Construction And Evaluation Of Early Warning Algorithm For Facility Lettuce Precision Irrigation

At present,water-saving irrigation methods such as drip irrigation and sprinkler irrigation have been widely used in the production of vegetable facilities,but the phenomenon of frequent irrigation and large irrigation amount still exists.The reason is that the lack of intelligent decision-making methods and forecasting devices corresponding to water-saving irrigation mode is the main reason for the existence of blind irrigation.In order to solve the problem of large irrigation amount and frequent irrigation,a decision algorithm can be constructed to realize accurate irrigation prediction.According to the meteorological information of real-time change in greenhouse,the evaporation of water surface in crop growth environment can be simulated,and then the prediction and calculation of crop water demand information can be realized,so as to provide scientific reference and data support for the irrigation management of crops in greenhouse.Solve the problem of when and how much water is irrigated and how much water is irrigated each time under the condition of facility cultivation.In this experiment,lettuce was used as the test material,and the evaporation of lettuce canopy surface was determined according to EVW20 surface evaporator.Irrigation scheme was developed with accumulated water evaporation(Ep),and 5 test treatments were set.The irrigation coefficient of evaporation dish(Kp)was 0.3,0.5,0.7,0.9 and 1.1,respectively,and the corresponding irrigation amount was 0.3 Ep(I1),0.5 Ep(I2),0.7 Ep(I3)and 0.9Ep(I4),1.1 Ep(I5)to study the early warning algorithm of accurate irrigation of lettuce.The main research results are as follows:(1)Determination of suitable irrigation system based on the evaporation of canopy water:Under the conditions of this test,the yield,biomass and water utilization efficiency of greenhouse lettuce were the highest in the treatment of I3,and the corresponding Kp was 0.72 and 0.85 respectively,Proper amount of irrigation is mainly to ensure that the crop grows under a suitable soil moisture condition,which in addition promotes the plant growth and increases the yield.Therefore,it is concluded that the treatment of 13(0.7Ep)can be used as reasonable irrigation amount under the condition of this test.(2)Determination of water evaporation estimation model based on environmental factors:The determination coefficients of 16 water evaporation models constructed based on environmental factors are Ep16,Ep8,Ep15,Ep11,Ep14,Ep9,Ep10,Ep13,Ep2,Ep7,Ep12,Ep3,Ep6,Ep5,Ep4;The best estimation method is Ep16(Ep16=0.045R+0.926es-1.977),the decision coefficient is 0.849,followed by Ep15(Ep15=0.045r+0.12T-2.320),the decision coefficient is 0.842,and the worst estimation method is Ep5(Ep5=-0.7818ea+3.0942),and the decision coefficient is 0.023.(3)Determination of the model of daily reference evapotranspiration estimation based on water evaporation:Based on the evaporation of water,5 daily reference evtranspiration estimation models were constructed.The determined coefficients R2 of ET1,ET2,ET3,ET4 and ET5 were 0.809,0.798,0.666,0.661,0.851,5different irrigation treatment models were consistent,and the estimated values were highly correlated with the measured values.The consistency index of the model ET5 was 0.93,followed by the consistency index of ET4 was 0.91 and ET3 was 0.88.According to the statistical indexes,the accuracy between treatments in simulated greenhouse lettuce evextranspiration was ET5,ET3,ET4,ET2,ET1.