Moderate phosphorus reduction under split drip fertigation maintains maize yield and coincides with closer root–available phosphorus spatial correspondence

Introduction Phosphorus (P) has low mobility in soil, so crop P acquisition depends on both P availability and its spatial accessibility to roots. We hypothesized that moderate P reduction under split fertigation could maintain maize productivity by improving the coordination between available P and root distribution. Methods A two-year field experiment was conducted in irrigated spring maize in Inner Mongolia, China. Split monoammonium phosphate fertigation was applied at 105 (CP1), 127.5 (CP2), and 150 kg P 2 O 5 ha -1 (CP3), together with a no-P treatment (CP0) and conventional basal diammonium phosphate application at 150 kg P 2 O 5 ha -1 (CK). Root length density and Olsen P were measured in paired soil blocks within the 0–40 cm soil profile at silking, together with plant P accumulation, biomass, grain yield, and P-use efficiency. Results CP2 increased Olsen P availability and root proliferation in the middle and deeper soil layers and showed closer spatial correspondence between root length density and Olsen P at 20–40 cm. These changes were associated with greater post-silking P accumulation and biomass. Reducing P input by 15% maintained grain yield at the level of CP3 and increased yield by 4.07% relative to CK, while apparent P recovery efficiency and P agronomic efficiency increased by 77.36% and 54.62%, respectively. Further reducing P input to 105 kg P 2 O 5 ha⁻¹ decreased P accumulation, biomass, and yield, whereas 150 kg P 2 O 5 ha -1 provided no additional yield benefit. Discussion Under the conditions of this study, moderate P reduction under split fertigation maintained maize yield while reducing fertilizer input and enhancing P-use efficiency, and this response was associated with closer spatial correspondence between root distribution and soil available P.