河套灌区种植结构变化对农田系统水量平衡的影响

种植结构调整是灌区农业节水的重要措施。1990年以来,河套灌区种植结构发生了剧烈变化,小麦等粮食作物种植面积大幅减小,葵花等经济作物种植面积大幅增加,对灌区水循环系统带来显著影响。针对这一问题,系统解析了灌区种植结构变化对农田系统的影响机制,采用阿维里扬诺夫经验公式、修正的Penman公式(1948)、Penman-Monteith公式(1973)等分别计算了河套灌区1990—2013年潜水蒸发量、蒸散耗水量等各水量平衡要素的变化情况,并从多个时间尺度分析了种植结构的变化对灌区农田系统水量平衡要素的影响。结果表明,1种植结构变化对垂向水量平衡要素蒸发耗水量和潜水蒸发量影响最为显著,其通量值明显减小;其次是对灌溉水量和田间入渗量的影响;对水平向水量平衡要素地表排水量影响最小。2潜水蒸发量、蒸发耗水量、灌溉用水量和田间入渗量在丰、平、枯3种典型年均呈不同程度的减小趋势,而地表排水量在不同水平年变化差异较大。3月尺度上,5月灌溉水量和6月潜水蒸发量与经济作物种植比例增加显著相关。4农田系统总输入水量与总输出水量总体呈下降趋势,水循环通量减小,水循环强度减弱。1990—2005年水分蓄变量整体呈现负平衡的状态,2006—2013年土壤层水分蓄变量为正,但由于实际土壤层增厚、土壤含水率仍然呈下降趋势。

Effects of the Planting Structure Adjustment on Water Budget of Field System in Hetao Irrigation Area

The adjustment of local planting structure is an important measure of agricultural water-saving in an irrigation area.Since 1990 the planting structure in Hetao irrigation area has changed dramatically,the planting ar ea of wheat and other food crops have drastically reduced,while the planting area of sunflower and other cash crops have sharply increased.This great change has brought significant impacts on water cycle system in irriga tion area.Based on the processes of water cycle system,the influencing mechanism behind the effects of the planting structure adjustment on the field system and water budget elements in Hetao irrigation area on multiple time scales were analyzed.The change of phreatic evaporation,water consumption of evaporation and other wa ter budget elements from 1990 to 2013 were calculated by using Aver'yanov's formula,modified Penman formula(1948),and Penman-Monteith formula(1973).The results showed that,①the water consumption of evaporation and the phreatic evaporation,these two vertical water balance elements were greatly influenced by the changing planting structure,and their flux values reduced remarkably.Furthermore,the influences on irrigation water and infiltration water were weaker.As for horizontal water balance element,the influence on surface displacement was the weakest.②Whether in high flow,low flow or normal years,phreatic evaporation,water consumption of evaporation,irrigation water and infiltration water decreased at the different degrees,while surface displacement performed differently on different typical years.③On monthly scale,irrigation water in May and phreatic evapo ration in June had strong relationships with the increasing cash crops.④Both of the total input and output water in field system descended,meanwhile the flux and intensity of water cycle reduced.Water storage was in a nega tive balance state during 1990-2005.During 2006-2013,water storage was in a positive balance state,nevertheless,the soil moisture was still falling,which resulted from thickness in soil layer.