Abstract

Field trials were conducted during the rainy seasons of 2009, 2010 and 2011 in Samaru in the northern Guinea Savanna zone of Nigeria to evaluate the response of soybean to separate and combined applications of farmyard manure (FYM) and mineral phosphorus fertilizers levels. Soybean varieties TGx 1448-2E and TGx 1019-2E were grown with three levels of FYM (0, 1 and 2 t/ha) and four levels of P (0, 13.2, 26.4 and 39.6 kg P/ha) in all possible factorial combinations laid out as a randomised complete block design, replicated four times. Leaf area index, number of days to 50% bloom stage nodule dry weight per plant, number and weight of pods per plant and 100-seed weight were similar for both varieties. TGx 1448-2E was shorter but produced more total dry matter (TDM) than TGx 1019-2E. Although TGx 1448-2E produced higher grain yield than TGx 1019-2E, the difference was not significant. Application of FYM increased plant height nodule dry weight, TDM, 100-seed weight and grain yield per hectare. Application of 1 t/ha of FYM increased grain yield by 16.7% compared with plots without FYM but there was no difference by increasing FYM to 2 t/ha. Phosphorus application increased grain yield significantly and application of 26.4 kg P/ha increased grain yield by 46.6% and 16.0% compared with plots without P and with 13.2 kg P/ha respectively when averaged over the three years. There were no interactions between FYM and inorganic P on grain yield in any of the years. The result showed that both varieties were similar in grain yield and 1 t/ha of FYM or 26.4 kg P/ha produced similar grain yields above 2 t/ha. Regression equation across the years showed soybean responded optimally to P rates ranging from 15.9 to 39.7 kg P/ha for grain yields of 1950.2 to 2665.4 kg/ha depending on the fertility status of the soil.

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