Influence of Rhizobia Inoculation and supplementation with phosphorus and potassium in soybean-maize intercropping system

Abstract

A field experiment was carried out at Tanzania Coffee Research Institute (TaCRI) farm, for two consecutive years (2015 and 2016). The objective of this study was to assess the effects of cropping systems, Rhizobium inoculation and fertilization with P and K on farm productivity of both soybean and maize. The experiment was laid out in split-split plot design with 2 x 4 x 7 factorial arrangements and replicated thrice. The main plots comprised two rhizobia inoculation treatments, while the sub plots were comprised of: Maize pure stand (75 x 60 cm); Soybean pure stand (75 x 40 cm); maize-soybean intercropping (75 x 60 cm and 75 x 20 cm), maize and soybean respectively; and the last cropping system was maize-soybean intercropped (75 x 60 cm and 75 x 40 cm), maize and soybean respectively. The sub-subplots were assigned the following fertilizer levels (kg ha-1 ): control (0 kg ha-1 ); 20 K; 40 K; 26 P; 52 P; 26 P + 20 K; 52 P + 40 K. The 3-way analysis of variance (ANOVA) in factorial arrangement was performed. The STATISTICA software program was used. The fisher’s least significance difference (L.S.D.) was used to compare treatment means at p = 0.05 level of significance. The results indicated that rhizobia inoculation and fertilization of crops with P and K significantly improved mineral composition in the rhizosphere soil of soybean; nutrient uptake in soybean shoots; nitrogen fixation and chlorophyll concentration in soybean. Furthermore, rhizobia inoculation and P and K fertilization significantly improved plant growth and final yield of both soybean and maize. Cropping systems were also assessed and found that intercropping was advantageous since the values of land equivalent ratios (LER) were greater than one. In general, several parameters tested in this study have shown to perform better in combined lower rates (20 kg K ha-1 +26 kg P ha-1 ) of P and K. It is therefore recommended that the combined lower rates of these fertilizers should be adopted and be used by farmers in areas with similar characteristics as that of study area.