微咸水膜下滴灌棉田漫灌洗盐评价

Evaluation of soil salts leaching in cotton field after mulched drip irrigation with brackish water by freshwater flooding

合理利用微咸水灌溉对缓解淡水紧缺有重要意义。为评价漫灌对微咸水膜下滴灌棉田地表以下0～60 cm深度积盐的淋洗效应,2013年漫灌前、后采用EM38-MK2型电磁感应仪进行大地表观电导率（ECa）调查,通过取样率定得出对应盐分解译模型。将解译获得的漫灌前、后土壤含盐率作为区域化变量,经K-S检验为正态分布,并分别服从指数和球状半方差函数模型。变程相近而基台值远大于灌前,表明灌后变异程度增强。Kriging插值结果显示,实际不合理的漫灌方式,使得灌后土壤返盐,0～60 cm深度范围积盐增量达4.1×104kg/hm2。利用HYDRUS-1D建立土壤水盐运移模型模拟优化的灌水定额为360 mm,较实际灌水定额615 mm节水255 mm,脱盐率为39.3%。持续微咸水灌溉需要完善的农田排水、排盐渠系和盐分排泄区。

Rational use of waters with elevated salinity is likely one option to meet the increased demands of freshwater. A cotton field in southern Xinjiang which was irrigated with brackish water by drip irrigation during the growing season,was subjected to flood irrigation with freshwater after harvest to leach the accumulated salts in the about（0 ～ 60）cm soil zone. To evaluate the efficiency of the flood irrigation,electromagnetic induction EM38-MK2 was applied to measure the apparent soil electrical conductivity（ECa） before and after the flood irrigation in April 2013. Two sets of samples were collected to calibrate the measured ECa. The first set of samples which were collected before the application of irrigation to the field consisted of twenty samples while the second set consisted of twenty-four samples and these were also collected after the irrigation. The optimal semi-variance models of before and after the flood irrigation with the approximate range variations were exponential and spherical models,respectively. The still（C0＋C） result obtained after implementing the flood irrigation was much higher than that before the irrigation. Thus,variation of soil salinity was enhanced after the flood irrigation. The spatial distribution of field salinity was inter-polated by Kriging method. The inappropriate flood irrigation regime resulted in accumulating soil salts rather than leaching salts for the depth of 0～60 cm. The soil salts increased by 41×103kg/hm2 after the flood irrigation. Compared to the applied amount of 615 mm,the optimum irrigation regime calculated by the HY-DRUS-1D software may save 255 mm of freshwater and leach 39.3% of the soil salts. Sustainable irrigation with brackish water requires that suitable drainage canals and places are made available.