河套灌区土壤水盐和作物生长的HYDRUS-EPIC模型分布式模拟

土壤水盐是影响干旱灌区作物产量的主要因素。分布式模型可综合考虑土壤、水文和气象因子在灌区的时空变异特征,为评估区域尺度土壤水盐与作物生长状况提供有效工具。该文以河套灌区解放闸灌域为研究区,根据气象-土壤-作物-灌溉等因子的空间分布特征进行均质单元划分,建立基于一维农业水文模型HYDRUS-EPIC的灌区尺度分布式模型。利用2012年和2013年定点观测数据(土壤水分、盐分、叶面积指数和作物产量)进行模型率定与验证;进一步应用模型以求探明现状灌溉条件下研究区土壤水盐与作物生长状况及存在的问题。结果表明:生育期内灌区根区土壤(0~100 cm)有效饱和度为0.44~0.90,基本满足作物耗水需求;根区土壤溶液平均盐分浓度为3.1~13.5 g/L,相应地作物的相对产量为0.35~1.33,土壤盐分过高成为限制研究区作物产量的主因。为调控根区土壤水盐状况,对地下水深埋区(东北部)需进行灌水量的适宜补充,宜将浅埋区(西北、西南等)地下水平均埋深控制在1.3 m以下。

Distributed modeling of soil water-salt dynamics and crop yields based on HYDRUS-EPIC model in Hetao Irrigation District

Abstract: Soil moisture and salinity are two key factors for crop production in arid irrigation districts. It is critical to modify soil water-salt dynamics and crop growth on a regional scale for the sustainable agriculture. In this paper, a distributed agro-hydrological model that well considers the spatial variability of soil and hydrological factors was developed to simulate soil water movement, solute transport and crop growth process on the regional scale. Jiefangzha Irrigation System (JIS) of the Hetao Irrigation District was selected as the study area. The JIS was divided into 201 homogeneous simulation units based on the combinations of weather-soil-crop-irrigation. In this way, the one-dimensional agro-hydrological model-HYDRUS-EPIC (HYDRUS-1D coupled with EPIC crop growth module), was used and expanded to the regional scale. Field experiments were conducted in 2012 and 2013. The dataset of soil moisture, soil solute concentration, leaf area index (LAI) and crop yield were collected at 40 monitoring points, and used for model calibration and validation. Simulated soil moisture and salinity concentration in the root zone showed good agreement with the measured values. During the calibration process, root mean square error (RMSE), mean relative error (MRE) and coefficient of determination (R2) for soil moisture were 0.03 cm3/cm3, 0.3% and 0.67, respectively. For salinity concentration, RMSE, MRE and R2 were 2.72 g/L, -13.5% and 0.53. LAI and crop yields were fitted well with the observations. MRE values for the estimated and measured LAI and crop yields were 1.0% and 1.1%, and R2 were both larger than 0.90 for these two items. During the validation process, RMSE, MRE, and R2 were 0.04 cm3/cm3, 2.6%, 0.57 for soil moisture, and 2.62 g/L, -4.5%, 0.51 for salinity concentration, respectively. And MRE and R2 were 9.1%, 0.88 for LAI, and -1.9%, 0.92 for crop yields. These results showed that the distributed agro-hydrological model was able to simulate the soil water flow, salt transport, and crop growth process in JIS with accuracy. The calibrated and validated model was then applied to predict spatial distribution of soil moisture, salinity concentration, crop evaporation and crop yields of the study area in present irrigation water management practices. Effective saturation and salinity concentration in the root zone were chosen to represent soil water and salinity stress on crop growth. Results showed that effective saturation ranged from 0.44 to 0.90 with an average of 0.7 for the JIS. In most areas, soil water could meet crop water consumption needs. In the areas where groundwater depth (GWD) was less than 1.3 m, root water uptake was limited due to waterlogging. The average salinity concentration in the root zone varied from 3.1 g/L in the northwest to 13.5 g/L in the northeast with an average of 6.4 g/L for the whole district. High soil salinity concentration limited crop production seriously. Corresponding to the spatial distribution of salinity concentration in the root zone, crop relative yield (ratio of actual yield and average yield of JIS) ranged from 0.33 to 1.33. The results suggested that for the northeastern part, where GWDs were larger than 2.0 m, more irrigation was needed for leaching salt. It was also better to plant more salt tolerant crops in these areas. In northwestern and southwestern parts, shallow groundwater levels intensified waterlogging or salinity accumulation problems. The study indicated that it is better to keep the groundwater depth not shallower than 1.3 m for maintaining the crop yields.