Abstract

A soil culture experiment was carried out in the greenhouse at Obafemi Awolowo University, Nigeria, to assess the effects of organo-mineral fertilizers consisting of water hyacinth compost at the rates of 0, 2.5 and 5 t/ha compounded with and without N (0 and 25 kg/ha urea) and P (0 and 26 kg/ha single superphosphate - SSP) on soil chemical properties, growth and yield of soybeans planted on Itagunmodi soil series (an ultisol). Two experiments were set up simultaneously. One set of plants was allowed to grow for 8 weeks and terminated at 50% flowering while the other was allowed to pod. The experiments were repeated to assess the residual effects of the treatments. In the first experiment, 5.0 t/ha water hyacinth compost + N and P (WC2F) significantly (p<0.05) improved plant height (PLHT) and shoot dry weight (SDW). Also, WC2F and in most cases, followed by WC2 (5.0 t/ha water hyacinth) had significant (p<0.05) residual effects on PLHT, NOLP (number of leaves per plant), SDW and RDW (root dry weight). The mean soil pH and available P for the two plantings were significantly (p<0.05) higher in both WC2 and WC2F than in the control. The mean exchangeable cations (Na, Ca and Mg) were also significantly higher in WC2 than the control. In the second experiment, CW2F followed by WC2 produced the highest pod and grain weights per plant (PWPP and GWPP). The lowest values for these parameters were obtained in the control. Similarly, WC2F and WC2, unlike the control and N and P only (F), had significant residual effects on the NOPP (number of pod per plant), PWPP and GWPP. It was concluded that WCF2 and WC2 were the best in enhancing both the growth and yield parameters of soybean. Hence, water hyacinth composted with N and P was a better source of nutrients for soybean production than their individual applications.

Key words: organomineral fertilzers, ultisol, water hyacinth compost, soybean.