Soybean (Glycine max (L.) Merrill) intercropping with reduced nitrogen input influences rhizosphere phosphorus dynamics and phosphorus acquisition of sugarcane (Saccharum officinarum)

Abstract

Reducing nitrogen (N) input can improve crop productivity in cereal-legume intercrops, but the impact on phosphorus (P) acquisition is unclear. A 10-year (2009–2018) field experiment was conducted to quantify how P acquisition by sugarcane (Saccharum officinarum) was affected by intercropping with soybean (Glycine max (L.) Merrill at 1:1 and 1:2) with two N inputs (300 kg ha–¹ [reduced], 525 kg ha–¹ [conventional]). Nitrogen was supplied only to the sugarcane crop, and soybean received no N. There was a significantly higher land-equivalent ratio of sugarcane-soybean intercropping than of the sole cropping, and the intercropping advantage was more pronounced under reduced N input which can be associated with high degree of complementary N use. Furthermore, soybean intercropping with reduced N input stimulated acid phosphomonoesterase activity and depleted organic P in the rhizosphere of sugarcane, resulting in increased sugarcane stem P concentration and system P-use efficiency. The interspecific facilitation of P acquisition could be associated with the increased symbiotic N₂ fixation in soybean, soil microbial biomass and activity under reduced N input. In conclusion, soybean intercropping with reduced N input to sugarcane enhanced rhizosphere enzymatic organic P transformation and sugarcane P acquisition, which may contribute to maintaining a sustainable sugarcane production under low N supply. The findings advance our understanding of interactions between N and P cycling and provide new evidence for the value of cereal-legume intercrops in reducing fertilizer input.