稻田-沟塘系统水氮动态模拟与灌排调控模型构建

Simulation of the water and nitrogen dynamics for paddy field-ditch pond system and model construction of irrigation and drainage regulation

沟塘系统对农田排水具有较好的拦蓄能力,是降低中国南方稻区农业面源污染风险的有效措施,定量化评价稻田-沟塘系统水氮过程是合理制定水氮管理措施的关键。该研究以稻田-作物模型WHCNS_Rice为基础,通过添加沟塘水氮平衡和灌排调控过程,构建了稻田-沟塘系统水氮调控模型。并采用太湖流域2 a不同灌排和施肥处理的田间试验数据校准和验证模型,分析不同灌排和施肥处理下稻田-沟塘系统的调控策略。研究结果显示,模型能够模拟不同灌排和施肥处理下稻田土壤含水量、稻田田面水深、径流量、氮素径流损失量、氨挥发量、作物吸氮量和作物产量,模拟的相对均方根误差、一致性指数和模型模拟效率的范围分别为4.6%~29.7%、0.758~0.996和0.073~0.983,均在可接受的范围内。模拟结果显示,与传统处理相比,控制灌溉结合优化施肥,减少了稻田32.1%~36.2%的灌溉水用量和36.7%~67.3%的氮素径流损失,同时平均降低了55.1%沟塘硝态氮浓度,从而降低了沟塘地表氮素径流损失风险。Morris敏感度分析结果显示,稻田土壤水力学参数和沟塘渗漏速率对沟塘水深的模拟影响较大,而作物参数的敏感度相对较低。沟塘硝态氮浓度对稻田水力学参数、沟塘氮素消纳系数和氨挥发一阶动力学系数较敏感。同时,构建的模型能反映不同水氮管理措施和沟塘/稻田面积比下稻田-沟塘系统水分消耗、氮素去向和作物生长过程。该模型可为优化稻田-沟塘系统水氮管理方案、防控农业面源污染提供有力工具。

The runoff nitrogen(N)loss of paddy fields is one of the major sources for agricultural non-point pollution(AGNPS)in the rice areas of southern China.In an effective way to reduce the AGNPS risk,a ditch-pond system can be used to intercept farmland drainage in recent years.It is necessary to quantify the water and N processes of the system for appropriate management practices.In this study,a new regulation model of water and nitrogen was developed for the paddy field-ditch pond system.The water and nitrogen processes of the ditch system incorporated the regulation of irrigation and drainage into the soil-rice system model(soil water heat carbon-nitrogen simulator for rice,WHCNS_Rice).A global Morris sensitivity analysis was adopted to evaluate the output responses of the model to different input parameters.The model was verified to utilize the dataset from a two-years(2009-2010)field experiment with the combination of two irrigation regimes(FI,traditional flooding irrigation;CI,controlled irrigation)and two N management(FP,farmer’s N practice;SP,site-specific N practice)in the Taihu Lake Basin.The specific parameters included the ponding water depth,soil water content,runoff,N runoff loss,ammonia volatilization,crop N uptake,and crop yield.The results showed that the Relative Root Mean Square Error(RRMSE),Index of Agreement(IA),and Nash-Sutcliffe Efficiency(NSE)ranged from 4.6%to 29.7%,0.758 to 0.996,and 0.073 to 0.983,respectively.The model performed well to simulate the water and N balances,as well as the rice growth for paddy field-ditch pond system under different irrigation regimes and N management practices.Morris sensitivity analysis showed that the soil hydraulic parameters of the paddy field and the leakage rate of the ditch(kr)presented the greatest influence on the simulation of water depth in the ditch,while the sensitivity of crop parameters was relatively low.The nitrate concentration in the ditch was also more sensitive to the hydraulic parameters of the paddy field,the coefficient of N reduction(RD)in ditches,and the first-order kinetic coefficient of ammonia volatilization(Kv).At the same time,the improved model was utilized to clarify the effects of ditch pond/paddy field area(β),irrigation regimes,and N management practices on water consumption,N fate,and crop growth in the paddy field-ditch pond system.Furthermore,the calibrated and validated model was selected to evaluate the effects of different water and N management on water and N balances of the paddy field-ditch pond system.It was found that the combination of controlled irrigation and site-specific N management significantly reduced irrigation water use and N runoff loss by 32.1%-36.2%and 36.7%-67.3%,respectively.Meanwhile,the nitrate concentration in the ditch pond was reduced by 55.1%,leading to a significant decrease in the N loss risk of the paddy field-ditch pond system.