秸秆还田条件下稻田田面水不同形态氮动态变化特征研究

Study on dynamics of Nitrogen in different forms in surface water of paddy field under straw return

为探索巢湖流域稻麦（油）轮作区水稻季减少农田氮素流失的有效耕作措施，降低其对湖区水质的威胁，采用野外定位观测试验并结合室内实验分析，研究了连续两年秸秆还田条件下稻田田面水总氮（TN）、溶解态氮（DN）、溶解态有机氮（DON）、铵态氮（NH4^＋-N）和硝态氮（N03^--N）浓度的动态变化特征。结果表明，稻田施用尿素后第2天或第4天田面水的TN、DN、DON和NH4^＋-N浓度达到峰值，然后随着时间的推移迅速降低，至8～10d后趋于稳定；在整个水稻生育期内，NO3^--N浓度普遍较低；尿素施用后8～10d之内是控制稻田氮素流失的关键时期，秸秆还田降低这一时期TN、DN、NH4^＋-N浓度的效果显著，而DON浓度差异未达显著水平。DN是稻田田面水氮素存在的主要形态，所占TN比例达63．2％～88-8％，尿素施用后6d内DN又以NH4^＋-N为主，NH4^＋-N所占TN的比例为33．8％-69．9％。DON是稻田田面水氮素的重要组成部分，其生态环境效应不容忽视。秸秆还田还有利于水稻产量的提高，增产幅度分别为12．25％和7．68％，平均为9．96％。在保证水稻产量的前提下，秸秆还田可以作为控制稻田氮素流失的措施在巢湖流域使用。

In order to explore the effective tillage for reducing nitrogen losse and improving lake water qual-ity, field experiments were conducted to study the dynamics of TN （total nitrogen）, DN （dissolved nitro-gen）, DON （dissolved organic nitrogen）, ammonia nitrogen （NH4^＋-N） and nitrate nitrogen （NO3^--N） concen- trations in surface water of paddy field in the Chaohu Lake region in two consecutive years. The results show that the concentrations of TN,DN,DON and NH4^＋-N in surface water reached the maximums after 2 or 4 days of urea application, then declined rapidly, and finally leveled off after 8-10 days. The NO3^--N concentration remained at a low level during the whole rice growing seasons, although it showed a little raise after 4 or 6 days of urea application. Obviously, it is the critical period for controlling N loss from paddy field within 8-10 days after urea application. Straw return could effectively decrease the higher con-centrations of TN, DN and NH4^＋-N in surface water during the earlier stage, whereas the differences in DON concentration was not so significant. Therefore, straw return is beneficial for lowering the potential risk of N loss. Furthermore, DN was the predominant form of TN in surface water, which accounted for 63.2 %-88.8 % of the TN. Within 8 days after urea application, the proportion of NH4^＋-N to TN was 33.8 %-69.9 %. DON was a significant component of TN in surface water, which suggested that its ecologi-cal and environmental effects should not be neglected. The results also show that the rice yields of CTS in-creased significantly by 12.25 % and 7.68 % compared with CT, which indicated that straw return could in- crease the rice yields. The findings indicate that assuring the production of rice yields, straw return ap-peared to be an effective measure for the source control of the nitrogen loss from paddy field in the Chao-hu Lake region.