用有理设计方法优选地表滴灌滴头流量合理性分析

针对地表滴灌单个滴头下土壤水分入渗过程中地表湿润半径r和垂直入渗深度h的随时间变化问题,采用室内土柱试验方法和有理设计方法,运用试验数据对r和h与入渗时间T的幂函数方程进行参数估算,并检验参数间相互约束条件。以粉砂壤土为试验材料,试验研究不同土壤容重(1.3、1.4、1.5 g/cm~3)和滴头流量(1、2、4、8 L/h)条件下,单个滴头灌水时r及h随时间变化的规律。结果表明:1)随着土壤容重的增大,土壤饱和容积含水量降低,r几乎没有变化,垂直入渗深度h减小;2)采用有理设计方法对入渗参数A、B及幂指数C、D进行估算并检验,参数间满足相互约束条件,误差较小,表明可以根据参数A、B、C、D估算值,及r和h与入渗时间T的幂函数方程,计算r和h随时间的推进过程;3)给定灌水量2 L时,滴头流量为1 L/h,垂直入渗深度较大,用有理设计方法计算表明一次灌水持续时间较长,不能满足田间轮灌的要求,且易产生深层渗漏;滴头流量为8 L/h时,地表湿润半径过大,滴头附近地表产生积水。粉砂壤土采用滴灌时,4种滴头流量里,滴头流量为2～4 L/h时最为适宜。用有理设计方法计算r和h为滴灌系统优化设计提供了理论参考。

Rationality analysis based on a rational design method of emitter discharge optimization

Aiming at problems of the changes the surface wetting radius (r) and the vertical infiltration depth (h) with time under single dripper in surface drip irrigation,a indoor soil column method and rational design method were conducted.The parameters in the power function equation of r,h and infiltration time (T) were estimated based on experimental data,and the mutual constraints among these parameters were tested.In the study,a series of infiltration experiments were conducted with silt loam,including three soil bulk densities (1.3,1.4 and 1.5 g/cm³),and four dripper discharge (1,2,4 and 8 L/h).The changing processes with time of wetting radius (r) and the vertical infiltration depth (h) under single dripper irrigation were recorded.The results showed that:1) The saturated soil water content and h decreased with the increasing of the soil bulk density,while the soil bulk density showed little effect on r.2) The infiltration parameters (A,B) and power exponent (C,D) were estimated and tested by the rational design method,the mutual constraint conditions were satisfied among the parameters,and the error was small.It indicated that the changing process of r and h could be calculated based on the power function and the parameters (A, B,C,D).3) For a given irrigation amount of 2 L,the vertical infiltration depth was relatively deeper when the dripper discharge was 1 L/h,which could easily resulted in deep percolation.Meanwhile,the duration of one irrigation calculated by rational design method was relatively longer,and it met the requirements of field rotation irrigation;The surface wetting radius was relatively larger when the dripper discharge was 8 L/h,resulting in surface water accumulation near the dripper.In conclusion,the flow rates of 2 and 4 L/h were more suitable for the drip irrigation under silt loam soil condition.This study indicated that the rational design method could be used as a tool for optimal design of drip irrigation system.