Research On Unconventional Water Utilization And Irrigation Optimization In Facility Agriculture

In recent years,with the rapid development of facility agriculture,the contradiction between high agricultural water demand and water shortage has become more prominent.The rainwater catchment project is an effective way to solve the contradiction between agricultural water supply and demand.Therefore,the research on the application of rainwater catchment project in facility agricultural irrigation is of great significance to agricultural water saving,efficient use of rainfall resources and modern agricultural development.This paper focused on the surface runoff and rain collection,greenhouse tomato irrigation system optimization and reservoir volume optimization with the example of the facility agricultural community located in Wuqing,Tianjin.The main research work and results were as follows:(1)According to the actual hydrometeorological data of the study area,an integrated hydrology model(GA-HYDRUS model)was developed based on improved Green-Ampt model and HYDRUS model.The results showed that the NSE values of the average soil moisture content were above 0.5,and the R~2 were greater than 0.9.Thus it was reasonable and effective in this area.The average rainfall collection rate in the rain collection test area was 30%,and the loss rate along the way was 70%.The greater the rainfall,the higher the rainfall volume and the rainfall collection rate.In addition,the high rainfall intensity and concentrated rainfall characteristics were more conducive to rainwater collection.In short,the rainwater collection potential is huge in the study area.(2)The improved P-M formula was used to calculate the reference crop evapotranspiration.Refer to the greenhouse tomato data,an Aqua Crop model was established to estimate the crop water demand and optimize the irrigation plan.The simulation indicated that the total water demand of greenhouse tomatoes was 212.6mm,and the water demand increased first and then decreased,which was the largest during the flowering and fruit setting period.The results of the six simulated irrigation schemes showed that the greater the irrigation amount,the higher the yield.However,the crop water use efficiency and irrigation use efficiency were decreased.Finally,the optimal irrigation plan was determined to be 160mm(75%ET)total irrigation and 10mm per irrigation.(3)A correlation map of rainfall and runoff was made to estimate the monthly surface flow and collectable rainfall of the permeable surface during the rainy,normal and drought years in the study area.Three schemes were formulated according to the conditions of rainwater harvesting and irrigation.The reliability indexs and benefit-cost ratio of each scheme increased as the volume of the reservoir increased.When the volume of the reservoir reached the optimal volume,the replacement rate of groundwater and water supply guarantee rate became the fixed values,but the benefit-cost ratio began to decrease.The benefit-cost ratio of existing projects is less than 1,which needs improvement.The optimal reservoir volumes of the three schemes were determined to be 390m~3,1230m~3,and 1140m~3.Exploring new water resources and saving water is an effective way for facility agriculture to increase the rate of collected rainwater,save groundwater resources and meet irrigation needs.Increasing the collection rate of the rainwater collection could improve economic efficiency and reduce the volume of the reservoir while ensuring the groundwater replacement and water supply guarantee rate.Exploiting the rainwater harvesting potential is the future development direction of facility agriculture in the study area to use rainfall resources efficiently.