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 PROBLEMIn 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:determine the NPK content in 15 green manure crop species;identify the best six green manure crops species to be used in sorghum and millet production; investigate the effects of the selected species on the growth, yields and nutrient uptake by the sorghum and millet; investigate the effects of the selected green manure crop species on the soil chemical properties, and 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: -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.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.Determine desired services from green manure:N supply for subsequent cropReduce soil erosionBuild soil organic matter.Reduce leaching losses of residual N from previous crop.Provide seed, forage, or other economic product.Pest, disease or weed suppression.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.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?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 METHODS3.1 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;Crotalaria junceaCentrosema pubescensStylocanthes guianeensisCalopogonium mucunoidesPeuraria phaseoloidesMucuna pruriensSesbania rostrata Sesbania sesbanCanavalia ensiformisTrifolium incanatumAesehynonene histrixMucuna rajadaChamaecrista refundifoliaCarjanus cajan Dolichos lablabTop 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 = SGm4T9 = MGm5T10 = SGm5T11 = MGm6T12 = SGm6T13 = 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). REP I REP II REP III 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 Fig. 1.b): The field layout in Maiduguri Key to treatments Ctr - Control Gm - Green manure M - Millet S - Sorghum3.2.2 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 Collection3.3.1 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 Analysis3.3.2.1 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 = temperature3.3.2.2 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 1.333.3.2.5 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 factorV1 = total volume of digestV2 = ml of aliquot used for analysisW = 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. 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