# Straw return combined with single-season phosphorus application for rapeseed enhances the annual productivity and phosphorus use efficiency under rapeseed–rice rotation

## TL;DR

Returning straw and applying phosphorus only during the rapeseed season improves productivity and phosphorus use in a rapeseed-rice rotation system.

## Contribution

This study reveals the synergistic benefits of straw return and single-season phosphorus application in enhancing productivity and phosphorus use efficiency.

## Key findings

- Straw return increased annual yield and phosphorus use efficiency by 22.28% and 19.4%, respectively.
- Single-season phosphorus application (P3) improved phosphorus uptake and utilization by 92.51% compared to full-season application.
- Straw return combined with P3 increased soil organic matter and P-soluble bacteria abundance.

## Abstract

The rapeseed–rice rotation system involves high phosphorus application rates in both seasons, with low phosphorus use efficiency and a large amount of straw produced. However, the synergistic mechanism of phosphorus fertilizer management and straw return in this system remains unclear.

A two-factor split-plot experiment was designed to systematically investigate the effects of straw incorporation and seasonal phosphorus (P) reduction on annual productivity, P-use efficiency, soil fertility, and microbial community structure in a rapeseed-rice rotation system in 2022-2024. The main plot was no straw return (S1) and straw return (S2) for both the rapeseed and rice seasons. The subplot was set with three P application modes: no P application throughout the year (P1), P application throughout the year (P2), and P application only during the rapeseed season (P3) .

S2 significantly enhanced annual yield and P-use efficiency of the rapeseed-rice rotation system, with the best results observed under treatment P3. Under treatment S2, the P fertilizer uptake and utilization rate increased by 22.28%, the partial factor productivity of P fertilizer improved by 19.4%, and the agronomic efficiency of P fertilizer increased by 67.52% compared to that under treatment S1. The P3 treatment further improved P-use efficiency, with the P fertilizer uptake and utilization rate being 92.51% higher than that of the P2 treatment. Additionally, the S2P3 treatment significantly increased rice root morphology and ATPase activity, soil organic matter content, the total P contents and the relative abundance of soil P-soluble bacteria in the soil.

Straw return combined with rapeseed single-season P application significantly increased the annual productivity of the rapeseed-rice rotation system, improved the ATPase of rice, and increased the total P and Olsen-P contents in the soil through straw decomposition and the activity of soil P-soluble bacteria. This significantly improved P-uptake efficiency, achieved P reduction and increased P-use efficiency.