Due to the large amount of nitrogen loss from crop production and the difficulty of controlling it, since 2015, different levels of Chinese government implemented many regulations i.e. fertilizer application strategy adjustments to reduce nitrogen loss. However, there lacks an exploration of the policy-driven changes in organic fertilizer substitution varying in nitrogen loss risk. Therefore, multiple surveys of fertilizer application strategy with diverse farming scale were carried out in Jinting Town of Suzhou City from 2015 to 2023. Based on the data of nitrogen input intensity and organic fertilizer substitution rate, the policies' responses resulting in nitrogen loss reduction were studied and analyzed in each crop types with different management models. The results showed the national "Two Actions" plans (based on 2020 ' s data) and Jinting's organic fertilizer subsidy policies (based on 2023 ' s data) reduced the nitrogen loss per unit weight crop yield by 14 % and 39 % respectively, though the nitrogen loss per unit area didn't pose a major change. Compared to smallholders' farms, scale farms showed greater environmental and economic advantages in lowering nitrogen loss risk and applying organic fertilizer. We concluded that the appropriate organic fertilizer substitution rate for each crop type is crucial to further reducing nitrogen loss and also guarantees crop yield, and scale farms should be the mainly entities of implementation of optimization fertilizer policy to achieve sustainable agricultural development in China.

(1) Background: Excessive nitrogen (N) fertilizer application in tea plantations leads to challenges such as soil acidification and nitrogen loss, impending the sustainable development of the plantation system. Yet, there is a lack of research on blended fertilization strategies, and limited data regarding N loss when substituting with organic fertilizer. (2) Methods: A year-long field monitoring experiment was conducted to evaluate the effects of substituting compound fertilizer with organic fertilizer, specifically with respect to runoff N loss and uptake of chemical fertilizer N by tea trees. (3) Results: The annual runoff N loss ranged from 0.16 to 0.57 kg·hm−2 and accounted for a mere 0.22–0.48% of N from fertilizer applications. Substitution with organic fertilizer reduced runoff N loss by 21–53% and improved the tea tree utilization efficiency of chemical fertilizer N from 16% to 27%. A 50% organic fertilizer substitution (based on the amount of N) promoted a net soil N mineralization rate, creating an ammonium-rich environment favored by tea trees. (4) Conclusions: The positive effects of partially substituting N fertilizer with organic fertilizer in tea plantation systems on both N utilization efficiency and N loss were confirmed. If conditions permit, the study team would aim to expand the temporal scope of the study, and to investigate the impact of organic fertilizer substitution on N loss under various precipitation intensities.

The intensity of crop farming fertilizer input is generally high in the Taihu Lake Region, with chemical fertilizer as the main form. Due to inappropriate fertilizer application, nitrogen and phosphorus loss have occurred, causing serious agricultural non-point source pollution. The Ministry of Agriculture and Rural Affairs of China has launched the "zero-growth action for chemical fertilizer use" and "replacement action with organic fertilizer" ("two actions" for short) campaigns since 2015. Local agricultural sectors adjusted fertilizer application strategies of crop farming to respond to the call of two actions. However, the current research is still focusing on reducing the total amount of fertilizer application and increasing the area of organic fertilizer application, which is mainly based on grain crops. The study of agricultural environment problems is still lacking, especially in vegetable, orchard, and tea systems. Therefore, a study was carried out in the typical agricultural area of Suzhou City Wuzhong District from 2019 to 2021. Based on the data of the amount of nitrogen and phosphorus removal by harvest crops and soil nitrogen and phosphorus residual in paddy, vegetable, orchard, and tea systems, the loss was estimated. The responses of nitrogen and phosphorus loss from typical crop systems to fertilizer application strategy adjustments were studied through analysis of different factors. The results showed that fertilizer application rate was the key to control nitrogen and phosphorus loss. Additionally, the suitable replacement ratio of organic fertilizer could further reduce the loss risk. It should be noted that the urgent demand for nutrients in crop growth should be considered to determine the timing of organic fertilizer application, and agricultural machinery should be used to assist organic fertilizer application to reduce labor output if possible. Fertilizer efficiency was the core of environmental friendliness and economic benefits of crop farming. Hence, improving fertilizer efficiency should be the guidance of fertilizer application strategy adjustment. Our suggestions on the adjustment of fertilizer application strategy in different crop systems in the study area are as follows:attention should be paid to the nitrogen, phosphorus, and potassium input ratio in paddy systems to further reduce nitrogen and phosphorus loss. Planting structure adjustment should be emphasized in vegetable systems to promote fertilizer efficiency. The strategy to satisfy both tea and orchard growth from a composite system perspective would help to build crop systems that meet the needs of green agricultural development.

