1.0 INTRODUCTION
Pearl Millet (Pennisetum
glancum (L.) R. Br.) and sorghum (Sorghum
bicolor L.) Moench) are the major subsistence arable cereals in the
Sudano-Sahelian zone of Nigeria (Ikwelle, 1998). They are the staple food for
millions of people in the area. The stalks are serves as fodder for feeding
livestock especially during the dry season. Resource-poor people in the rural
area also use the stalk for constructing houses and as fuel (ICRISAT, 1992,
LCRI, 2007).
Although over 10 million hectares are under millet and
sorghum cultivation, the productivity is low. Farmers’ yields of millet range
between 944 and 1076 kg ha-1 and that of sorghum between 1021 and
1144 kg ha-1 (FMARD 2005; Yusuf and Yusuf 2008). These yields are
far below the yields potential of these crops. Researchers have shown that
under improved agronomic management practices, sorghum can produce grain yield
of 4000-5000 kg ha-1
and millet 2000-3500 kg ha-1 (FPDD, 2002).
Soil fertility is one of the major threats to crop
production in this zone (Chude, 1998). Rayar (2000) showed that majority of
soils in Sudano-Sahelian region are inherently low in fertility and marginal in
their productivity. This might be attributed to the dominant sand fraction of
soils, and low turnover of plant residues which is due mainly to low rainfall
and human and livestock activities coupled with wide spread of wind and water
erosions. Another cause of low fertility is nutrient mining and poor agronomic
management practices by resource poor farmers (Yusuf and Yusuf, 2008). Nutrient
balances are negative for many cropping systems indicating that farmers are
mining their soils. They annually remove large quantities of nutrients from
their soils without returning them as manure or fertilizer in sufficient
quantities. Consequently, a sustainable crop production could be achieved by
application of chemical fertilizers and animal manure to replenish the depleted
soil nutrients and increase the organic matter content of the soils as reported
by Kwari and Bibinu (2002).
The use of inorganic fertilizers to overcome declining
soil fertility in the sub-Saharan Africa is however limited by the economics
conditions of resource-poor farmers who are the majority in the region
(Drechesel and Gyiele, 1999). Animal manures are inadequate in supply because
the greater proportion of livestock feed on extensive range land where manures
are difficult to collect. Another limiting factor is the cost of transporting
manure to farms as farms are getting further and further away. The other option
is the use leguminous green manure crops as soil amendment to address the soil
fertility problem (Muhamman and Gungula, 2006; Valauwe and Giller, 2006).
Studies conducted in the tropics by Agboola, 2000; Olabede
et al., 2007; Abubakar, 2009; and
Fening et al., 2009, showed that
incorporation of leguminous green manure crops into the soil significantly
increased the soil organic carbon, available N and P, exchangeable K, Ca and
Mg; micronutrients, water holding capacity, nutrient use efficiency and crops
yields. In addition, the use of green manure is cheap and cost effective with
high monetary return. Economic analysis of effect of green manure on sorghum
and rice production showed that the treatment had a high cost-benefit ratio
(Abubakar, 2009; Kayeke et al.,
2007). However, the effectiveness of green manure crops varies with species and
environmental conditions (Muza, 1998; Kayeke et al., 2007). Some of the promising species of leguminous green
manure crops in the tropics are Mucuna
pruriens, Dolichos lablab, Centrosema pubescens, Sesbania rostrata, Cajanus
cajan and Canavalia ensiformis.
They are good N-fixers, high biomass producers, drought-tolerant and grow well
in very poor soil (Bunch, 2010; Cherr et
al., 2006; Abubakar, 2009). It is therefore, expected that these green
manure crops will perform well in Borno State.
Even though sorghum
and millet are the dorminant cereals in this region, information on the effect
of green manuring on their yields is scanty. Therefore, more information is
needed to determine which green manure crop species hold promise on the
performances of these cereal crops.
1.1 STATEMENT OF THE PROBLEM
In Sudano-Sahelian
zone of north-eastern Nigeria sorghum and millet are the dorminant cereals, but
their yields are low mainly due to low soil fertility. Fertilizers are
expensive, and animal manure is inadequate in supply. There is very little
information on the effects of green manuring on these cereal crops. This calls
for identification of suitable green manure crop species to improve the soil
fertility and yields.
1.2 OBJECTIVES OF THE STUDY
The objectives of this study are to:
(i)
determine
the NPK content in 15 green manure crop species;
(ii)
identify
the best six green manure crops species to be used in sorghum and millet
production;
(iii) investigate the effects of the selected
species on the growth, yields and nutrient uptake by the sorghum and millet;
(iv) investigate the effects of the selected green
manure crop species on the soil chemical properties, and
(v)
evaluate
the cost-benefit ratio of green manuring in sorghum and millet production, with
a view to identifying the most cost effective species in this agro-ecological
zone.
1.3
SIGNIFICANCE OF THE STUDY
This study will provide information on:
-
which
leguminous green manure crop species will increase the yields of millet and
sorghum;
-
which
leguminous green manure crop will improve the soil fertility;
-
the
economic benefits for using the leguminous green manure crops in production of
millet and sorghum in Borno State.
Such
information will be used by farmers, researchers and policy makers for
developing sustainable millet and sorghum production systems in Borno State.
1.4 SCOPE OF
THE STUDY
This study will involve a pot experiment in a screen house
and two-year field experiment to be conducted during 2012 and 2013 cropping
seasons in Mohamet Lawan College of Agriculture, Maiduguri and Damboa Local
Government farm. Fifteen (15) species of green manure crops will be screened
for their N, P, and K contents and the best six species will be selected. The selected species will be tested on
millet and sorghum under field conditions. Grain yields, nutrient uptake by the
crops, soil chemical properties and cost-benefit ratio will be analysed.
