Effects of organic fertilizer substitution strategies on nitrogen loss from crop production in Taihu Lake Basin: A case study of Jinting Town, Suzhou, China

• Driven by the national “Two Actions” plans and Jinting Town's organic fertilizer subsidy policies, the nitrogen loss amount per unit weight crop yield in 2020 and 2023 reduced by 14 % and 39 % respectively compared with 2015. • Scale farming management could lower nitrogen loss amount per unit weight crop yield by 8 % to 40 % compared with smallholding. • The appropriate organic fertilizer substitution rate for each crop type is crucial to further reducing nitrogen loss and also guarantees crop yield after cutting nitrogen input intensity. 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.