为促进稻田化肥减量,根据太湖地区有机物料资源的特征,选取本地区典型地力田块,开展植物源有机肥在稻田生产应用效应的研究.以当地常规施肥措施(有机无机复混肥追施配方肥)为对照,比较相同施氮量条件下植物源有机肥(菜籽饼与豆粕源有机肥)施用对水稻籽粒产量及其构成因子、干物质形成与积累量、养分吸收与利用效率以及土壤养分等的影响.结果表明,相较于当地常规施肥措施,植物源有机肥施用下水稻产量显著增加11.2％,结实率显著增加5.9百分点.植物源有机肥施用下水稻干物质质量较当地常规施肥措施呈明显增加的趋势,至成熟期显著增加7.5％.与当地常规施肥措施相比,植物源有机肥施用条件下的水稻吸氮总量和氮素收获指数无明显变化,但氮素籽粒生产效率显著增加6.0％;水稻吸磷总量降低4.8％,磷素籽粒生产效率和磷素收获指数显著增加8.5％和6.7百分点;水稻吸钾总量增加18.2％,钾素籽粒生产效率和收获指数降低11.3％和2.4百分点.由此可见,与当地常规施肥措施相比,稻田中植物源有机肥施用具有更好的稳产性、养分均衡性,养分利用效率较高,在中等地力及以上的稻田环境下施用植物源有机肥优势显著.

为继续深入推进"化肥零增长"行动,在江苏省苏州市吴中区开展了有机无机复混肥不同施用量在稻田的应用效果试验,比较了有机无机复混肥每667 m2纯氮用量为0、7.2、9.6、12、14.4、16.8 kg条件下水稻籽粒产量、产量构成因子、干物质形成与积累量、氮磷钾吸收量以及肥料利用效率等的变化.结果表明,随着有机无机复混肥用量的增加,水稻产量呈先上升后下降的趋势,每667 m2纯氮用量为14.4 kg时水稻产量较高,且具有较高的有效穗数、每穗实粒数和适宜的结实率,抽穗-成熟期累积的干物质量也为最高.随着有机无机复混肥用量的增加,水稻吸氮量和干物质生产效率增加,氮素籽粒生产效率先上升后下降,氮素收获指数下降;水稻对磷素的吸收和利用效率无明显变化规律;水稻吸钾量明显上升,钾素籽粒生产效率、干物质生产效率和收获指数下降.另外,水稻产量、氮素利用率均与施肥量呈显著的一元二次抛物线关系,根据曲线拟合方程可知,水稻获得最高产量的每667 m2有机无机复混肥纯氮适宜施用量为13.965 kg,这一施肥水平的氮素利用率为43.94％.因此,合理控制有机无机复混肥在水稻生产中的施用量是获得较高产量和提高氮肥利用率的重要措施,此研究可为有机无机复混肥在苏州吴中地区的施用提供参考.

农田耕地土壤质量对农业生产至关重要,也是农业面源污染防控指导的重要依据.摸清农田土壤养分现状,分析耕地土壤演变态势可为种植业绿色可持续发展提供科学指向.该文在太湖典型水网区苏州市吴中区设立研究样点,连续3年定时定点采集典型农田土壤样品,监测涉及到农业面源污染土壤指标,并基于基础评级法、单因子指标法和内梅罗指数法等3种科学评价方法对其指标进行评价.结果表明:以基础评级法来看,土壤pH值、土壤总氮和土壤有效氮年均值均处于等级Ⅱ及以上,土壤有机质年均值在第3年由等级Ⅱ降为等级Ⅲ,土壤有效磷年均值处于等级Ⅲ;以单因子指标法来看,土壤pH值和有机质年际之间呈现微弱变好趋势,土壤氮的情况较好且稳定,土壤有效磷是主要的短板,需要进行关注调控;以内梅罗指数法来看,17个监测点位综合评级全部为中级甚至高级.总之,该区域代表样点耕地土壤养分库存较好,宜进一步采取农业面源污染控制措施.

确定稻田的适宜氮肥投入量是保障耕地持续生产力和减少农业面源污染的关键,而土壤地力直接影响着作物产量与氮投入关系.以江苏省苏州市吴中区稻田系统为对象,调查了当前水稻的氮肥投入现状及产量水平,并对土壤地力进行了定量评估.在此基础上,因地制宜地设定针对不同土壤地力的生产目标,给出了不同土壤地力下的适宜氮肥推荐用量及氮肥施用类型,并估算出吴中区现有土壤条件下,高地力田块推荐产量为7.50～9.00 t/hm2,对应适宜氮肥投入量为140～ 240 kg/hm2;中地力田块推荐产量为6.00～8.25 t/hm2,对应适宜氮肥投入量为130～230 kg/hm2;低地力田块推荐产量为5.25～ 7.50 t/hm2,对应适宜氮肥投入量为130～ 200 kg/hm2.