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Soils of the Savanna Region in Nigeria
The Savanna region of Nigeria is occupied by Entisols,
Alfisols, Inceptisols and Vertisols soils mostly derived from aeolian,
lacustrine, lagoonal and alluvial deposits and basement complex (Lombin 1987;
Nwaka 1991). Entisols and Alfisols occupy most of the landscape in the
Sudano-Sahelian zone. Entisols are mostly composed of quartz sand, with low
water and nutrient holding capacity. Alfisols have a clay accumulation horizon
and a high base saturation because of lower rainfall and leaching but they have
poor structural stability, poor water and nutrient holding capacity and lower
organic matter than the Ultisols and Oxisols in the sub-humid areas (Bationo et al., 2003).
One striking feature of these soils is their inherent low
fertility which is expressed in low levels of organic carbon (generally less
than 0.5%) low total and available phosphorus and nitrogen and low Effective
Cation Exchange Capacity (ECEC) (Bationo et
al., 2003; Rayar 2000). The ECEC is attributed to low clay and organic
matter content and the kaolinitic mineralogy of the soils. Bationo and Mokwunye
(1991) found that the ECEC is more related to the organic matter than to the
clay content indicating that a decrease in organic matter will decrease the
ECEC and then the nutrient holding capacities of these soils. The low organic
matter might be due to low turnover of plant residues which is attributed
mainly to low rainfall and human and livestock activities coupled with
widespread wind and water erosions.
The problem of low fertility of the soils is further
accelerated by nutrient mining from the soils by the farmers. Nutrient inflows
are less than outflows. Famers annually remove large quantities of nutrients
from their soils without returning them as fertilizers or manure in sufficient
quantities and this has caused negative nutrient balances in many cropping
systems (Yusuf and Yusuf, 2008). Soil nutrient depletion is a major bottleneck
to increased land productivity in the region and has largely contributed to
poverty and food insecurity.
2.2 Options for improving soil fertility in
savanna region of Nigeria
The use of inorganic fertilizers improves soil fertility
status and crop productivity very fast. But poor economic conditions of small
scale farmers who are the majority in this region limits the use of mineral
fertilizers (Drechesel and Gyiele 1999). The integration of farmers available
organic resources in their cropping systems is therefore being regarded as
alternative to inorganic fertilizers. Farmer available organic resources such
as cow dung, sheep dung and poultry manure are however inadequate in supply
(Kwari, 2003). The greater proportion of livestock feed on extensive range land
where manure is difficult to collect. Crop residues also have alternative uses
as fodder, fuel and building materials for which there are often no substitutes
(Quedraogo et al., 2005). The other
option is the use of high biomass producing plants (green manure) as soil
amendment to address the declining soil fertility under continuous cropping
systems (Vanlauwe and Giller, 2006).
2.3 Uses of Green Manure
A green manure is a crop used primarily as a soil
amendment and nutrient source for subsequent crops. Green manure approaches to
crop production may improve economic viability, while reducing the
environmental impacts of agriculture (Cherr et
al., 2006). Green manures grown on site do not incur the often inhibitive
handling and transportation costs. The slow release of N from decomposing green
manure residues may be better synchronized with plant uptake than sources of
inorganic N, possibly increasing N-uptake efficiency and crop yield while
reducing N leaching losses (Abdul-Baki et
al., 1996; Aulakh et al., 2000). In
addition, other nutrients are also released in to the soil (Onwu et al., 2006). Green manure approaches
may also drive long-term increases of soil organic matter and microbial biomass
(Goyal et al., 1999; Biederbeck et al., 1998; Fening et al., 2009), further improving
nutrient retention and N-uptake efficiency. When used in place of fallow,
well-chosen green manures may reduce erosion (Dapoah and Vyn, 1998), reduce
nutrient or pesticide losses (Delgado et
al., 2001; Gaston et al., 2003),
and suppress weeds (Dyck and Liebman, 1995; Burgos and Talbert, 1996) and
specific crop pests (Caswell et al.,
1991). Green manures may also offer habitat or resources for beneficial
organisms (Nicholls and Altieri, 2001).
2.4 Required Characteristics of Green Manure
Crops
Studies conducted by Skerman et al., (1998) and Carsky et
al., (2000) showed that a good green manure crop must possess the following
characteristics.
-
It
must be nonwoody annual with vigorous growth and high biomass production.
-
It
must be able to grow on very poor soils without any amendment,
-
It
should be easy to establish without any special preparation,
-
It
should be drought tolerant and pest resistant,
-
It
should be shade-resistant in
intercropping,
-
It
should be able to fix atmospheric nitrogen,
-
It
should be economically viable and environmentally safe.
Generally, green
manure approaches to crop production are complex because they depend on
interactions between the green manures, the environment, and management. Therefore,
there is a need for a proper understanding of the site specific relationships
between the life cycles of the plants used (both green manure and subsequent
economic crops), the production environment (climate, soils and pests), and
management options (for example: type and timing of tillage, planting,
irrigation, and fertility and pests control inputs, as well as production
goals) (Cherr et al., 2006).
