Response of Soybean [Glycine max (L.) Merrill] to Sources and Levels of Phosphorus

A field experiment was conducted during rainy seasons of 2007-2009 in India (Manipur) to study the effect of different sources and levels of phosphorus on productivity of soybean [Glycine max (L.) Merrill]. The treatments consisted of four sources of phosphorus [Single super phosphate (SSP), Di-ammonium phosphate (DAP), Single super phosphate (SSP)+Phosphate solubilizing bacteria (PSB), Di-ammonium phosphate (DAP)+Phosphate solubilizing bacteria (PSB)], four levels of phosphorus (20, 40, 60 and 80 kg P2O5 ha) and one absolute control(without any fertilizer and PSB). Application of SSP+PSB produced significantly higher number of nodules per plant, dry weight of nodules per plant, number of pods per plant and 100-seed weight than the other treatments. Maximum grain yield and total phosphorus uptake were also recorded when using SSP+PSB. Yield www.ccsenet.org/jas Journal of Agricultural Science Vol. 4, No. 6; 2012 45 attributing characters, grain and stover yield were increased with increasing levels of phosphorus. Regarding evaluation of various efficiency fractions of soybean, agronomic efficiency, physiological efficiency and phosphorus use efficiency had more pronounced effects on combined application of SSP+PSB. However, apparent recovery of phosphorus was higher in DAP+PSB due to higher stover yield and higher phosphorus uptake. Among the different levels the efficiency fractions increase up to 60 kg P2O5 ha and declined at 80 kg P2O5 ha.