摘要：
Long-term prediction of regional groundwater and salt dynamics is important for the agricultural sustainability in Hetao Irrigation District, where the water resources supply and demand contradiction is prominent. The mulched drip irrigation with the well-canal conjunctive irrigation will be applied to save water and control soil salinity. In this study, the improved mass balance model SaltMod by a loosely coupled strategy was used to simulate the long-term groundwater and salt dynamics under current situation and future situation under well-canal conjunctive irrigation with mulched drip irrigation to evaluate the agrucultural sustainability. In the loosely coupled model, 2 SaltMod models were used to simulate the canal-and well- irrigated areas separately. An exchange flux was added in the aquifer mass balance equation to link the canal- and well-irrigated areas. The improved SaltMod could handle with multiple irrigation sources and different groundwater levels in the groundwater aquifer, which makes it possible to be used in the well-canal conjunctive irrigated areas. Then the model was calibrated and validated with 15 years' observation data of the Longsheng well-canal irrigated area in Hetao Irrigation District, Inner Mongolia, China. The data in years between 2002 and 2005 were used as the calibration period and 2006—2016 were used as the validation period. Root mean squared error (RMSE) and relative error (RE) were used to evaluate the results. The results showed that the improved model performed well for calculating the groundwater depth and soil salinity for both canal-and well- irrigated areas. Then the model was used to predict the water flow and soil salinity dynamics in the next 100 years under the current irrigation condition. The results showed that it could sustain a long-term stabilization under the present irrigation practice in the Longsheng well-canal irrigated area. Then the model was applied to simulate the water and salt dynamics with different senarios under the well-canal conjunctive irrigation and the mulched drip irrigation. With the satisfactory result of soil salinity in the canal-irrigated area, the well-irrigated area was the concern, especially the root zone in the well-irrigated area. Different autumn irrigation frequency schemes, irrigation quotas in the crop growing season, groundwater depth in the well irrigation area and groundwater mineralizations were considered to be the impact factors on the soil salinity in the root zone of the well irrigation area. The results showed that, the irrigation quota and groundwater depth had little effects on the variation trend of soil salinity in the root zone of well irrigation area. The autumn irrigation frequency scheme and groundwater mineralization played very important roles on the variation trend of soil salinity. When the autumn irrigation frequency (AIF) was once every two years and the groundwater mineralization increased to 2.0 g/L, the root zone soil salinity would still be less than 3.0 g/kg after 100 years. It would exceed 3.0 g/kg after 60 years when the groundwater mineralization increased to 2.5 g/L. Considering the groundwater mineralization of 90％ well-canal irrigated area was less than 2.0 g/L, we recommended that when exploiting groundwater for irrigation in Hetao Irrigation District, it was necessary to apply the water from Yellow River for autumn irrigation to wash out the soil salt. The autumn irrigation frequency was once every two years and the autumn irrigation quota was 180 mm.%针对内蒙古河套灌区井渠结合的问题,基于SaltMod模型建立井灌区和渠灌区水盐均衡模型,并引入含水层侧向交换量对模型进行改进,利用隆胜井渠结合试验区15 a水盐观测资料对改进的模型进行率定和验证,采用验证后的模型分析了隆胜井渠结合区在现状条件下以及在井渠结合膜下滴灌推广实施后区域的土壤盐分演化规律.结果表明,现状条件下隆胜井渠结合区土壤盐分基本稳定,尤其是渠灌区根系层盐分基本稳定,保持在较低水平,可以在长时期内满足作物生长的需求.当推广井渠结合膜下滴灌后,井灌区的生育期灌溉定额和地下水埋深对其灌溉用地根系层土壤盐分积累的影响较小,而地下水矿化度与秋浇频率的影响较大.对于井灌区,建议采用黄河水2年1次进行秋浇压盐,可以长期将土壤全盐维持在3 g/kg以下,以满足作物生长需求.
