Effects of rate of phosphorus fertilizer on crop growth and yield in rice-soybean intercropping system

The study was aimed at investigating the effects of rate of phosphorus fertilizer on growth and yield in rice-soybean intercropping system. Phosphorus fertilizer was applied at the rate of 0, 45, 60 and 75 kg P ha-1 while the three cropping patterns were sole rice, sole soybean and rice + soybean intercrop. Phosphorus and cropping patterns were combined in a 4 x 3 factorial and laid out in a randomized complete block design with three replicates. Results showed that increasing rate of P fertilizer significantly (P<0.05) increased growth parameters in both rice and cowpea. All components of yield of soybean were found to show significant (P<0.05) phosphorus and cropping pattern interactions. Application of P at 45, 60 and 75 kg ha-1 enhanced rice yield by 23%, 57.4% and 88.3% respectively, while soybean yield was increased by 28.5%, 65.7% and 73.5% at same respective P fertilizer rates. Interactive effects of phosphorus and cropping pattern for yield of both rice and cowpea were found to be significant (P<0.05). LER increased with P rate ranging from 42% to 71%. SPI showed a linear trend with P fertilizer rate. Agronomic efficiency of P fertilizer was generally higher in the cereal crop (rice) relative to the legume (soybean) at all levels of application. The results of this study have shown that to achieve a positive interspecific competition between rice and soybean in the rice-soybean intercropping system it is more appropriate to apply phosphorus 60 kg P ha-1.