2.5 Green manure relationships with
environment and management
Climate probably limits green manure species selection
more than any other single factor. Temperate legumes often decline at temperatures
above 25-300C but may persist without injury at -100C or
below. Tropical legumes, on the other hand, can’t survive when temperature
drops below -200C for several hours, although they can usually
tolerate temperatures 35 to 400C. The most widely used tropical
green manure legumes probably include Crotalaria
juncea, Mucuna pruriens, Dolichos lablab, Sesbania sesban, Sesbania rostrata,
Peuraria phaseoloides (Cherr et al.,
2006; Onwu et al. 2006). In Nigeria
some of the promising green manure crops include Sesbania rostrata, Chromoleona odorata, Mucuna pruriens, Centrosema
pubescens, Stylocanthes guianeensis, Tithonia diversifolia, Calopegonium
mucunoides, Peuraria phaseoloides, and woody legume prunings of Sesbania sesban, Leucaenia leucocephala
and Gliricidia sepium (Mulongoy and
Nguu 1989; Fagbenro 2000; Obatolu and Agboola, 1993; Olabode et al., 2007; Abubakar, 2008).
Genetic differences (species and variety) may dictate that
some legumes grow larger and accumulate more N than others. Environment
(temperature, soil type and nutrient water availability) and management
(planting, density and timing, and pest control) may further alter performance
of individual green manure species (Kouyate et
al., 2000; Steinmaier and Ngoliya, 2001). Biological N fixation and overall
N accumulation during growth are primary factors governing the adequacy of a
green manure as an N source. Generally speaking, most legumes accumulate N from
biological fixation when demand cannot be met by uptake of N from the soil (Gardner,
1985). For example, Sunhemp (Crotalaria
juncea L.) has been estimated to fix 27 to 39% (Ramos et al., 2001), 72 to 81% (Ladha et
al., 1996), and 91% (Seneratne and Ratuasinghe, 1995) of its total N in
different study locations and conditions. Reduction of soil N through
competition generally increases rates of biological N fixation by legume.
Kerpenstein-Machan and Stuelpnagel (2000) found greater N accumulation for optimal
mixtures of legumes with cereal rye than legumes alone. However, water stress
and deficiency of nutrients other than N may significantly reduce fixation
(Gardner, 1985).
Green manure performance and patterns of subsequent
effects often differ based on gross differences in soil textural type. Green
manure growth and N accumulation are usually greatest on loamy soils due to
their relatively high inherent fertility, nutrient and water retention
capacity, and microbial biomass (Cherr et
al., 2006). With their high potential to retain released N, such soils also
help mediate short-term benefits from green manure to subsequent crops, even
when considerable long times exist between peak N release (from decomposition)
and subsequent crop N uptake. On sandy soils and in warm, humid climates, even
short long times between peak green manure N release and subsequent crop N
demand can result in significant leaching losses (Nelson and King, 1996;
Weinert et al., 2007).
2.6 Effects of leguminous green manure crops on
yield and yield parameters of millet and sorghum
Application of green manure improves yield of crops
through provision of favourable soil conditions to the crops. Green manuring
with an N2-fixing legume crop can meet a substantial portion of N requirement
of economic crops and increase their yields. The use of various leguminous
green manures in rotation with sorghum in north-eastern Nigeria drastically
increased yield from 1,809 Kgha-1 under control to 3,089 Kgha-1
in the green manure (Lablab) treated plot (IAR, 1999). Study conducted in
semi-arid region of Nigeria by Kwari, (2003) showed that application of green
manure of Sesbania rostrata increased
the straw and grain yields of millet by 24.4 and 23.3%, respectively, over the
control. In the same region, Sesbania
rostrata incorporated at 6 weeks after
sowing increased the straw and grain yields of sorghum by 63 and 129%,
respectively, when compared with untreated plot (Abubakar, 2009).
Fening et al.,
(2009) evaluated the contributions of three green manures to maize yield in the
semi-deciduous forest zone of Ghana and reported that application of 3 t ha-1
of the manure increased the maize yield between 49.1 and 57.4% when compared
with the control. The highest yield increase (57.4%) was obtained from crops
treated with green manure of Crotolaria
juncea. This variation is due to the difference in chemical composition of
the green manures applied to the soil and mineralization aspect controlled by
the C:N ratio. Similarly, the results of four years studies in Spain (Tejada et al. 2008) showed that application of
green manure of Trifolium pratense,
L. at the rate of 5.384 kg Cha-1 increased the grain protein
concentration, number of grains corncob-1 and maize yield by 44.6,
6.3 and 22.1%, respectively, when compared with the control soil.
The effects of green manures of Crotolaria ochlralenca G. (sumheanp), Mimesa invisa L. (Colla) and Cassia
obtusipoila L. (Sickle pod) on the performance of upland rice in Tanzania
were evaluated (Kayeke et al., 2007).
The results showed that number of panicles per plant, panicle length and grain
yield were significantly higher in manured plots than the control. The green
manures differed significantly in their influence on the performance of rice.
They were in the order of C. ochlralenca
> M. invisa > C. obtusifolia. Green manuring with an N2
– fixing legume crop can meet a substantial portion of rice N requirement and
significantly increase the grain weight (Latt, et al., 2009).
According to Onwu et
al., (2006), application of 40 tha-1 of green manure of Calopogonium mucunoides increased the
plant height and grain yield of Castor by 42.2 and 71.3%, respectively, over
the control in Guinea Savanna of Nigeria. In contrast, Pilipenko and
Savoshdenko (1998) reported that application of green manure had not
significant effect on barley production. Nutrient availability in the right
quantities, ratios and in synchrony with crop demand is important for good crop
yields.
Generally leguminous green manure crops outperform their
nonleguminous counterparts because of their narrow C:N ratio which makes them
easily mineralizable and supply nutrients in synchrony with economic crops
demands.
