Effects of nitrogen managements on wheat straw decomposition and yield formation of mid-season Japonica rice

Objectives Under the wheat-rice rotation system, returning crop straws to field stands as an primary utilization method for wheat and rice straws. Nevertheless, the incorporation of wheat straw often exert a detrimental impact on the growth and development of succeeding rice crops, owing to its limited decomposition time. We conducted a study on nitrogen (N) management strategies aimed at fostering rice growth and accelerating wheat straw decomposition and nutrient release.

Methods Using rice cultivar ‘Hongyang 5’ as the test material, a two-year field experiment (2022−2023) was conducted in Yangzhou, Jiangsu. Under conditions of wheat straw incorporation amount 9900 kg/hm² and total N application rate 270 kg/hm², five nitrogen management treatments with varying N ratios of basal: tillering: panicle fertilizers were established, including 3∶3∶4 (T1), 3.5∶3.5∶3 (T2), 4∶4∶2 (T3), 4.5∶4.5∶1 (T4), and 5∶5∶0 (T5), alongside a no-N control (CK). Tillering dynamics were monitored from the beginning until stabilization. Rice population growth, dry matter accumulation, and N uptake were measured at key growth stages. Simultaneously, 100 g straw samples in nylon mesh bags were buried at a 5 cm depth of each treatment plot, with 9 bags per plot. The straw bags were retrieved at jointing, heading, and maturity stages to quantify straw decomposition (via weight loss) and N release (based on straw N content).

Results Among N management treatments, rice yield, effective panicles per unit area, spikelet number per panicle, and seed-setting rate followed a parabolic trend with rising basal−tillering N ratio. T2 achieved the highest values. Over both years, T2 also exhibited the highest productive tiller rate and total dry matter accumulation, increased by a maximum of 26.46% and 10.80% on average, respectively, compared to other treatments. Straw decomposition and decomposition proportion during the transplanting−jointing stage increased with higher basal−tillering N ratios but declined gradually in jointing−heading and heading−maturity stages. Cumulative N release rates from wheat straw were 67.50%−70.32% (2022) and 72.88%−76.13% (2023), with T3 and T5 showing the highest averages. Rice N use efficiency (NUE) was 28.11%−44.79% across treatments, peaking at 44.26% under T2. During jointing−heading and heading−maturity stages, straw decomposition, decomposition proportion, and N release rates decreased with increasing basal−tillering N ratios. Excessive basal−tillering N suppressed N uptake and utilization in later growth stages, ultimately reducing NUE. Correlation, factor, and redundancy analyses confirmed that appropriate panicle fertilizer application mitigated N competition between soil microbes and rice plants during late growth stages, enhancing plant N content, N accumulation, seed-setting rate, and thereby boosting both yield and NUE.

Conclusions Under full wheat straw incorporation in the rice-wheat rotation system of Jiangsu Province, allocating 70%−80% of total N (270 kg/hm²) in medium-japonica rice season as basal-tillering fertilizer and 20%−30% as panicle fertilizer effectively promotes wheat straw decomposition and N release, facilitates dry matter accumulation and grain filling, and achieves synergistic improvement in rice yield and nitrogen use efficiency.