relatively large amount of K are required for growth. It has been reported that
rate of uptake is highest during rapid vegetative growth and slows down as seed formation
begins. Uptake continues until two to three weeks before the seed is mature. K uptake can be
depressed by poor soil condition, including compaction, excess moisture and poor aeration. Most
K taken up, moves to the roots by diffusion through moisture films around soil particles. As the
water content of a soil decreases, moisture films around the soil particles become thinner and the
path length of K ion movement increases and the movement of K to roots decreases. Potassium
uptake is reported to decrease if the oxygen content of the soil is low, therefore poor aeration
would require higher available K, while cold soils reduce the rate and extent of root growth
which further limits K uptake. When farmers plant earlier or adopt tillage practices such as notill
that result in reduced soil temperature early in the growing season, higher levels of available
K in the soil are likely to be needed for optimum growth (Yin and Vyn, 2001; Isherwood, 2006;
Magen, 2007). One ton of soybeans contains 18 kg of K compared with 3.5 kg K for maize grain
5
and will remove twice the amount of K as maize grown under similar conditions. Five tons of
maize compared with two tons of soybeans. Soil test result of 80 mg/litre for soybean is the
critical level at which point K application is required. Soils with medium or low levels of K
should receive 30-60 kg/ha of K. K deficiency is easily recognized by chlorosis which starts
along the outside edges of leaves and moves inward, especially in the older leaves.
Liming: Soil acidity has been recognized as one of the major limiting factors to the production
of legumes and many other crops (acidity fixes most soil nutrient elements), hence liming is
needed on acidic soil surface for optimum or maximum yields (Prince, 1956, Duong, 1986,
Lickacz, 2002). Lime is applied to acid soils to neutralize excess acidity (very low pH) that
causes reduced crop yields. Lime application raises soil pH, making the soil more productive in
several ways. 1) Liming removes aluminum and iron toxicity to growing plants by making them
insoluble. 2) Liming keeps phosphorus of the soil and in applied phosphates in available forms
over a longer period. 3) Calcium salts in lime promote flocculation or granulation hence
limestone improves soil structure, better aeration and water relations and making the soil
environment more suitable for plants to grow. 4) Liming increases the activity of nitrogen fixing
organisms, hence an important practice in legume production. 5) Liming promotes more rapid
decomposition of manure and crop residue in the soil, thus making elements contained in them
more readily available to the plant.
Wood ash: The beneficial effect of wood ash on crop growth as an alternative to lime and/ or to
the use of acidity tolerant crops has been documented (Duong, 1986, Spore, 1995, Lickacz,
2002). It is the inorganic and organic powder residue left after the combustion of wood or
unbleached wood fibre which contains the oxides and hydroxides of calcium, magnesium,
potassium and to a lesser extent sodium. It is similar to burned or hydrated lime in its mode of
action (Lickacz, 2002). It has been used to supply calcium in groundnut plots showing calcium
deficiency (Spore, 1995). Many factors contribute to soil acidity such as, acidic rock parent
materials, leaching, crop removal at harvest, use of nitrogen fertilizers, decomposition of soil
organic matter, plant root and soil organism respiration, presence of deciduous and coniferous
vegetative cover and absorption of carbon dioxide and sulphur directly from the atmosphere.
6
Organic fertilizers: Organic fertilizers such as animal or plant residue manure have the
limitation of taking a little longer to break down in the soil, but they improve the soil structure,
increase the ability of soil to hold both water and nutrients and the risk of toxic build up of
nutrient is minimal. Concerns for environmental quality have necessitated the use of livestock
manures in fields planted to soybean crop rather than applying excessive amounts on lands where
maize is grown, because such manures are excellent sources of nitrogen (N), phosphorus (P),
potassium (K), all secondary nutrients and the micronutrients (Rehm et al., 2010). They also
stated that organic fertilizers come from animal manures including, compost and sewage sludge.
Generally chicken (poultry) manure is the best, followed by goat manure while cattle manure is
of lower quality (ICRISAT/MAI, 2000).
The Soybean Crop
Soybean has been proved to be an excellent source of food for man and very ideal as infant foods
as it has minimal oligosaccharides which cause flatulence in other grain legumes. Its oil content
belongs to the linolenic unsaturated fatty acid group without cholesterol (Rehm and Espig,
1991). Soybean is also used in crop rotation for soil fertility restoration as it leaves the soil
friable and easy to plough and is an excellent crop to grow in rotation with maize, cotton,
sorghum or winter wheat. Soybeans could increase the grain yield of the succeeding crops of
maize or wheat by 1.3 t/ha (Smith, 2006). According to Sanchez (Spore, 2003), maize yields
increased by a factor of 2-4, and almost attained the levels achievable by applying recommended
rates of N fertilizer
The Maize crop
Maize (cereals) and legumes are agronomic and gastronomic complements. Cereals intercropped
or planted after legumes in a rotation utilize the nitrogen fixed by legumes to satisfy their
nitrogen needs. Cereals are rich in methionine and cystine but deficient in lysine and tryptophan
contained in legumes but low in methionine and cystine. These deficiencies can be balanced by
their combination in a diet with 1/3 beans and 2/3 maize which gives a biological value (BV) of
100 similar to a hen’s egg used as a standard (Rhem and Espig, 1991, Kaldy, 1972). According
to Daramola (1993), maize has already been integrated into the cropping systems of the rural
farmers in most parts of Africa and is the most important cereal in the rainforest and derived
7
Savanna zones of Nigeria usually intercropped with cassava and/ or yam by the smallholder
farmers.
Studies on sustainable ways of managing soil fertility status for improved crop production and
food security have engaged the research efforts of agricultural scientists and food policy makers
in the recent years as human population is rapidly increasing while food production is lagging
behind particularly in the Sub-Saharan Africa. Postgate (1970) indicated that biological nitrogen
fixation is still the rate determining step in crop production and soil fertility restoration in
tropical Africa, while Leinonen (1996), observed that though legumes have high potentials to
rehabilitate degraded soils, the rate of nitrogen fixation is dependent on the vigour of the plant,
efficiency of the rhizobia and environmental conditions of the legume crop. Giller (2003)
however, observed that despite more than a century of research on green manures in the tropics,
examples of smallholder farmers using such methods to regenerate their soils are remarkably
rare, because farmers tend to prefer grain legumes (pulses) with rich economic food value
beyond simply improving soil fertility. Against this background was the choice of soybean – a
versatile legume with high quality edible oil, very superior protein, a good source of
carbohydrate and a benchmark nitrogen fixing legume – implicated in an area without any
history of soybean cultivation.
Objectives:
Therefore, the aim of this study was to address the following specific objectives:
1. To evaluate the growth and yield performances of twelve IITA promiscuous (naturally
nodulating) soybean varieties in Abakaliki climatic condition,
2. To determine the effect of some soil fertility management options on the growth and
yield of soybean and maize varieties in Abakaliki, and
3. To assess the fertilizer replacement value (FRV) of soybean varieties to non-legume
intercrop and subsequent non-legume crops like maize
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