2.7 Effects of leguminous green manures crops
on nutrient uptake by plants
Application of green manure improves soil organic matter
status, which leads to a higher water – holding capacity and root growth which ultimately
increase nutrients uptake by the plants. Organic matter increase the
availability of unavailable plant nutrients by enhancing the biochemical
activity of microorganisms. Hortentine and Rothwell, (1969) reported that
addition of compost at 5.2 tha-1 resulted in the extraction of 5
times K by millet crop when compared to control. According to Tejada at al., (2008) application of green
manures of Trifolium, pratense L. and Brassica impus L. to maize plant in an Typic xeroflurent soil at
high doses increased the grain protein concentration by 46.6 and 39%,
respectively, over the control.
A significant increase in N uptake by wetland rice due to
incorporation of Sesbania rostrata
green manure was reported by Latt et al.,
(2009). Similarly, a positive effect of Sesbania
rostrata green manure on N, P and K uptake by sorghum plant in semi-arid
region of Nigeria was reported by Abubakar, (2009). The highest uptake of N
(16.6 Kgha-1) and P (5.8 Kgha-1) were recorded in the parnicle
while that of K (52.7 Kgha-1) was found in the straw, when compared
with control.
A three years study conducted in dryland zone of Turkey
showed that application of rye green manure to wheat plant increased Fe, Mn and
Zn uptake by 48, 31 and 16%, respectively, but decreased P and Cu uptake by 8
and 3%, respectively, over the control (Masori et al., 2008). The increases in nutrients uptake might be due to
the microbial release of the nutrients from the manures and also due to the
action of organic acids produced from the decomposing manures which helped in
the release of native minerals bound in insoluble forms.
2.8 Effects of leguminous green manures on the
soil chemical properties
Ploughed – in leguminous green material enriches soil with
organic matter, which as a result of microbiological processes releases
nutrients for plants. It also ameliorates soil’s physical and chemical
properties (McGuire et al., 1998).
Similarly, Bunch (2010) reported that green manuring increases the levels of
soil organic matter, and this has a whole series of positive effects on the
soil, such as improving its water – holding capacity, nutrient content,
nutrient balance, friability and pH.
Schomberg et al.,
(1994) reported that addition of organic matter to the soil buffers the soil to
an extent, thereby bringing an increase in the negatively charged ions which
consequently increases the pH level and cation retention by reducing KCl –
extractable Al. According to Parkins at
al., (1964) green manure on decomposition releases organic acid which acts
as solubilitizing agent for calcium and thereby improving the acidity. Nwosu
and Chukwu (2009) reported that some leguminous cover crops including mucuna
and stylozanthes exhibited over 20% liming potentials in acid soil of
south-eastern Nigeria. Similarly, Abunyewa et
al., (2004) observed significant increases in soil pH and electrical
conductivity as a result of incorporation of green manures. In contrary, Kwari et al., (2004) recorded 4.3% decrease in
soil pH due to application of Sesbania green manure in semi-arid region of
Nigeria.
Study conducted by Abubakar (2009) showed that application
of Sesbania green manure at 8 weeks after planting to soil under sorghum
increased the soil pH, electrical conductivity (EC), organic matter, total N,
available P, exchangeable K, Ca and Mg and ECEC by 5, 33, 77, 13, 60, 67, 31,
224 and 42%, respectively, over the control. Similarly, incorporation of 40 tha-1of
green manure of leguminous weed (Celopogonium
mucunoides) to soil under castor
plant increased the organic matter, total N, available P and exchangeable Ca
and Mg of the soil by 20, 19, 31, 92 and 40% respectively, when compared to the
control (Onwu et al., 2006). Conversely,
application of rye green manure to wheat plant in dryland zone of Turkey
decreased the soil organic carbon, available P, total N, available Fe, Cu, Mn
and Zn by 11, 20, 12, 3, 6, 13 and 5% respectively, when compared to the
control (Mosari et al., 2008).
2.8.1 Green manure management
Nutrients release from plant residues depends on a large
number of interactive factors including chemical composition and N
concentration, temperature, and water availability (Schomberg et al., 1994). Decomposition and
nutrients release generally occur faster for residues with lower C/N ratios and
lignin and polyphenol contents (Brady and Neil 2002). Prolonged periods of N
immobilization are often recorded for recalcitrant stems and roots (Cobo et al., 2002).
Soil incorporation of plant residues may speed
decomposition and N release by buffering temperature and water regimes relative
to the surface (Thonnissers et al., 2000). Schomberg et al., (1994) found greater N
immobilization potential for sorghum and wheat residues on the soil surface,
although initial N immobilization was more rapid when the residues were buried.
Optimum temperature and water availability for soil-based
decomposition are usually around 350C and field capacity, respectively
(Lomander et al., 1998). Green manure
N release can occur before (generally in warmer environment; Sainju and Singh,
2001) or after (generally in cold environments; Shrestha et al., 1999) peak N demand from subsequent crops.
Growth management may also exert effects on green manure
residue quantity and quality. Generally, leaf tissue fractions dominate shoot
during early season growth while stems become increasingly important as time
goes on (Cherr, 2004). Low plant population may increase the proportion of
green manure as stem or lignin, while higher plant population may favour greater
leaf and non-structural carbohydrate production (Marshall, 2002) especially in
organic matter with upright growth. High plant populations may facilitate early
season production with earlier canopy closure. In these cases, manipulation of
residue quality through proper selection of green manure, and planting
densities, tillage and timing may better synchronize leguminous green manure-N
release with subsequent crop demand.
