Research On Typical Crops Of Economic Irrigation Lower Limit For Drip Irrigation In Greenhouse

The crops studied in this paper are tomatoes("Shengmei"),cucumber("Jinyun 401")and eggplant("Angela"),which require large amounts of water and have high market demand.The experiment was conducted from April 2018 to December 2018 in the Agricultural Demonstration Park of Northland Spring,Wuqing District,Tianjin.The test plots of the three crops were treated with 100% and 50% irrigation,and the response of crop yield to different water treatments was studied.The water balance method was used to simulate the dynamic change of soil moisture content under drip irrigation under plastic mulch in greenhouse.Taking the minimum to the quadratic sum of the difference between simulated and measured value of the soil moisture content as the target,the crop coefficient parameters are calibration to determine the crop coefficient,and the crop water requirement is determined by the crop coefficient method.The actual dry matter accumulation process of the crops is determined by the method of fixed plant test,The temperature stress index?water stress index and dry matter conversion factor of the crop growth model parameters are determined by minimize the quadratic sum of the difference between simulated and measured value of the dry matter weight.Then combine the crop water requirement with the crop growth model,taking the maximum economic benefit per unit area as the goal,the economic irrigation schedule of crop was analyzed and determined.The soil moisture content before each irrigation in the economic irrigation schedule is taken as the crop's economic irrigation lower limit.The main findings obtained are as follows:(1)The dry matter weight of cucumber,eggplant and tomato stems,leaves and fruits during growth period was measuring under drip irrigation under plastic film in greenhouse.The cumulative dry matter weight of fruits of three crops increased with the increase of days after planting,and showed a "S" growth pattern.The changes of cumulative dry matter weight of stems and leaves were relatively small,and the dry matter weight of leaves showed a downward trend in the later growth period.(2)The response of crop yield to different water treatments was obtained.In the early stage of crop planting,there was no significant difference in crop yield under different water treatments.At the peak of fruit stage,crop yield under two irrigation treatments began to differentiate obviously.Under the current year's test,the 100% irrigation treatment is significantly higher than the 50% irrigation treatment.For tomatoes,the value is 11.43%;for eggplant,the value is 28.54%;for cucumber,the value is 29.84%.(3)The growth model parameters of cucumber,eggplant and tomato under different irrigation treatments were calibrated using the first round of experimental data.The applicability of the model parameters is analyzed with the second round test data,and the results show that the applicability is good.(4)Based on the dynamic simulation model of soil moisture content and crop growth model,the economic irrigation schedule of three crops and their corresponding economic irrigation lower limit was obtained.Based on the analysis of two rounds of experiments,it can be concluded that the economic irrigation lower limit of three crops does not change with the growth time,and its value is a constant.The economic irrigation lower limit of tomato was 0.2338,accounting for 80.62% of field water capacity;the economic irrigation lower limit of eggplant was 0.2292,accounting for 79.03% of field water capacity;and the economic irrigation lower limit of cucumber was 0.2340,accounting for 80.68% of field water capacity.(5)The effect of water saving and income increasing of crops under economic irrigation schedule was obtained.Compared with the current irrigation system,the economic irrigation schedule has obvious benefits of saving water,increasing yield and increasing income.Based on the analysis of two rounds of experiments,it can be concluded that: the irrigation amount of tomato reduced by 21.43%,the yield increased by 3.34%,the benefit increased by 3.75%,the irrigation amount of eggplant reduced by 26.32%,the yield increased by 1.18%,the benefit increased by 1.73%,the irrigation amount of cucumber reduced by 22.06%,the yield increased by 13.76%,and the benefit increased by 14.76%.