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Effect of Inoculating Bradyrhizobium on Phosphorus Use Efficiency and Nutrient Uptake of Soybean Intercropped with Sugarcane in Calcareous Soil of Metahara, Central Rift Valley, Ethiopia

Tesfaye Fituma, Tamado Tana and Anteneh Argaw

At a soil pH value of above 7.0, inorganic phosphorus (P) is highly susceptible to precipitation as insoluble form that is unavailable to the plants. Hence, a field experiment was conducted at Metahara Sugar Estate under irrigation during the 2014/15 cropping season to evaluate the effect of inoculating Bradyrhizobium on P uptake and P use efficiency of soybean intercropped with sugarcane. The treatments consisted of three levels of inoculation (Legumefix, SB6B1 and uninoculated) and four rates of P (0, 23, 46 and 69 kg P₂O₅ ha^-1). The experiment was laid out as a randomized complete block design (RCBD) in a factorial arrangement and replicated three times. Analysis of the data indicated that Bradyrhizobium inoculation significantly increased plant N concentration and P uptake compared to the uninoculated treatment. But the effect of P rates and its interaction with inoculation was not significant on N concentration and P uptake but significantly increased total P uptake at the application of 69 kg P₂O₅ ha^-1. P use efficiency indices were improved in response to inoculating the crop with Bradyrhizobium. The higher AE (13.6 kg kg^-1), PRE (31.8%) and PUE (10.6 kg kg^-1) were obtained by SB6B1 inoculation and higher PE (117.2 kg kg^-1) and APE (161.7 kg kg^-1) were obtained by Legumefix inoculation all at 23 kg P₂O₅ ha^-1 except PE which recorded at 69 kg P₂O₅ ha^-1. Thus, it can be concluded that SB6B1 isolate will be used as the best inoculant followed by Legumefix isolate with 23 kg P₂O₅ ha^-1 of P fertilizer rate. However, strategies for increasing P use efficiency by adopting best management practices like co-inoculation of phosphate solubilizing microorganism or mycorrhiza with these Bradyrhizobium inoculants should be adopted to enhance P use efficiencies.