太湖地区直播稻田氮素渗漏损失试验研究

在太湖流域丹阳地区，通过田间试验研究了旱直播稻田氮素的渗漏损失特征。结果表明，在当地正常的水肥管理模式下，旱直播稻田氮素的渗漏主要发生在水稻生长前期，施入的基肥不易迅速水解，部分仍滞留在表层土壤，灌溉或强降水时增大了氮素渗漏流失的风险。稻田40 cm深度土壤硝态氮和铵态氮浓度平均值分别为5.79和0.49 mg/L，硝态氮浓度最大值出现在苗肥施入后的第7 d，达到21.8 mg/L。以土壤深度40 cm为界面计算的氮素渗漏通量表明，铵态氮和硝态氮在整个稻季的平均渗漏量为N 3.8和28.4 kg/hm2，氮素渗漏的形式主要为硝态氮。直播水稻萌芽至幼苗期对氮素的吸收量少，应适当减少前期基肥或苗肥的施用量，充分利用基肥与苗肥的叠加效应，减少前期氮素渗漏流失。

Experimental study on nitrogen leaching in a direct-seeding rice paddy of Taihu Lake Basin

Field experiment of nitrogen leaching loss in a dry direct-seeding rice paddy was conducted in Danyang region of Taihu Lake Basin. Results show that the nitrogen leaching loss is mainly occurred during the early stage of rice growing season under local water and fertilizer management, especially for the seedling fertilization. The base fertilization has not rapidly hydrolyzed without standing water in about two weeks after rice is sowed, that resulted in part of the fertilizers still exists in surface soil. Even though part of the base fertilizers is transformed into nitrate-nitrogen in wet soil, the nitrate nitrogen still resides in surface soil without downward water-leaching. Both the residual base fertilizers and the added seedling fertilizers increase the chance of nitrogen leaching loss when irrigation or precipitation occurred. The mean concentrations of ammonia-nitrogen and nitrate-nitrogen, at 40 cm soil depth, are 5.79 and 0.49 mg/L respectively, and nitrate-nitrogen is the main part of nitrogen loss through leaching, whose maximal concentration is 21.8 mg/L on day 7 after the seedling fertilization. The mean quantities of leaching loss of ammonia-nitrogen and nitrate-nitrogen at soil depth of 40 cm, in the whole rice growing season, are about N 3.8 and 28.4 kg/hm² respectively, which indicate that the nitrate-nitrogen accounts for a majority proportion. As a result, in direct-seeding rice paddies, the superposition effect of both base and seedling fertilizers should be paid more attention. Due to the low nitrogen-uptake of rice at its seedling stage, the prophase fertilizers may be advisably reduced to decrease the risk of nitrogen leaching.