富营养化河水灌溉对稻田土壤氮磷养分贡献的影响——以太湖地区黄泥土为例

以太湖地区主要稻田土壤类型黄泥土为对象,利用当地富营养化河水对回填土柱和植稻原状土渗漏池进行模拟稻田灌溉试验,系统研究了灌溉水对稻田土壤氮磷营养的贡献.在回填土柱灌溉试验中,在试验初期,不同形态的氮素均有较高的淋失量,以后逐渐降低,表明初期淋失的氮素主要来自土壤,而不是灌溉河水.在整个水稻生长季,均观测到有可溶性有机氮淋失,表明富营养化河水灌溉条件下可溶性有机氮是稻田土壤主要的氮素淋失形态.在本试验中,磷素的淋失动态与氮素的淋失动态截然相反,淹水后很长一段时间内均没有土壤磷素淋失,但在淹水灌溉后期有大量的土壤磷素淋失损失,这可能是淹水后期土壤对磷的吸持已达到饱和状态,不能继续固持土壤中多余的磷所致.与回填土柱模拟灌溉淋洗试验相比,在当前供肥条件下,原状土渗漏池试验氮磷淋失量远低于回填土柱试验,而灌溉水对土壤氮磷养分的贡献远高于回填土柱.通过富营养化河水灌溉带入当季稻田的N量达到每公顷56.3 kg,其中有55.8 kg N可被土壤吸持和作物吸收,表明太湖地区稻田土壤对氮磷养分来说是一个环境友好的生态系统.在利用当地富营养化河水进行稻田土壤灌溉时可适量减少肥料施用量、优化氮磷肥料管理.

Contribution of nitrogen and phosphorus on eutrophied irrigation water in a paddy Soil: a case study in taihu Lake Region

In the Taihu Lake region, the neighboring eutrophied river water is widely used to irrigate the paddy field. Both refilled and monolith lysimeter experiments were adopted to simulate the irrigation system to study the contribution of eutrophied irrigation water to nitrogen (N) and phosphorus (P) in a paddy soil. In the repacked soil column experiment with regular irrigations, N leaching losses were high in the beginning of the flooding period, and decreased gradually to around zero indicating that N leaching at the beginning flooding stage came mostly from native soil N not N in the irrigation water. The dissolved organic nitrogen (DON), however, was steadily detected throughout the whole flooding period indicating that the leaching loss of DON was mainly from the input from river water irrigation. Contrary to the N leaching pattern, an obvious P leaching loss was observed only after a long time of flooding indicating that continuous P input from eutrophied irrigation water led to saturation of soil P absorption after a long time flooding treatment. In comparison to the repacked soil column experiment, with local fertilizer application rate, the leaching losses of N and P were lower in the undisturbed lysimeter experiment and the contributions of eutrophied irrigation water were higher to the N and P in paddy soil. Among the 56.3 kg N/hm2 of input from irrigation water, there was totally 55.8 kg N/hm2could be attributed to soil retention and rice plant uptake, indicating that paddy soil might serve as an environmentally friendly ecosystem in N and P absorption as eutrophied irrigation water in Taihu region concerned. Furthermore, N and P fertilizer application rate could be decreased accordingly to optimize fertilizer management when contributions from eutrophied irrigation water were taken into consideration.