Study On Cucumber Water Consumption Model And Efficient Irrigation Index Of Greenhouse Conditions

Studying crop evapotranspiration and determining appropriate irrigation schedule is of great significance for achieving efficient use of agricultural water,promoting high yields and quality of facility crops,and improving farmers'living standards.In this paper,greenhouse cucumber cultivar planted during 2017?autumn-winter planting season?and 2018?spring-summer planting season?in the Venlo-type greenhouse of Modern Agricultural Equipment and Technology of Jiangsu University was used as the test crop.The effects of different water treatments on the physiological and ecological indexes,yield and water use efficiency?WUE?of greenhouse cucumber under drip irrigation were studied.The irrigation method was to design three irrigation levels based on the cumulative water surface evaporation of 20 cm standard pan,the coefficients of evaporating pan for different growing stages of cucumber plants and water treatments were set differently.The systematic field observation,research and analysis on soil moisture status,physiological and ecological indicators,crop water consumption,yield and WUE of greenhouse cucumber under different water treatments were conducted.Based on the regression analysis of greenhouse cucumber ET_c and measured meteorological data in greenhouse,an empirical model for estimating greenhouse cucumber ET_c using conventional meteorological data was proposed.In order to estimate the transpiration?T_r?of greenhouse cucumber and evaporation beneath the canopy in greenhouses,this study modified basic crop coefficient(K_cb)as well as soil evaporation coefficient?K_e?based on the Modified Dual Crop Coefficient model recommended by FAO-56 through the application of measured meteorological data,leaf area index?LAI?and soil moisture content in the greenhouse.The greenhouse reference crop evapotranspiration?ET₀?was determined by FAO-56 modified Penman-Monteith?P-M?model,hence,the greenhouse cucumber ET_c and T_r were estimated.By measuring the growth status of cucumber plants in different planting seasons?spring-summer,autumn-winter?,the ET_c and T_r by lysimeter and stem flow meter in a Venlo-type greenhouse,the Modified Dual Crop Coefficient model predictions were validated.The research results obtained are as follows:1)The effects of different water treatments on growth index during the whole growing period of greenhouse cucumber plants were analyzed,and results indicated that the plant height,stem diameter and LAI of greenhouse cucumber were significantly correlated with soil water content under different water treatments.The plant height and stem diameter of the three water treatments?T1,T2 and T3?reached the maximum at the late stage of crop growth.The plant height of spring-summer cucumber for T1,T2 and T3 were 247,206 and 147 cm,respectively,and were 215,189and 168 cm in autumn-winter planting season,respectively.The spring-summer cucumber stem diameters for T1,T2 and T3 were 10.10,9.09 and 8.41 mm;and 8.13,7.39 and 6.45 mm in autumn-winter planting season,respectively.LAI reached the maximum in the middle of crop growth.corresponding values for treatments T1,T2 and T3 were 5.12,3.77 and 2.64 in spring-summer planting season;and 4.66,3.73 and 3.13 in autumn-winter planting season,respectively.The results showed that the cucumber plant height,stem diameter and LAI increased with the increase in soil water content.2)By analyzing the effects of different water treatments?T1,T2 and T3?on stem flow rate,photosynthetic rate and stomatal conductance of greenhouse cucumber at different growing stages,it was further confirmed that water deficit in any growth stage of cucumber reduced the stem flow rate,photosynthetic rate and stomatal conductance,which in turn affected the operation and accumulation of dry matter in cucumber plants.Through the observation of stem flow rate of cucumber plants under different weather conditions,it can be concluded that solar radiation is the main factor affecting the change of stem flow,this change is always influenced by solar radiation fluctuations.3)The effects of different water treatments on greenhouse cucumber yield,ET_c and WUE in different growing seasons were studied,The results showed that with the decrease of soil water content,greenhouse cucumber yield and WUE followed a decreasing trend,and different degrees of water deficit had certain inhibitory effects on ET_c at different growth stages.Furthermore,the average fruit weight,fruit stem,fruit length and number of fruit per plant decreased with the decrease of soil water content,while the proportion of cucumber fruit malformation increased with the increase of water deficit in different growth stages.4)Combined with the measured meteorological data in the greenhouse,the regression analysis was carried out using meteorological factors such as solar net radiation and measured daily ET_c during the growth period of cucumber.Results indicated that the net radiation and the daily minimum relative humidity are the main meteorological factors affecting the crop ET_c;This indicate that,in the absence of complete meteorological data,an empirical model established by the net radiation and daily minimum relative humidity can be used to estimate ET_c.5)The Modified Dual Crop Coefficient model was used to estimate the greenhouse cucumbers ET_c and T_r and good agreements with the measured values were obtained.The daily estimated and measured ET_c by the Modified Dual Crop Coefficient model during the whole growing period of greenhouse cucumber in spring-summer were 3.05 and 2.94 mm·d^-1,and the estimated and measured values of ET_c during the whole growth period of greenhouse cucumber in autumn-winter were 2.53 and 2.76 mm·d^-1,respectively.The daily estimated and measured T_r values by the Modified Dual Crop Coefficient model for spring-summer season were 2.37 and2.19 mm·d^-1,and the daily average estimated and measured T_r values by the Modified Dual Crop Coefficient model for autumn-winter season were 1.43 and 1.34 mm·d^-1,respectively.The results also showed that the average daily T_r of ET_c in the whole growth period of greenhouse cucumbers in different growing seasons were 64.62%?spring-summer planting season?and 60.59%?autumn-winter planting season?.The research results not only provide a theoretical basis for the development of accurate greenhouse cucumber irrigation schedule,but also have important significance for achieving intelligent control of greenhouse environment and reducing soil evaporation in greenhouses.