基于HYDRUS-1D模型的华北低平原区不同微咸水利用模式下土壤水盐运移的模拟

华北低平原区深层地下水的不断超采不仅造成淡水资源的枯竭,还引发了地面沉降、土壤盐渍化等一系列生态环境问题。微咸水在农业上的利用已成为缓解水资源危机的研究重点。为了研究不同咸水灌溉模式的可持续性,本文以华北低平原区的河北省南皮县为例,利用Hydrus-1D模型,基于8种不同微咸水灌溉方案,模拟2008—2013年6年冬小麦-夏玉米轮作制度下,2 m土体水盐通量变化。模拟结果表明,土体剖面盐分积盐区主要集中在下层土壤(100~200 cm);上层土壤(0~100 cm)溶液盐分浓度大部分时间保持在2 g·L~(-1)左右,能保证作物正常生长;但土壤剖面盐分浓度在冬小麦灌浆末期出现峰值且随灌水盐分浓度增加而逐渐升高。土体盐分充分淋洗的关键在于降雨强度,7月份降雨强度是土体脱盐与否的主要影响因素;同时,在丰水年型夏玉米播种后结合出苗水适当灌溉洗盐对土体达到有效脱盐起到重要作用。本文通过综合分析水文年型、土壤剖面盐分的动态分布特征以及结合夏玉米出苗水的洗盐淡水用量3方面因素对土壤盐分迁移的影响,提出华北低平原区两种适宜的微咸水灌溉制度:(1)冬前浇灌小于2 g·L~(-1)的冬小麦越冬水,春后在冬小麦拔节期浇灌一次2~4 g·L~(-1)微咸水;(2)冬前不灌越冬水,春后分别在冬小麦拔节期和灌浆期浇灌2 g·L~(-1)微咸水。两种灌溉制度年均结合夏玉米出苗水的洗盐淡水用量和总耗水量分别为60~70 mm和250~260 mm。本文结果旨在为华北低平原区微咸水利用的节水潜力及其可持续性提供理论指导。

HYDRUS-1D model simulation of soil water and salt movement under various brackish water use schemes in the North China Lowplain

Freshwater resource in the North China Lowplain is nearly been depleted due to continuous overexploitation of deep groundwater resources. This has led to a series of ecological and environmental problems, including land subsidence and soil salinization. The use of brackish water in agriculture to alleviate water crisis in the region has become the new focus of research. In order to determine the sustainability of various irrigation modes of saline water, this study used the Hydrus-1D model to simulate eight different brackish water irrigation schemes in Nanpi County. The model simulated water and salt fluxes in the 0–2 m soil layer in the winter wheat-summer maize crop rotation system for the period of 2008–2013. The simulation results of soil salinity profile distribution showed that the 100–200 cm subsoil layer was the main salt accumulation zone. The upper 0–100 cm soil layer was lower in salt solution concentration with 2 g·L-1 salt solution in most time, which generally ensured normal growth of crops. Soil profile salinity concentration peaked at late winter wheat grain-filling stage. Peak salinity increased with increasing salt concentration of irrigation water. Leaching soil salt in the study area depended mainly on rainfall intensity, especially in July when precipitation was heaviest. Proper leaching of salt after sowing corn in wet years significantly enhanced soil desalination. Based on comprehensive analysis of the effects of three tested factors (hydrological year type, dynamic distribution of soil profile salinity and soil salt migration/leaching), the paper proposed two suitable brackish water irrigation schemes in the North China Lowplain. 1) Pre-winter irrigation of brackish water with less than 2 g·L-1 salt concentration combined irrigation at jointing stage with 2–4 g·L-1 brackish water. 2) Without pre-winter irrigation, wheat was irrigated at jointing and grain-filling stage with 2 g·L-1 brackish water. The amount of freshwater used to leach soil salt at summer seedling stage and the total water consumption of the winter wheat-summer maize system under the above two irrigation schemes were 60–70 mm and 250–260 mm, respectively. This research provided the theoretical basis of water-saving potential through the use of brackish water for sustainable use of the limited water resources in the North China Lowplain.