Effect of rhizobium inoculation on rhizosphere phosphorous dynamics and fertilised phosphorous use efficiency in a maize–pigeon pea intercropping system in weathered tropical soil

Abstract

Introduction: Low phosphorus (P) use efficiency (PUE) of fertiliser is a critical problem in sustainable crop production, especially in strongly weathered tropical soils with a high P-fixation capacity. Both intercropping and rhizobium inoculation have shown to improve the P availability of rhizosphere soil, but the effect of a combined approach of using both intercropping and rhizobium inoculation is still unclear. In this study, we aimed to evaluate the effect of rhizobium inoculation on the soil–plant P dynamics and fertilised PUE under the intercropping system in strongly weathered tropical soil. Materials and Methods: We conducted an 85-day cultivation pot experiment with pigeon pea (PP) and maize using highly weathered tropical soil under eight treatments: monocropping (CS) or intercropping, with or without rhizobium (Bradyrhizobium elkanii USDA61) inoculation (−I, +I) and with or without P fertilisation (0P, 50P) (2 × 2 × 2 = 8 treatments). We evaluated the effects of intercropping and rhizobium inoculation on plant growth parameters, P dynamics of the rhizosphere and bulk soil using the Hedley P fractionation method, the amount of organic acid from plant roots as a plant P-mobilising capacity, and fertilised PUE. Results: Total plant P uptake per pot was significantly increased by intercropping but not by combining intercropping and rhizobium inoculation, resulting in better fertilised PUE only in intercropping. The available inorganic P (Pi) and less labile Pi of the soil were higher in the rhizosphere than those in the bulk by intercropping under 50P and were similar in PP + I under 50 P. The amount of organic acid per pot under 50P increased with each treatment, that is, intercropping and rhizobium inoculation, but not with their combination. Conclusion: The intercropping system has a strong potential to improve PUE by stimulating the P-mobilising capacity of intercropping plant roots, whereas rhizobium inoculation of the intercropping system did not improve PUE in this study.