青铜峡灌区水稻田化肥氮去向研究

青铜峡灌区是我国古老的特大型灌区和粮食主产区之一,灌区农田氮肥的过量施用已经导致化肥氮向水体流失.用15N示踪微区试验方法研究了青铜峡引黄灌区习惯灌溉量条件下水稻田化肥氮素去向.结果表明,施氮量为当地习惯施氮300kg.hm-2时,水稻吸收的化肥氮在籽粒中最多,氮肥的当季利用率为45.93%,吸收的土壤氮约占52.63%;作物中的回收率为27.90%,在0～90cm土壤中的残留率为23.31%,作物-土壤体系中的回收率为51.21%,氮肥的损失率为48.79%;氮肥除了被当季作物吸收和部分以矿质氮残留在土壤中外,灌区19×104hm2的水稻田化肥氮年流失量为2.78×104t,生产1000kg水稻(净籽粒),排放纯氮20.17kg;在0～90cm土壤层中均有化肥氮残留,残留化肥氮主要富集在表层0～30cm,在60～90cm检测到化肥氮,说明青铜峡引黄灌区在习惯灌溉量条件下,水稻田当季的化肥氮淋溶到90cm以下,成为浅层地下水的潜在污染源.

The fate of fertilizer-derived nitrogen in a rice field in the Qingtongxia irrigation area

Nitrogen cycling in natural environments has been seriously disturbed due to fertilizer overuse or misuse. Some nitrogen oxides in the imbalanced nitrogen cycle are main contributors for major environmental problems like water eutrophication. Nitrate leaching from agricultural lands during the growing season and its threat to water quality is an important global environmental issues. Field experiments were carried out at a rice field in the Ningxia Hui Autonomous Region in northwestern China to provide information on the fate of (fertilizer-derived nitrogen) FDN in the Qingtongxia irrigation area of the upper Yellow River basin. We used the stable isotope 15N to trace the fate of the applied nitrogen fertilizer. The fertilization levels in this study were 0, 240 and 300 kg·hm-2. We estimated the recovery of FDN in root, stover and grain of rice and profile distribution of fertilizer nitrogen residue in soil. The results showed that the uptake of FDN in grain was increased by higher N application rate. At a high level of fertilization (300 kg·hm-2), nitrogen uptake from fertilizer by the rice plant at harvest is 45.93%, percentage of N in the plant tissue derived from the soil is 52.63%, recovery by rice is 27.90%, soil residual N is 23.31%, the combined recovery of rice and soil is 51.21%, and the loss rate of nitrogen fertilizer is 48.79%. Based on statistical data, 500 million kg of nitrogen fertilizer is used in the Ningxia Hui Autonomous Region each year. Its loss from rice fields in one growing season is 27.81 million kg. To produce 1000 kg rice, the nitrogen loss is 20.17 kg. Soil residues of nitrogen fertilizer were also measured even to a soil depth of 60~90 cm, indicating that nitrogen fertilizer leaching could be a pollution source for underground water.