2.8.2 Six-step checklist to assess potential green
manure use in cropping systems
Considering the importance of green manuring in
sustainable crop production, it is necessary to have a framework for assessing
potential green manure use. Cherr et al.,
(2006) proposed a six-step checklist to assess potential green manure use in
cropping system: -
(i)
Determine
pre-existing environmental factors that will affect green manure function:
-
Climate:
temperature ranges and seasonality; rainfall amount and distribution; light
levels.
-
Soil
texture, fertility, organic matter, and pH.
-
Important
pest, disease, and weed pressures that may affect green manure and economic
crops.
(ii)
Determine
pre-constrained management factors that will affect green manure function:
-
Choice
of economic crop and its requirements for optimal stand establishment and
growth.
-
Use
of irrigation, fertility, or pest control inputs.
-
Identify
tillage/residue management approaches.
(iii)
Determine
desired services from green manure:
-
N
supply for subsequent crop
-
Reduce
soil erosion
-
Build
soil organic matter.
-
Reduce
leaching losses of residual N from previous crop.
-
Provide
seed, forage, or other economic product.
-
Pest,
disease or weed suppression.
(iv)
Evaluate
effects of pre-existing environmental factors and pre-constrained factors on potential
growth and decomposition of candidate green manure species:
-
Evaluate
adequacy of soil moisture for acceptable green manure stand establishment.
-
Consider
how actual environment and growth time may alter green manure biomass and N accumulation
potential compared to values reported in other environments.
-
Assess
expected rate of green manure decomposition and N release.
(v)
Evaluate
potential of candidate green manure to provide desired services given the
environment and management:
-
Will
the amount and timing of green manure N release match subsequent crop N demand?
Can soil adequately retain N in the crop rooting zone under expected
precipitation?
-
Will
green manure take up residual soil N prior to leaching events?
-
Does
green manure make adequate residue contributions to the soil to increase soil
organic matter?
-
Will
green manure suppress/reduce the problem pests, disease, or weeds that affect
economic crop? For what time and/or over what distance will
suppression/reduction occur?
-
Does
green manure biomass provides adequate soil coverage to reduce erosion?
-
If
green manure is cut for forage, or harvested for seed, can it still provide
other desired benefits?
-
In
intercropped systems, will unacceptable competition between green manure and
economic crop be avoided?
(vi)
Evaluate
what additional aspects of management are required to obtain desired services
from candidate green manure.
-
Additional
irrigation, fertility, and pest/disease/weed control inputs.
-
Change
in tillage or green manure residue management.
-
Alter
green manure or economic crop planting date or rate.
-
Change
in economic crop species or varieties.
2.9 Economic analysis of green manure
Use of green manures in crop production may give a
considerable economic benefit. However, the economic viability of green manure
based systems depends on externalities and internalities (Dobbs, 2004). Farmers
(and researchers) have no direct control over factors external to their
operations. For example, in areas where mechanization is not possible, green
manure approaches with high labour requirements for planting and residue
management may become too costly, especially where synthetic fertilizers are
inexpensive (Rao and Mathuva, 2000).
Internally, a particular approach to crop production will
affect economic profit and risk. Farmers may also have to consider input,
transition, and opportunity costs associated with green manure (Ali, 1999).
External factors aside, green manure approaches are often found to be
economically superior to chemical-based approaches when capable of providing
multiple services (Ali 1999), when green manure replaces costly conventional
inputs such as fallow management or plastic mulches (Ellis et al., 2000), when one or more species from multispecies green
manure mixtures serves as an economic crop (Ghaffarzadeh, 1997), and when
strict green manure crops are replaced with crops that provide food or feed
while residue is left in the field (Ali, 1999). Use of green manure may have
higher cost-benefit ratio than that of inorganic fertilizers. Cost-benefit
ratio (CBR) which can be defined as the total discounted benefit divided by the
total discounted cost (Kruse, 2004) is an important parameter since it
determines the viability of a project. Abubakar, (2009) reported a higher
economic returns in using Sesbania
rostrata green manure at 6 weeks after planting than chemical fertilizer
NPK (60-30-30) kgha-1 for sorghum production in Sudano-Sahelian zone
of Nigeria. Similarly, a study conducted in Tanzania on the effects of green
manure crops and inorganic fertilizer on upland rice (Oryza sativa) showed that the benefit per unit cost incurred was
higher in treatments with green manure applications. The cost-benefit ratio varied
depending on the green manure species with (Crotolaria
ochlroleuca) having the highest (Kayeke et
al., 2007). In contrast, Channbasappa et
al., (2005) did not observe significant difference in cost-benefit ratio
due to application of seven different green leaf manures to rice.
CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Pot Experiment
A pot experiment will be conducted in a screen house
at Mohamet Lawan College of Agriculture, Maiduguri in 2012 rainy season. The
treatments will consist of 15 species of green manure crops namely;
1.
Crotalaria juncea
2.
Centrosema pubescens
3.
Stylocanthes guianeensis
4.
Calopogonium mucunoides
5.
Peuraria phaseoloides
6.
Mucuna pruriens
7.
Sesbania rostrata
8.
Sesbania sesban
9.
Canavalia ensiformis
10.
Trifolium incanatum
11.
Aesehynonene histrix
12.
Mucuna rajada
13.
Chamaecrista refundifolia
14.
Carjanus cajan
15.
Dolichos lablab
Top soil (0-15 cm)
will be collected from fallow land in the college, air dried and sieved through
a 2 mm screen. The seeds of green manure crops will be scarified by soaking in
boiled water for a minute and dried before sowing Three kilograms of the soil will
be placed in each plastic pot and four seeds will be evenly sown per pot. The
treatments will be replicated three times and arranged in completely randomized
design. The seedling will be thinned down to two a week after emergence. The
plant will be irrigated whenever there is dry spell.
