Influence of Organic Manure on Phosphorus and Potassium Fractions in Soil Planted with Soybean

Field experiments were carried out on the Research Farm of the Federal University of Agriculture Abeokuta, (FUNAAB), Ogun State, Nigeria to determine the effects of poultry manure (PM) on soil P and K fractions and nutrient availability to soybean plants. Treatments consisted of five rates of PM (0, 2.5, 5.0, 7.5 and 10 tha-1) and 100 kg ha-1 of NPK 20:10:10 fertilizer as basal application. Soybean (TGx 1448-2E) was cultivated in two planting seasons. The experimental design was randomized complete block design with three replicates. During the second year (second season), treatments were not applied to evaluate residual effects. Results from phosphorus fractionation showed that residual P, redundant soluble P and occluded P had highest values of the inorganic P in the first planting season. Application of PM reduced P fixation, residual P and occluded P fractions in the soil in the second season. Available P significantly (P ≤ 0.05) increased in most treated soils and greater in second season. The values of total and mineral K were higher than those of the other forms. The abundance of soil K fractions in the soils followed the order: Total K > mineral K > non exchangeable K > 1N HCl K > 1N HNO3 K > available K > exchangeable K > water soluble K. There were increases in all the K fractions. Application of PM significantly increased concentrations of N, P and K in plant tissue. The study concluded that application of 10 tha-1 PM minimised P fixation, increased available K, increased nutrient uptake and improved crop yield in soybean. Therefore, poultry manure is recommended for production of soybean in Abeokuta soil.