淹水条件下秸秆还田的面源污染物释放特征

通过模拟淹水实验，研究秸秆覆盖与秸秆深埋2种还田行为中N、P、COD等面源污染物的直接释放特征。结果表明，淹水条件下，上覆水TN浓度表现为淹水后一直持续下降，TP表现为急促上升后再持续下降，而COD则为缓慢上升后再下降。秸秆对TN的释放强度要高于TP；除了TP在淹水初期释放速率有所提高外，TN与COD的释放速率持续下降。秸秆覆盖时的面源污染物浓度高于秸秆翻埋；相同还田方式中，秸秆还田量越大，面源污染物浓度越高。从面源污染控制角度出发，淹水条件下秸秆TN防治的最佳时间为淹水初期，TP、COD为淹水后1—3周；最友好的还田方式为秸秆翻埋。试验结论为合理界定秸秆还田的负面效应，遏制秸秆还田造成的面源污染提供了依据。

Releasing characteristics of nonpoint source pollutants from straws under submerging condition

The manner of straw returning is a double-edged sword for cropland ecosystems because it can not only return nutrients for crop, enhance the soil fertility and lessen the use of chemical manures correspondingly, but also it may result in nonpoint source pollutants such as N, P and COD, which were released to water system in the process of its decomposition. How huge is the potential effect of the nonpoint source pollution when straws were applied to paddy fields? In this research, the simulated experiment under submerging condition was conducted to investigate the direct releasing characteristic of nonpoint source pollutants involving N, P and COD in the process of two methods about returned strew to soil such as surface cover (SC) and strew burying (SB). The results taking a period of 38 days showed that under submerging condition, the concentration of TN in surface water was decreased continuously, while TP, COD was increased urgently or slowly and then decreased continuously, respectively. The releasing intensity of TN was higher than that of TP, while the releasing speeds of TN and COD decreased continuously, except that the releasing speed of TP increased slightly at the beginning of submerging. The concentration of nonpoint source pollutants in the covering water of SC was more than that of SB, and it was increasing with the application amount. From the perspective of controlling the agricultural nonpoint source pollution, the appropriate time for TN prevention was in the initial stage of submerging, while the time for the TP and COD prevention was in 1~3 weeks after submerging. The strew burying was the friendly method. The above conclusion could provide the scientific basis for determining the negative effect of straw manure reasonably and limiting the nonpoint source pollution resulted from the returned straws to soil.