At six weeks after
sowing, the plants will be harvested by cutting the shoots at soil surface
levels and the roots will be removed and washed with distilled water. The plant
materials will then be oven-dried at 650C for 48 hours and their dry
matter weights will be measured.
3.1.1 Plant Analysis for N, P, and K elements
The nitrogen, phosphorus and potassium contents of the
plant materials will be determined using single acid digestion method as
described by IITA (1979).
3.1.2 Data Analysis
Data collected will be subjected to analysis of variance.
Duncan Multiple Range Test (DMRT) will be used to separate the means that are
significantly different. The best six green manure crop species will be
selected for further investigations.
3.2 Field Experiments
Two years field experiments will be conducted in rainy
seasons at Mohamet Lawan College of Agriculture Farm Maiduguri and Damboa Local
Government Agriculture Farm. Maiduguri
is located between latitude 110 51’ and 130 40’N and
longitude 100 14’ and 140 E and altitude of 352 m above
sea level (Kowal and Knabe, 1972), in the Sudan savanna of Nigeria. The
rainfall distribution is unimodal, starting on average, in mid-June and lasting
until the end of September (Grema and Hess, 1994). The mean annual rainfall at the site (1992-2007) was 640 mm
(Abubakar, 2009). The vegetation consists of mainly savanna grassland and
suffers severely from desert encroachment. The major soil types found in
Maiduguri include entisols and inceptisols derived primarily from the recent
Aeolian sand deposits of the Sahel Savanna. Thus, the soils are characterized
by sandy texture with low organic matter content, low CEC and inherent low
fertility status (Rayar, 2000). Millet and sorghum are the dominant cereal
crops in the area.
Damboa is located in Southern Borno and falls in the
Northern Guinea savanna with the mean annual rainfall of 831 mm. The soils are
mainly Gleyic Luvisol, loam in texture (Rayar 1987). Sorghum and millet are the
major cereal crops cultivated in the area.
3.2.1 Treatments and Experimental Design
Treatments comprising six most promising leguminous green
manure crops (identified in pot experiment), NPK recommended rates and control
will be tested under two sets of experiments involving cereal crops of millet
and sorghum in Maiduguri and Damboa. There will be sixteen treatments for each
set of experiment as follows:
T1 = MGm1
T2 = SGm1
T3 = MGm2
T4 = SGm2
T5 = MGm3
T6 = SGm3
T7 = MGm4
T8 = SGm4
T9 = MGm5
T10 = SGm5
T11 = MGm6
T12 = SGm6
T13 = MNPK (60-30-30 kg N/ha)
T14 = SNPK (64-30-30 kg N/ha)
T15 = MCtr
T16 = SCtr
The selected green manure crops will be sown in their recommended
spacings. The treatments will be laid out in a Randomized Complete Block Design
(RCBD) in factorial arrangement and will be replicated three times giving a
total of 48 plots in each location. Each plot will be 5 m x 4 m with 0.5 m and
1.0 m passages between plots and blocks respectively. (see figures).
1.0 m |
M Gm5 |
S Gm1 |
P14 |
P10 |
P6 |
P2 |
M NPK |
S Gm1 |
S Gm5 |
M Gm5 |
S Gm2 |
M NPK |
S NPK |
M Gm2 |
M Gm4 |
M Gm3 |
M Gm1 |
M Ctr |
0.5 m |
S Gm2 |
S Gm5 |
S Gm6 |
M Gm5 |
M Gm6 |
S Gm6 |
S Ctr |
S Gm4 |
M Gm1 |
P4 |
P8 |
P12 |
P16 |
S Ctr |
Fig.
1.a): The field layout in Damboa
Key to treatments
Ctr - Control
Gm - Green manure
M - Millet
S - Sorghum
REP I REP II REP
III
S Gm1 |
S Ctr |
M Ctr |
S Gm3 |
S Gm6 |
Fig.
1.b): The field layout in Maiduguri
Key to treatments
Ctr - Control
Gm - Green manure
M - Millet
S - Sorghum
3.2.2 Cultural Practices
The experimental sites will be cleared of debris, ploughed
and harrowed to fine tilth. Fourty eight plots will be laid out at each
location. Each plot will be 5 m x 4 m with Passage of 0.5 m between plots and 1.0
m between blocks. Seeds of the green manure crops will be scarified by soaking
in boiled water for a minute and dried before sowing. The seeds will be sown as
soon as rains are established, at the rates of 3 per hole and later thinned
down to two plants per hill. Seeds of early maturing varieties of millet (SOSAT)
and sorghum (ICSV III) will be treated with Apron Star 42 WS and planted 2
weeks after those of green manure crops, at the rates of five per stand in
spacings of 75 cm x 50 cm and 75 cm x 45 cm, respectively. Seedlings will be
thinned to two plants per hill two weeks after emergence. Weeding will be done
with hand hoe.
The NPK fertilizer will be applied at the rates of
60-30-30 for millet and 64-30-30 for sorghum, in split dose. The first dose of
30-30-30 will be applied at 2 weeks after sowing using NPK (20-10-10). At 6
weeks after sowing, the green manure crops will be harvested, weighed and then
incorporated in to the soil (in situ). The second dose of 30 Kg N/ha for millet
and 34 Kg/ha for sorghum, using Urea (46% N) will be applied on the same day
with the green manure incorporation.
