Soybean is a legume and has a great potential to fix atmospheric nitrogen and improve soil fertility in addition to providing edible grains. Nitrogen fixation, however, is constrained by environmental factors which include soil nutrient inadequacy. A field experiment was carried out at Nkorang, Nkawie, which fall under the moist semi-deciduous forest vegetation zone in Ghana, to investigate the effects of different rates of NPK and poultry manure on growth, N fixation and grain yield of soybean under zero tillage cultivation.The experimental design used was a 3x3 factorial arranged in a randomized complete block design. The factors studied were poultry manure rates and NPK rates. NPK rates were 0, 45 and 90 kg/ha and poultry manure rates were 0, 2, and 4 tons/ha. Each treatment was replicated four times and there were nine plots per block.The field was slashed and glyphosate 360 (isopropylamine salt) was applied as a pre-plant herbicide at 2 L per hectare of water two weeks after slashing. Plots were then laid with each plot measuring 2.5 m x 4 m and planting was done at a spacing of 10cm x 5 cm. Data taken on plants included plant height, number of leaves, number of branches, crop growth rate, shoot biomass, leaf area, nodule number, number of effective nodules, number of pods per plant, number of seeds per pod, hundred seed weight, grain yield and amount of N fixed.The results of the experiment showed that application of NPK or poultry manure significantly affected the growth of soybean. Higher rates of NPK and poultry manure caused significantly higher growth in some parameters.Generally, yield components were not affected by NPK or poultry manure rates. This observation was mainly due to low rainfall at the onset of pod formation. In contrast, poultry manure rate at 2 tons/ha had a significanteffect (p<0 .05="" a="" and="" apparently="" because="" effectiveness="" fixation.="" further="" generally="" grain="" ha="" in="" increase="" increased="" manure="" n="" name="page8" nodulation="" nodule="" observed="" of="" on="" poultry="" studies="" there="" tons="" treatments.="" were="" yield="">
can be executed to verify the results, but such must be sited where irrigation can be done when rainfall fails.

Soybean [Glycine max (L.)Merrill] is an annual legume that belongs to the family Leguminosae and subfamily Papilionoidae (Berk, 1992).It produces pods on an erect stem and has opposite and ovate unifoliate primary leaves, alternate and trifoliolate secondary leaves and compound leaves with four or more leaflets occasionally present(SheafferandMoncada, 2012). It is a self pollinating diploid plant with 40 chromosomes (2n=40 chromosomes)(Chang andQiu, 2010).

In Ghana, average yield of soybeanis 1.5Mt/ha, however, achievable grain yield of soybean under rain-fed conditions is estimated at 2.5Mt/ha (40% more than average yield) (MOFA, 2011). According to Mbanya (2011), low yield of soybean in Ghana can be attributed to low level of adoption of technology such as soil fertility management strategies that would improve soybean production.

The poor soil fertility problem is well recognized as the main obstacle to maximizing crop yield (Hilhorst et al., 2000). Recent research works have brought to light some approaches to curb the poor soil fertility challenge which include the supply of organic and/or mineral nutrients to the soil. Nevertheless, the use of mineral fertilizers by smallholder farmers in sub-Saharan Africa is not properly adhered to owing to high costs, unavailability and at times lack of technical knowledge(Bationo et al., 2006). Adequate sources of organic fertilizers are also difficult to acquire as larger quantities are required as well as competitive alternative uses of organic sources; farmers prefer to give stovers to farm animals rather than use them as farm manure and consequently add nutrients to the soil. Again, organic fertilizers are also bulky and difficult to transport (Alimi et al., 2006).

The challenges arising out of the use of organic and inorganic fertilizers have led to exploration of other economical and environmentally friendly means of supplying nutrients to crops. One of suchmeans is biological nitrogen fixation. For a very long period, biological nitrogen fixation (BNF) in legumes has been a key constituent of many cropping systems throughout the world. Gregory (2006) stated thatglobal nitrogen

fixation in the soil before extensive human activity was 90-140 million ton N ha- 1. Soybean has the capacity to acquire its total Ndemands from symbiotic nitrogen fixation and leaves excess nitrogen reserves in the soil for subsequent crops (Salvagiotti et al., 2008). Biological nitrogen fixation (BNF), therefore is an inexpensive and environmentally friendly means of improving crop yield, reducing N application and enhancing the soil quality. BNF consequently reduces the dependence on mineral fertilizers that could be costly and unavailable to smallholder farmers.

Even though rhizobia seem to be widely distributed in the soil (Herridge et al., 2002), N fixation is closely linked to the physiological condition of the host plant. Crop stress factors such as, nutrient deficiency, insufficientassimilates and crop disease occurrence can impair the growth and development of the crop, and subsequently, adversely affect the symbiotic relation of plants and rhizobia. As a result, the rhizobia strain existing in the soil will not be able to successfully infect plant roots and consequently aid N fixation to their maximum potential (Zahran, 1999).Eventually, little biomass is produced and amount of N fixed is reduced. The ability of the plant to ameliorate the soil, as well as improve yield will consequently be greatly hampered.

Biological nitrogen fixation (BNF) is largely influenced by four main factors namely, the effectiveness of the symbiotic relationship between the host plant and the rhizobia strain, capacity of the plant to store N, the amount of N in the soil available to crops and environmental limitations (Van Kessel and Hartley, 2000). Soil as a medium through which crops grow and develop, therefore, has greater effect on N fixation, growth and yield of crops. Hence, the control of the soil environment plays a very prominent role in securing crop productivity. In soil management, recent research has indicated that supplying starter soil nutrient at early stages of crop vegetative growth can increase pod yield and crop biomass (Yinbo et al., 1997).

According to Omondi et al. (2014), cultivation of crops under no tillage system enhances biological nitrogen fixation and when it is practiced for a long period is able to improve most soil properties and consequently leads to yield increases. This is because no tillage contributes to increased soil fertility and soil organic carbon content, improved moisture conservation and other soil benefits.

It is therefore hypothesized that growing soybean under no tillage cultivation with the application of minimal NPK or poultry manure can enhance biological nitrogen fixation and produce yields equivalent to yields obtained by applying higher amount of mineral or organic fertilizers.

The general objective of the research was therefore to assess productivity of soybean by enhancing BNF through inorganic and organic fertilizer applications under no tillage cultivation.

The specific objectives were to:
determine the effects of NPK and poultry manure on growth and yield of soybean.
determine the effects of NPK and poultry manure on nodulation and N-fixation.

determine the combined effect of NPK and poultry manure on growth, N-fixation and yield of soybean.

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Item Type: Ghanaian Topic  |  Size: 62 pages  |  Chapters: 1-5
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