Effects of NPK and poultry manure rates on the growth, nitrogen fixation and grain yield of soybean (Glycine max (l) Merrill).

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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 semideciduous 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) on grain yield apparently because of increased nodulation and N fixation. Generally, there were increase in nodulation and nodule effectiveness observed in poultry manure (2 tons/ha) treatments. Further studies v can be executed to verify the results, but such must be sited where irrigation can be done when rainfall fails.
Thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture of the College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfillment of the requirements for the award of Master of Philosophy Degree in Agronomy (Crop Physiology), 2016.