Effect of inoculating Bradyrhizobium on phosphorus use efficiency and nutrient uptake of soybean in calcareous soil, central Rift Valley, Ethiopia
At a soil pH value of above 7.0, inorganic phosphorus (P) is highly susceptible to precipitation as insoluble form that is unavailable to plants. Hence, a field experiment was conducted at Metehara 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 (Legume fix, SB6B1 and uninoculated) and four rates of P (0, 10, 20 and 30 kg Pha-1). The experiment was laid out in 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. 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 30 kg Pha-1. Phosphorus use efficiency indices were improved in response to inoculating the crop with Bradyrhizobium. The highest AE (13.6 kg kg-1), PRE (31.8%) and PUE (10.6 kg kg-1) were obtained by SB6B1 inoculation and the highest PE (117.2 kg kg-1) and APE (161.7 kg kg-1) were obtained by Legumefix inoculation all at 10 kg P ha-1except PE which recorded the highest at 30 kg P ha-1.Thus, it can be concluded that SB6B1 isolate can be used as the best inoculant followed by Legumefix isolate with 10 kg P ha-1of P fertilizer. 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.