Abstract: Using indoor constant temperature culture, two groups of experiments with five nitrogen fertilizer treatments of F1 (potassium nitrate), F2 (ammonium chloride), F3 (urea), F4 (potassium nitrate ∶ ammonium chloride ∶ urea = 1∶1∶2), and F0 (no nitrogen fertilizer) were set up. The first group was straw decomposition test to explore the effect of nitrogen on straw decomposition rate and straw nitrogen release rate. In the second group of experiments, five main treatments of exogenous nitrogen fertilizer were set up, as well as two sub-treatments of adding straw (SC) and not adding straw (CK), to explore the changes of readily oxidizable organic carbon (ROC), ammonium nitrogen (NH₄⁺ -N) and nitrate nitrogen (NO₃^--N) in soil. The results showed that the addition of nitrogen fertilizer had no significant effect on straw decomposition, but could increase the nitrogen release rate of straw. The addition of nitrogen fertilizer had no significant effect on ROC content, and the addition of straw increased ROC content and made ROC more stable during the culture process. The addition of nitrogen fertilizer had no significant effect on soil NH₄⁺-N content, and straw addition reduced soil NH₄⁺-N content. The addition of potassium nitrate and no nitrogen fertilizer reduced the soil NO₃^--N content, and the addition of urea, ammonium chloride and straw combined with nitrogen fertilizer increased the soil NO₃^--N content. Overall, through the reasonable combination of nitrogen fertilizer and straw management measures, it was more conducive to the enrichment of soil nitrogen.

Key words: nitrogen fertilizer, nitrogen release capacity, straw decomposition, straw return to the field, rice paddy soil