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

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.