3.3 Data Collection
3.3.1 Soil Sampling and Preparation
Prior to land preparation, fifteen soil samples will be
collected from different locations (randomly) across the each experimental site
at the depth of 0-15 cm. The samples will be bulked and mixed thoroughly to
form a composite sample. A sub-sample will be taken, air dried, crushed, sieved
through 2 mm sieve and kept in a polythene bag for physico-chemical analysis.
Post-harvest soil samples will be collected randomly in each plot, prepared and
kept separately for analysis.
3.3.2 Laboratory Analysis
3.3.2.1 Particle size
Particle size would be determined by Bouyoucos hydrometer
method as described by Udo et al.,
(2009). Forty grams of soil will be weighed into a glass cylinder and 200 ml of
distilled water and 50 ml of Calgon (Sodium hexametaphosphate) will be added.
The content will be allowed to stand overnight, after which it will be stirred
for 10 minutes. The suspension will then be transferred to a 1 litre cylinder
and filled to the lower mark with distilled water. The suspension will be
allowed to equilibrate with room temperature and the temperature will be
recorded. The suspension will be thoroughly stirred and time noted.
At 20 seconds the hydrometer will be inserted and reading
will be taken at 40 seconds for silt + clay. Temperature will also be noted.
The suspension will be re-shaken and reading taken at the end of 2 hours for
clay.
% material in suspension =
R = hydrometer
reading for soil. S = weight of soil
Rl =
hydrometer reading for blank. r = temperature
3.3.2.2 Soil reaction (pH)
The soil pH will be measured in 1:2.5 soil/water ratio
(Udo et al; 2009). Twenty grams of air-dry soil will be weighed in a 50 mls
beaker and 20 mls distilled water added to it. The mixture will be stirred with
glass rod and allowed to stand for 30 minutes. The pH would be measured with
glass electrode.
3.3.2.3 Electrical Conductivity (EC)
The EC would be determined in 1:2:5 soil-water suspension
(Rhodes, 1982). Ten grams of air-dry soil will be weighed in a 50 mls beaker
and 25 mls of distilled water will be added to it. The mixture will be stirred
with glass rod and EC will be measured with EC meter (Crision Conductivity).
3.3.2.4 Organic Carbon (OC)
The OC will be determined by Walkey and Black-wet
oxidation method (Udo et al., 2009).
Two grams of soil sample will be weighed and transferred to 250 ml flask. Ten millilitre
of 1N K2 Cr2 O7 solution will be added to it
and swirled gently to disperse the soil. Using an automatic pipette, 20 ml
concentrated H2SO4 will be added to the suspension and
allowed to stand for 30 minutes. After cooling, 100 ml of distilled water will
be added and then allowed to stand for 30 minutes. Few (3-4) drops of diphenylamine
indicator will be added and then titrated with 0.5 N FeSO4 to dark
green end point. Blank titration will be made in the same manner, but without
soil.
%OC =
Where:
% OC = Percentage organic carbon in soil sample
% organic matter in soil = %OC x 1.729
N
= Normality of FeSO4
V1 = ml of FeSO4 required for the blank
V2 = ml of FeSO4 required for the soil
sample
W =
weight of soil in gram
f
=
Correction factor 1.33
3.3.2.5 Total
nitrogen
Total nitrogen will be determined by macro-kjeldahl digestion
method described by Bremner and Mulvaney, (1987). One gram of soil will be
weighed into 500 ml macro-Kjeldahl flask and 1 tablet of Hg catalyst will be
added, followed by 10 ml of concentrated H2SO4. The
content will be heated for 3-5 hours until it becomes clear white solution.
After cooling, one hundred millimetre of distilled water will be added and
transferred into another clear macro-Kjeldahl flask. Fifty millilitre of H3
BO3 indicator solution will be put into 250 ml conical flask, which will be placed
under condenser of the distillation apparatus. The macro-Kjeldahl flask
containing the digest will then be attached to the distillation apparatus and
100 ml of 10 M NaOH solution will be poured into the macro-kjeldahl flask. The
distillation apparatus will be switched-on, until about 150 ml of the
distillate is collected. The distillate will be titrated with 0.1 N HCL to pink
end-point. The %N in the soil will be calculated using the following formular:
% N
=
Where,
a = ml of 0.1 N HCL
used to titrate the soil
b
= ml of 0.1 N HCL used to titrate the
blank
0.0014 = conversion factor
V1 = total volume of digest
V2 = ml of aliquot used for analysis
W =
weighed of soil (grains).
3.3.2.6 Available phosphorus (Bray - 1P)
Available
phosphorus will be determined by Bray and Kurtz (Bray – 1) method as described
by Olsen and Sommers, (1982). Two grams of soil will be weighed into 250 ml
plastic bottle and 14 ml of Ammonium fluoride (0.03N NH4F) in 0.025
N HCL (extracting solution) will be added and shaken on a mechanical shaker for
an hour. The content will be filtered through a No.1 white paper, and 20 ml of
the extract will be mixed with 5 ml of Ammonium molybdate in a test tube.
Finally, 1 ml of stannous chloride (SnCl2) will be added. After 5
minutes, colour will develop, and the percentage transmittance will be measured
on the spectrophotometer at wavelength of 660 nm. A standard curve will be
prepared and the P concentration in the soil sample will be extrapolated from
the standard curve.
