微润灌溉变工作水头调控下土壤水分运移及湿润体胀缩机理研究

Study on the Mechanism of Soil Moisture Transport and Wet Body Expansion and Contraction Under the Control of Variable Working Water Head in Moistube Irrigation

为研究动态工况条件下微润灌供水动态变化、土壤水分运移及含水率重分布特征、湿润锋膨缩特性等机理,以室内模拟试验实测含水率、湿润锋面积、微润管出流量数据为依据,探索恒定水头和变水头条件下微润灌土壤水分运动规律,并基于试验实测数据对恒定水头下微润灌湿润锋推移模型进行了修正,提出了基于通量平衡共轭的微润灌水头调增湿润峰运移距离预测模型。结果表明:①恒定水头条件下微润灌累积入渗量随着时间线性增长,入渗速率、累积入渗量与压力水头显著正相关。当调增-调减水头时微润灌入渗速率、累积入渗曲线增长趋势均有显著变化。水头从1 m调增到2 m时,相同时段内累积入渗量和入渗速率分别增加到调增水头前的1.63倍、1.51倍。水头从2 m调减到1 m时,相同时段内累积入渗量和入渗速率分别减少到调减水头前的33.7%、38.63%。调增-调减水头变量越大,该趋势愈发显著。随着时间推移累积入渗量增长趋势、入渗速率均趋于稳定。②当调增工作水头时湿润锋运移速率、湿润体平均含水率显著增大。调减工作水头时湿润锋运移速率显著变小,湿润体平均含水率缓慢增大,随着时间推移湿润锋运移速率、湿润体平均含水率均趋于稳定状态。水头从1 m调增到2 m时,调增水头后72 h内湿润锋面积增加到调增水头时刻湿润锋面积的2.92倍。水头从2 m调减到1 m时,调减水头后72 h内湿润锋面积增加到调减水头时刻湿润锋面积的1.57倍。③构建了微润灌水头调增湿润锋运移预测模型,采用模型评价优度指标分析可知,湿润锋运移距离实测值和模拟值吻合较好,MRE和NRMSE值均接近于0.022,NSE的值均大于0.890,证实了模型优度及较好适用性。研究结果证实了可通过即时调节微润灌溉工作水头,从而人为调控微润管出流、入渗特征及含水率分布的可行性。在实践应用方面,可基于变水头下微润灌湿润体的情景模拟结果和典型设施作物根系需水规律,拟定出不同设施作物适宜的微润灌技术参数范围和灌溉模式。

In order to study the dynamic changes of water supply for moistube irrigation,soil moisture migration and redistribution characteristics of water content,and the expansion and contraction characteristics of wetting front under dynamic working conditions,the water content,wetting front area,and moistube pipe outflow were measured by laboratory simulation experiments.Based on the data,the movement law of soil moisture under constant water head and variable water head conditions was explored,and based on the experimental data,the wetting front transition model of wetting irrigation under constant water head was revised,and a flux-equilibrium conjugate-based microfluidic model was proposed.A model for predicting the migration distance of moist peaks was proposed by adjusting the irrigation head.The result showed that:①Under the condition of constant water head,the cumulative infiltration volume of moistube irrigation increased linearly with time,and the infiltration rate and cumulative infiltration volume were positively correlated with the pressure water head.The infiltration rate and cumulative infiltration curve growth trend of moistube irrigation changed significantly with the regulation of increasing or decreasing water head.When the water head was increased from 1 meter to 2 meters,the cumulative infiltration volume and infiltration rate increased to 1.63 times and 1.51 times,respectively,of that before the adjustment of the water head.When the water head was reduced from 2 meters to 1 meter,the cumulative infiltration volume and infiltration rate in the same time period were reduced to 33.7%and 38.63%of those before the head adjustment,respectively.The larger the variable of increasing-adjusting head,the more pronounced this trend.With the passage of time,the growth trend of the cumulative infiltration amount and the infiltration rate tended to be stable.②When the working water head was increased,the wetting front migration rate and the average moisture content of the wetting body increased significantly.When the working head was reduced,the wetting front migration rate was significantly reduced,the average moisture content of the wet body increased slowly,The migration rate of the wetting front and the average moisture content of the wetting body tended to be stable with time.When the water head increased from 1 meter to 2 meters,the area of the wet front increased to 2.92 times within 72 h of that when the water head was adjusted.When the water head was reduced from 2 meters to 1 meter,the area of wet front increases to 1.57 times of that at the moment of water head reduction within 72 h.③The prediction model of moist front migration was constructed by using the model evaluation goodness index analysis.It can be seen that the measured value of moist front migration distance was in good agreement with the simulated value,the MRE and NRMSE values were close to 0.022,and the NSE values were all greater than 0.890,which confirmed the goodness and good applicability of the model.The results confirm that it is feasible to artificially regulate the outflow,infiltration characteristics and water content distribution of the micro-moistening pipe by adjusting the working head of moistube irrigation.In terms of practical application,the appropriate technical parameter range and irrigation mode of different facility crops can be worked out based on the scenario simulation results of wet-body of moistube irrigation under variable water head and the water requirement law of typical facility crops'roots.