Effect of straw and inhibitors on the fate of nitrogen applied to paddy soil

A pot experiment was used to explore the distribution of fertilizer nitrogen and agronomic effects in a paddy soil–rice system under five treatments: no N, straw or inhibitor (C), urea (U), urea + straw (US), urea + urease + nitrification inhibitor (UI), and urea + urease + nitrification inhibitor + straw (UIS). Soil and urea-derived microbial biomass N increased significantly in US and UIS at seedling and tillering, indicating a strong biotic role in retaining fertilizer N with straw addition. About 10% of urea-N was recovered as fixed ammonium (FA) at seedling and was subsequently released at tillering and maturation across treatments, emphasizing FA’s importance in N retention and supply. Compared with U, rice yield and N uptake in US decreased by 7.8% and 25.2%, respectively, while inhibitors (UIS) alleviated these reductions by 16.4% and 31.6%. UIS is recommended as the most appropriate strategy for paddy soils of Northeast China based on N dynamics, though economic effects and field-scale validation require further evaluation.