3.3.2.7 Exchangeable bases
Ten
grams of the soil will be weighed into a 500 ml conical flask and 30 ml of 1N
NH4OAC will be added. The content will be shaken and then filtered
into 100 ml conical flask using No.1 filter paper. The volume will be made up
to 100 ml mark with 1N NH4OAC. The content will be analysed as
follows: for Ca and Mg; 20 ml of the extract will be pipetted into a 250 ml
conical flask and 100 ml of distilled water will be added, fifteen millilitre
of NH4 buffer, 10 drops each of KCN, TEA, NH2 O4HCL
and EBT indicator will be added and titrated with 0.02 N Na2 EDTA to
bluish end point. For Ca alone, the above procedure will be followed except that
EBT will be replaced by Mureoxide indicator and NH4 buffer will be
replaced with 20% NaOH. The content will be titrated with 0.02 N Na2
EDTA o a reddish end point; Potassium and Sodium will be determined by flame
photometer (Rhoades, 1982).
3.3.2.8
Exchangeable acidity
Exchangeable H+ and Al3+ will be
extracted with 1 N KCL and the extract will be titrated with 0.05 N NaOH. The
total acidity will be obtained by summing up the amounts of H+ and
Al3+ obtained, (Grant, 1982).
3.3.2.9 Effective cation exchange capacity (ECEC)
The ECEC of the soil sample will be computed by
summation of exchangeable bases and exchangeable acidity
(Ca2+
+ Mg2+ + K+ + Na+ + H+ + Al3+).
3.3.3 Plant Sample Collection
Samples of the green manure will be taken at the time of
incorporation. They will be oven-dried at 650C and kept for
analysis. At harvest, five plants will be selected randomly from each plot and
their height and panicle length will be measured. Their leaves, grains and
straws will be sampled for N, P and K analysis. Crops in the net plots area of
3 m x 2.5 m (7.5 m2) will be harvested, and grain yield, straw yield
and 1000 seeds weight will be measured.
Plants height (cm) will be measured from the ground level
to the tip of the panicle with a meter rule. The mean of 5 plants will be
recorded.
Panicle length (cm) will be measured with a meter rule and
the mean for 5 plants in each plot will be recorded.
Leaves, straws,
grains and green manure samples will be oven-dried at 650C, and
finely ground using a pistle and mortar. The samples will then be kept
separately in air-tight polythene bags for N, P and K content analysis.
Grain
yield (Kg/ha) will be obtained by harvesting all plants from the net plots area
of 3 m x 2.5 m (7.5 m2), air-dried, threshed, cleaned and weighed.
One
thousand seed weight (g) will be obtained by counting and weighing 1000 seeds
from each seed stock taken from each plot.
Straw
yield (kg/ha) will be obtained by harvesting all the straws in each net plot,
air-dried and weighed.
3.3.4 Plant Analysis
Plant samples will be analysed using single acid
digestion method for different mineral elements (N, P, K, Ca, and Mg). Two
hundred milligram (200 mg) of the plant material will be weighed into a clean
100 ml Kjeldahl flask and 5 ml of concentrated H2SO4 will
be added. The flask will be swirled gently and then heated for 40 minutes. One
millilitre (1 ml) of 4% V/V solution of 62% HClO4 in concentrated H2
SO4 will be added and heated for 10 minutes to obtain a clear
digest. The digest will be cooled and transferred to a 50 ml volumetric flask
and diluted with distilled water to mark. A blank will also be prepared.
3.3.4.1 Determination of Nitrogen
Nitrogen will be analysed by Kjeldahl distillation and
titration procedure. Ten millilitre (10 ml) aliquot of digest will be mixed
with 10 ml of 4% NaOH and distilled into boric acid-indicator solution. When
the distillate reaches 35 ml mark, the flask will be removed and then titrated
with 0.01N H2 SO4 to pink colour end points.
3.3.4.2 Determination of P (Vanado-molydate method)
Two millilitres of the plant digest will be pipetted out
and transferred into 25 ml volumetric flask. Five millilitres of
vanodo-molybdate reagent will be added and then diluted to mark. The content in
the flask will be allowed to stand for 10 minutes for colour development before
taking P reading on a spectro-photometer at 400 nm. A graph of percentage
absorbance against ppm P concentration will be plotted using P standards (0 to 0.5 µgml-1).
Phosphorus concentration in the plant sample will be extrapolated from the
graph.
3.3.4.3 Determination of Potassium
A series of standard solution containing 0 – 5 µgml-1
of K and 2.5 ml of blank digest per 500 ml standard will be prepared. A
standard curve will be made and K content of sample will be determined in flame
photometer and K concentration extrapolated.
The uptake of nitrogen, phosphorus and potassium by millet
and sorghum plants will be computed using the formula given below:
Nutrient uptake (Kg ha-1)
=
x Dry weight (Kg ha-1)
3.4.1 Cost-benefit
Analysis
The cost-benefit ratio for using green manure and NPK
fertilizer in millet and sorghum production will be analysed as described by Powon
et al., (2009) in order to ascertain
the benefit in monetary terms of each treatment.
CBR
=
GI – VC
VC
Where: CBR =
Cost-Benefit Ratio
GI = Gross
Income
VC =
Variable Cost
GI-VC = Net
benefit (NB).
The
project is considered viable if and only if the CBR is greater than one (Miller, 2001).
3.5 Statistical
Analysis
Data collected from the field and laboratory will be subjected
to analysis of variance (ANOVA). Duncan Multiple Range Test (DMRT) will be used
to separate the means that are significantly different at (P<0.05). All statistical
analysis will be performed with Computer Software STATISTIX (Sx) Version 17.0.
Analytical Software (Statistix 2010).
3.6 Expected Outcome
The study is expected to provide information on the
effects of various green manure crop species on yields of millet and sorghum
and soil fertility status. Cost-Benefit ratio will also be known. The crops
productivity, soil fertility and economic benefit of using green manure will be
improved. The most promising green manure species will be identified that will
be useful for sustainable crop production in Borno State.
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