华北平原农田硝态氮淋溶率和淋溶负荷估计

由于化肥过度施用且强度逐渐增加,华北平原氮淋溶问题日趋严重且造成了地下水污染风险.利用1991年以来公开发表的文献中290 组农田NO₃^--N 淋溶试验样本(淋溶率和10个影响因素),基于Bayesian递归回归树模型初步建立了华北平原农田NO₃^--N淋溶迁移过程统计模型.以2008年为例,基于华北平原县域合成氮肥、复合肥施用量和1 km×1 km的影响因素和土地利用(耕地)数据,最终得到1 km×1 km的华北平原农田NO₃^--N淋溶率和淋溶负荷及其不确定性水平.初步结果表明:①模型校准和验证R²分别达到0.832和0.829,模拟结果相对可靠;②华北平原耕地NO₃^--N的淋溶率具有显著的空间分异,其中位值为15.4%(R₅₀为12.6%~18.2%),其主要影响因素为土壤TN量、施N量、灌溉比例与降雨量的比值等;相应地,2008年淋溶负荷和淋溶量分别为995.1 Gg·a^-1(833.4~1156.7 Gg·a^-1);③NO₃^--N淋溶率较高的区域集中在太行山脉以东、黄河附近以及苏北的县(区、市),淋溶负荷贡献最大为河南(~37.7%)、江苏(~24.8%)和河北(~21.6%).

Estimation of nitrate leaching rate and loading deduced by agricultural fertilizers in the North China Plain

Nitrogen leaching and the associated groundwater crisis in the North China Plain (NCP) become extremely severe because of the increasingly excessive fertilization of wheat-maize crop systems. 290 leaching measurements for agricultural fields in the NCP were summarized based on the 29 journal articles published from 1991 to 2013;correspondingly, a statistical model was then developed for NO₃^--N leaching transport processes using Bayesian Recursive Regression Tree approach. The calibrated BRRT-deduced statistical model was eventually applied to estimate the 1 km×1 km nitrate leaching rate and loading deduced by agricultural fertilizers in the North China Plain in 2008, using the county-based synthetic and compound fertilizers as well as 1 km×1 km resolution independent variables and cropland datasets. The preliminary results include that: (i) the coefficients of determination (R²) reached 0.832 and 0.829 for model calibration and verification steps, respectively. Thus, the calibrated BRRT-deduced statistical model was to an extent reliable for spatial simulations;(ii) the nitrate leaching rate was spatially heterogeneous across the NCP's cropland and its median equaled to 15.4 with the interquartile range from 12.6%~18.2%, while the factors that significantly influenced nitrate leaching rate were soil N content, N application rate, water input (=irrigation rate/precipitation), etc, with the corresponding nitrate leaching loading in the NCP as 995.1 Gg·a^-1 (833.4~1156.7 Gg·a^-1);(iii) the hotpots with higher nitrate leaching rate were located along the eastern Taihang Mountains, downstream of Yellow River Basin and northern Jiangsu Province, while the major contributions for nitrate leaching loading in the NCP were from Henan (~37.7%), Jiangsu (~24.8%) and Hebei (~21.6%) Provinces.