干旱区滴灌棉田灌水量与灌溉周期关系

Relationships Among Drip Irrigation Amount, Irrigation Interval and Deep Percolation:A Case Study on Manas River Oasis, Xinjiang

由于其节水增产的优势,近年来,膜下滴灌在我国西北干旱区绿洲农田得到了迅速推广。由于轮灌仍是目前农田用水分配的主要方式,并且还需要考虑滴灌产生的土壤盐分积累问题,因此,对滴灌灌水量(Q)、灌水周期(T)以及相应的深层下渗(L)关系研究,不仅是农田用水分配的要求,也是盐分控制的需要。本文利用田间试验数据校验HYDRUS-2D模型,进行数值模拟试验,并结合马尔可夫链模型分析,分析不确定蒸散下的Q-T-L关系,结果显示:①总体上,随着灌水量的增加,可支持的灌溉周期增加,同时深层下渗增加,Q-T-L关系曲线表现为非线性关系;②其中存在3个关键Q-T阈值点:深层下渗出现点(Q为35mm,T为5d)、灌溉周期增加减缓点(Q为65mm,T为10d)、最大灌溉周期点(T为11d,Q为120mm)。因此,①在以水分利用为优先的模式下,最大灌水量不应超出35mm,最大灌溉周期为5d;②在灌溉间隔时间优先的模式下,有最大灌水周期11d,所需灌水量为120mm,适宜的灌水周期为10d,所需灌水量为65mm;③在有盐分淋洗需求模式下,适宜的灌水周期为10d,所需灌水量为65mm,产生下渗量约占灌水量17%,可用于根区盐分淋洗;④潜水位对灌溉产生作用的阈值深度是-300cm,高于时潜水可以补给根区土壤水分,从而增加灌溉周期。利用本文数值模拟与方法,可以为不同气候与土壤情形区域农田滴灌灌溉设计提供指导。

Drip irrigation has been developing rapidly in Xinjiang in the last two decades because of its high water use efficiency. However, salinity accumulation caused by drip irrigation is an important issue to be considered in irrigation management. The amount of proper irrigation water （Q）, irrigation interval （T）, and deep percolation （L） are fundamentals of efficient drip irrigation management and soil salinity control. Revelation of the complicated relationships among them through field experiment is both time consuming and costly. In this paper, a Q-T-L relationship was derived through combining numerical simulations of drip irrigation with HYDRUS-2D model and field experiments in the Manas River oasis of Xinjiang. And the relationship can be used as a guide for irrigation practice. During the simulation, uncertainty of predicting crop evapotranspiration was simulated by the Markov chain approach.The Q-T-L curves present general, non-linear relationships among irrigation water amount, irrigation interval and deep percolation. The irrigation interval increases with Q in each irrigation application, and percolation increases with irrigation water amount. Three important threshold points on the curve should be noted： deep percolation occurs when the amount of irrigation water exceeds 35 mm in depth in 5 days intervals; when the amount of water exceeds 65 mm per irrigation, the irrigation interval increase slows down while deep percolation speeds up; Irrigation intervals are not supposed to exceed 12 days because of the amount water being irrigated and the significant percolation. From these threshold points, we can conclude the guideline of irrigation methods. With water use efficiency as the first priority, irrigation water amount should be no more than 35 mm with an irrigation interval of less than 5 days. With a longer irrigation interval as a priority, irrigation water amount should be no more than 120 mm and the irrigation interval should be less than 11 days. An optimum combination of irrigation water amount of 65 mm and interval of 10 days and mean percolation rate of 17% is important for salt leaching while maintaining a relatively high water use efficiency. The depth of 300cm is an important threshold point of groundwater table. Irrigation intervals can be extended for the replenishment of soil water in root zone which comes from groundwater when the groundwater table exceeds 300cm.