农业工程学报
農業工程學報
농업공정학보
2013年
19期
79-87
,共9页
灌溉%土壤%水分%硝态氮淋失%饱和导水率%空间变异%三维%Copula函数
灌溉%土壤%水分%硝態氮淋失%飽和導水率%空間變異%三維%Copula函數
관개%토양%수분%초태담림실%포화도수솔%공간변이%삼유%Copula함수
irrigation%soils%moisture%nitrate leaching%saturated hydraulic conductivity%initial soil water content%spatial variability%trivariate Copula function
硝态氮淋失是滴灌系统设计和运行管理需要考虑的重要因素。该研究构建了滴灌条件下的水氮运移模型，利用HYDRUS-2D软件进行了求解，模拟分析了田间尺度砂壤土饱和导水率和初始含水率空间变异对NO 3--N淋失率的影响，并利用三维Gumbel-Hougaard Copula函数构建了土壤饱和导水率、初始含水率和NO 3--N淋失率的联合分布函数，分析了给定土壤饱和导水率和初始含水率条件下NO 3--N淋失率超过某一阈值的条件概率。结果表明， NO 3--N淋失率概率密度函数可用指数函数表示；土壤饱和导水率和初始含水率的空间变异会明显增加NO 3--N淋失风险；NO 3--N淋失率超过给定阈值（6.4%，均质土壤条件下的NO 3--N淋失率）的条件概率基本随土壤饱和导水率和初始含水率的增大而增大。构建田间尺度土壤特性参数（如饱和导水率、初始含水率等）与NO 3--N淋失率的联合分布函数为研究多变量空间变异条件下NO 3--N淋失风险评估提供了参考。
硝態氮淋失是滴灌繫統設計和運行管理需要攷慮的重要因素。該研究構建瞭滴灌條件下的水氮運移模型，利用HYDRUS-2D軟件進行瞭求解，模擬分析瞭田間呎度砂壤土飽和導水率和初始含水率空間變異對NO 3--N淋失率的影響，併利用三維Gumbel-Hougaard Copula函數構建瞭土壤飽和導水率、初始含水率和NO 3--N淋失率的聯閤分佈函數，分析瞭給定土壤飽和導水率和初始含水率條件下NO 3--N淋失率超過某一閾值的條件概率。結果錶明， NO 3--N淋失率概率密度函數可用指數函數錶示；土壤飽和導水率和初始含水率的空間變異會明顯增加NO 3--N淋失風險；NO 3--N淋失率超過給定閾值（6.4%，均質土壤條件下的NO 3--N淋失率）的條件概率基本隨土壤飽和導水率和初始含水率的增大而增大。構建田間呎度土壤特性參數（如飽和導水率、初始含水率等）與NO 3--N淋失率的聯閤分佈函數為研究多變量空間變異條件下NO 3--N淋失風險評估提供瞭參攷。
초태담림실시적관계통설계화운행관리수요고필적중요인소。해연구구건료적관조건하적수담운이모형，이용HYDRUS-2D연건진행료구해，모의분석료전간척도사양토포화도수솔화초시함수솔공간변이대NO 3--N림실솔적영향，병이용삼유Gumbel-Hougaard Copula함수구건료토양포화도수솔、초시함수솔화NO 3--N림실솔적연합분포함수，분석료급정토양포화도수솔화초시함수솔조건하NO 3--N림실솔초과모일역치적조건개솔。결과표명， NO 3--N림실솔개솔밀도함수가용지수함수표시；토양포화도수솔화초시함수솔적공간변이회명현증가NO 3--N림실풍험；NO 3--N림실솔초과급정역치（6.4%，균질토양조건하적NO 3--N림실솔）적조건개솔기본수토양포화도수솔화초시함수솔적증대이증대。구건전간척도토양특성삼수（여포화도수솔、초시함수솔등）여NO 3--N림실솔적연합분포함수위연구다변량공간변이조건하NO 3--N림실풍험평고제공료삼고。
Drip irrigation has been recognized as an efficient method to improve water and nitrogen use efficiency. Nitrate leaching is becoming an important consideration for the design, operation, and management of drip irrigation systems. Recent studies have indicated that soil properties such as soil texture and saturated hydraulic conductivity could impose a significant effect on nitrate leaching. However, most of these studies were conducted on an assumption of homogeneous soil. In the current study, the effect of the spatial variability of soil properties on nitrate leaching was evaluated by a model that was established and solved numerically by using the HYDRUS-2D package. In the simulation, the statistical distribution of the saturated hydraulic conductivity and the initial soil water content in the field were assumed to be able to be represented by a logarithmic normal distribution and a normal distribution function, respectively. A moderate variability for both saturated hydraulic conductivity and initial soil water content were considered with the coefficient of variation (CV) of 0.40 and 0.15, respectively. One hundred samples of the spatial varied saturated hydraulic conductivity and initial soil water content at a given CV value were generated randomly by the Monte Carlo method. The nitrate leaching ratios for these randomly generated parameters of saturated and initial soil water content were determined by the numerical model. After the positive correlation between the nitrate leaching ratio and the saturated hydraulic conductivity and the initial soil water content was confirmed, a joint distribution function of saturated hydraulic conductivity, initial soil water content, and nitrate leaching ratio was constructed using a Gumbel-Hougaard trivariate copula function. The maximum likelihood approach was used to determine the parameters for the Gumbel-Hougaard trivariate copula function and the Kolmogorov-Smirnov test indicated that the empirical distribution of the nitrate leaching ratios could be well represented by the trivariate copula function with a root mean square error (RMSE) value of 0.046. To quantify the risk of nitrate leaching, the conditional probability distribution function of the nitrate leaching ratio under given saturated hydraulic conductivities and initial soil water contents was estimated from the derived joint distribution function. The results indicated that the probability density function of the nitrate leaching ratio could be represented by an exponential function and the variability of saturated hydraulic conductivity and initial soil water content imposed an important effect on the nitrate leaching. For the sandy loam soil having medium variabilities of saturated hydraulic conductivity and initial soil water content, the simulated nitrate leaching ratio reached 13.2%, being more than double of the value for the homogeneous soil (6.4%). The probability under the condition that the nitrate leaching ratio exceeds a given threshold (6.4%) generally increases with an increasing saturated hydraulic conductivity and initial soil water content. It might be concluded that constructing a joint distribution function between the nitrate leaching and soil properties in the field (e.g., saturated hydraulic conductivity and initial soil water content) is a promising method to assess the risk of nitrate leaching while the spatial variability needs to be considered.
