基于11年定位试验，研究长期秸秆还田（CFS）对田面水的化学需氧量（COD）、氮（N）、磷（P）等水环境风险指标变化规律及对水稻产量的影响。结果表明，与CF处理（秸秆不还田）相比，CFS处理水稻减产3.5%，但差异不显著，主要是因为秸秆还田减少了水稻有效穗数。与CF处理相比，CFS处理田面水中总氮（TN）、总磷（TP）含量呈先下降后上升趋势，还田初期田面水中NH₄⁺-N（铵态氮）/TN降低，田面水中COD平均增加69.4%，水环境风险上升。但CFS处理田面水中COD仍低于GB 5084—2021《农田灌溉水质标准》的水田作物灌溉水质要求（COD为150 mg/L）。说明长期秸秆还田降低了还田初期田面水中N、P的水环境风险，但增加了田面水中COD的水环境风险，而对水稻产量影响不显著。

The effects of long-term straw return to the field (CFS) on the changes of water environment risk indicators such as chemical oxygen demand (COD), nitrogen (N) and phosphorus (P) in surface water and rice yield were studied by 11-year positioning experiment. The results showed that compared with CF treatment (without returning straw to the field), CFS treatment reduced rice yield by 3.5%, but the difference was not significant, mainly because CFS treatment reduced the number of effective ears of rice. Compared with CF treatment, the content of total nitrogen (TN) and total phosphorus (TP) in surface water treated with CFS showed a trend of first decreasing and then increasing, while the ammonium nitrogen (NH₄⁺-N) /TN in the surface water at the initial stage of return to field was decreased, but the aquatic environment risk of COD in the surface water was increased by 69.4% on average. However, the COD of field surface water of CFS treatment was lower than the water quality requirement of paddy field crop irrigation in the national standard “Farmland Irrigation Water Quality Standard” (GB5084—2021) (COD is 150 mg/L). Therefore, the CFS treatment reduced the water environment risk of N and P in the surface water at the initial stage of straw return to the field, and increased the water environment risk of COD in surface water, but had no significant effect on rice yield.