秸秆还田是实现农学和环境双赢的重要途径。然而，在表层土壤（0-20 cm）中，最佳稻草替代氮磷肥料量仍不清楚。因此，我们在 2016-2018年进行了三年的田间试验，探讨不同秸秆用量替代肥料中氮磷对水稻收获后土壤理化性质、土壤有机碳（SOC）储量、土壤氮残留、土壤磷残留、水稻产量、产量构成、氮（N）肥利用效率和磷（ P) 肥利用效率的影响。与单施化肥相比，5 t ha^-1秸秆替代氮磷肥提高了水稻穗粒数、有效穗数、结实率、千粒重和籽粒产量，也增加了水稻地上氮磷养分吸收量。同时，秸秆用量超过 2.5 t ha^-1 比单施化肥处理增加了土壤有效氮磷钾含量。此外，与单施化肥处理相比，所有秸秆替代氮磷处理均提高了土壤有机碳储存量。相比单施化肥处理，5 t ha^-1秸秆替代氮磷肥使土壤中氮残留和磷残留分别减少了 68.3% 和 28.9%。同时，水稻地上氮磷养分吸收和土壤理化性质共同解释了19.3%的水稻籽粒产量和产量构成的变化。综上，5 t ha^-1秸秆替代氮磷肥是一种合理的施肥制度，不仅可以提高土壤理化性质、土壤有机碳固存、水稻产量、产量构成、氮肥利用效率和磷肥利用效率，同时可以降低环境污染的风险。

Improving nitrogen use efficiency (NUE) and decreasing N loss are critical to sustainable agriculture. The objective of this research was to investigate the effect of various fertilization regimes on yield, NUE, N agronomic efficiency (NAE) and N loss in long-term (16- or 24-yr) experiments carried out at three rice-wheat rotation sites (Chongqing, Suining and Wuchang) in subtropical China. Three treatments were examined: sole chemical N, N+phosphorus (NP), and NP+potassium (NPK) fertilizations. Grain yields at three sites were significantly increased by 9.3-81.6% (rice) and 54.5-93.8% (wheat) under NP compared with N alone, 1.7-9.8% (rice) and 0-17.6% (wheat) with NPK compared with NP. Compared to NP, NUE significantly increased for wheat at Chongqing (9.3%) and Wuchang (11.8%), but not at Suining, China. No changes in NUE were observed in rice between NP and NPK at all three sites. The rice-wheat rotation’s NAE was 3.3 kg kg-1 higher under NPK than under NP at Chongqing, while NAE was similar for NP and NPK at Suining and Wuchang. We estimated that an uptake increase of 1.0 kg N ha-1 would increase 40 kg rice and 30 kg wheat ha-1. Nitrogen loss/input ratios were ~60, ~40 or ~30% under N, NP or NPK at three sites, indicating significant decrease of N loss by P or PK additions. We attribute part of the increase in NUE soil N accumulation which significantly increased by 25-55 kg ha-1 yr-1 under NPK at three sites, whereas by 35 kg ha-1 yr-1 under NP at Chongqing only. This paper illustrates that apply P and K to wheat, and reduce K application to rice is an effective nutrient management strategy for both the NUE improvement and N losses reduction in China.

Long-term fertilization experiment provides the platform for understanding the proton budgets in nitrogen transformations of agricultural ecosystems. We analyzed the historical (1990-2005) observations on four agricultural long-term experiments in China (Changping, Chongqing, Gongzhuling and Qiyang) under four different fertilizations, i.e., no-fertilizer (control), sole chemical nitrogen fertilizer (FN), sole chemical phosphorous and potassium fertilizers (FPK) and chemical nitrogen, phosphorous and potassium fertilizers (FNPK). The significant decline in topsoil pH was caused not only by chemical N fertilization (0.29 and 0.89 ΔpH at Gongzhuling and Qiyang, respectively) but also by chemical PK fertilization (0.59 ΔpH at Gongzhuling). The enhancement of available nutrients in the topsoil due to long-term direct nutrients supply with chemical fertilizers was in the descending order of available P (168-599%)>available K (16-189%)>available N (9-33%). The relative rate of soil pH decline was lower under long-term judicious chemical fertilization (-0.036-0.034 ΔpH yr-1) than that under long-term sole N or PK fertilization (0.016-0.086 ΔpH yr-1). Long-term judicious chemical fertilization with N, P and K elements decreases the nutritional limitation to normal crop growth, under which more N output was distributed in biomass removal rather than the loss via nitrate leaching. We concluded that the N distribution percentage of nitrate leaching to biomass removal might be a suitable indicator to the sensitivity of agricultural ecosystems to acid inputs.