Rhizobium inoculation reduces P and K fertilization requirement in corn-soybean intercropping

The field experiment was carried out at Tanzania Coffee Research Institute (TaCRI) for two consecutive years to assess the effects of Rhizobium inoculation, supplemented with phosphorus and potassium on nutrient uptake in soybean intercropped with maize. The experiment was laid out in split-split plot design with 2x4x7 factorial arrangement replicated thrice. The main plots had two rhizobial inoculation treatments, while the sub plots were comprised of four cropping systems: Maize (sole-crop), Soybean (sole-crop) and two intercropping at different soybean spacing (75 x 20 and 75 x 40 cm). The sub-subplots were assigned to fertilizer levels (kg ha(-1)): control; 20K; 40K; 26P; 52P; 26P + 20K; 52P + 40K. The statistical analysis was performed using ANOVA. The fisher's L.S.D. was used to compare treatment means at p=0.05 level of significance. The results indicated that soybean pure-stand significantly improved the uptake of Mg over the soybean under intercropping systems for the two cropping seasons. The uptake of Fe increased in intercropped soybean for the first cropping season relative to soybean pure stand. Rhizobium inoculation significantly improved the uptake of all other macro nutrients (N, K, P, and Mg) and micronutrients (Fe, Cu, Zn, Mn) in soybean shoots over un-inoculated soybean. Fertilization of soybean with P and K significantly increased the uptake of N, P and K for both cropping seasons. However, the uptake of macro nutrients such as calcium (Ca) and Magnesium (Mg) and micro nutrients such as Fe and Cu decreased with the increase of P and K fertilizers. P and K fertilization did not significantly affect the uptake of Mg and Mn for the two cropping seasons. Based on the findings of this study, Rhizobium inoculation and P and K fertilization at lower rates are recommended for improved uptake of macro and micro nutrients in legumes such as soybean.