Fertilization and inoculation as factors affecting growth, nodulation, seed yield and seed protein content of soybean (Glycine max (L.) Murrill) under lowland rice-based cropping system

The application of N,P, and K singly or in combination with or without inoculation significantly increased the yield over the control. The rate of 30-30-30 kg NPK/ha significantly increased soybean seed yield by 45.48% over the control plants. Nitrogen, phosphorus, and potassium had equal importance in improving soybean growth, increasing seed yield, as well as protein content. Inoculation alone significantly increased soybean seed yield by 43.78% over the control plants. Likewise, it yielded comparably with NPK singly or in combination with or without inoculation. Seed yield was positively and linearly correlated to the number of filled pods per plant (r=0.96) and seed protein content(r=0.69). The protein content of soybean, irrespective of variety was significantly increased with the application of NPK. Furthermore, inoculation alone improved the protein content of soybean. The addition of P and K alone or in combination markedly increased the protein content over the control. Seed protein content was linearly and positively related to number of effective nodules (r =90) and number of filled pods (r = 0.98). Furthermore, inoculation alone and NPK application either singly or in combination markedly improved plant height at maturity and number of filled pods over the control. Number of filled pods was linearly and positively related to plant height (r=0.70), length of roots (r=o.71), and seed protein content (r=0.98). UPL Sy-4 and BPI Sy -4 matured earlier (77 and 79 DAE, respectively) than SJ-2 (95 DAE ). Likewise, UPL Sy-4 and BPI Sy-4 were relatively shorter than SJ-2. Furthermore, SJ-2 variety yielded significantly higher than UPL Sy-4 but comparable with BPI Sy-4. On the other hand, BPI Sy-4 had significantly higher seed protein content than SJ-2 and UPL Sy-4, the latter two being comparable.