保护性耕作对冬小麦-夏玉米农田氮肥氨挥发损失的影响

【目的】保护性耕作有利于水土保持和提高土壤有机碳库，而对氮素氨挥发的影响并不是很清楚。研究长期定位试验下华北农田施肥后氨挥发发生规律，探索保护性耕作条件下的氮素利用率。【方法】采用间歇动态箱式法对翻耕、旋耕和免耕3种耕作方式下冬小麦-夏玉米农田氨挥发通量及其影响因素进行比较研究。【结果】相对于翻耕和旋耕处理，免耕显著促进了小麦季和玉米季地表追肥的氨挥发，但显著降低了小麦基肥期的氨挥发速率。翻耕、旋耕和免耕下小麦-玉米全生育期氨挥发损失量为15.8、18.4和28.6 kg?hm-2?a-1，分别占施肥量的4.9%、5.7%和8.8%。实验室培养分析表明，免耕和旋耕显著提高了表层（0—5 cm）土壤脲酶活性，加速尿素水解为NH4+，从而促进氨挥发。【结论】免耕条件下，肥料表施易发生氨挥发，采用一次性深施是减少免耕氨挥发的有效途径之一。

Effect of Conservation Tillage on Ammonia Volatilization from Nitrogen Fertilizer in Winter Wheat-Summer Maize Cropping System

【Objective】Conservation tillage is usually less prone to erosion and has a great soil organic matter content as compared to conventional tillage. However, the effect of conservation tillage on the ammonia volatilization is not well understood. In this study ammonia volatilization under conservation tillage was investigated to provide new strategies for improving nitrogen use efficiency. 【Method】Continuous air-flow enclosure method was used to monitor ammonia volatilization under three tillage systems (No-tillage, NT; rotary tillage, RT; conventional tillage, CT) in a winter wheat and maize rotation in northern China. 【Result】Compared to CT and RT, NT significantly increased NH3 volatilization when nitrogen was top-dressed, reduced NH3 volatilization when nitrogen was incorporated into soil. In the winter wheat-summer maize cropping season, the cumulated NH3 volatilizations of two seasons was 15.8, 18.4 and 28.6 kg?hm-2?a-1 under CT, TR and NT, accounting for 4.9%, 5.7%, and 8.8% of the applied fertilizer, respectively. Laboratory incubation study showed that higher urease activity in surface soil resulted in rapid urea hydrolysis, which stimulated NH3 volatilization under NT. 【Conclusion】In the North China Plain, soil under NT soils are prone to NH3 volatilization following surface application of urea, and one-time deep application of nitrogen is recommended for reducing ammonia volatilization under no-tillage system.