Study On Precision Irrigation Method Based On Greenhouse Environment Factor And Crop Growth Physiological Information

The greenhouse can fully regulate the light,heat,water and gas resources to develop suitable environment for optimal growth of crops,but the mainstream greenhouses emphasize lighting,heat storage and heat preservation during the design and construction process.Therefore,the high temperature environment is easily formed in the greenhouse,which causes damage to crop growth and seriously affects the utilization efficiency of the greenhouse.Research on scientific and rational precision irrigation methods can promote the development of greenhouse water-saving irrigation,improve crop growth environment,improve greenhouse utilization efficiency,and achieve high-quality and high-yield crops.Research on water-saving irrigation methods is of great significance for promoting sustainable development of agriculture.Aiming at the problem of easy to form a high-temperature environment and crop precision irrigation in summer greenhouses in southern China.In this study,cucumbers with a large planting area were used as research objects,and trials were conducted in the Venlo-type glass greenhouse of Jiangsu University,using soil trough planting.Two kinds of irrigation methods:micro-sprinkler irrigation combined with drip irrigation?MSDI?and surface drip irrigation?SDI?were set up.Observed and contrasted the meteorological factors inside and outside the greenhouse,cucumber plant height stem diameter,sap flow,photosynthetic characteristics and other growth physiological information under two irrigation modes.Through observation comparison and data analysis,the following conclusions are obtained:?1?The temperature and relative humidity of the canopy are basically the same at different heights?0.8,1.3 and 1.8 m?during night.The temperature reached the lowest value around 05:00,reached the highest value around 14:00.Similarly,the relative humidity reached the highest value around 05:00,and reached the lowest value around 14:00.The highest air temperature and the lowest relative humidity all occur at 1.8 m level;the highest relative humidity and the lowest air temperature also occur at 0.8 m level;and,the air temperature and relative humidity levels at height 1.3m appeared to be intermediate between that of the 0.8 and 1.8 m.Relative humidity and temperature change are opposite.After the MSDI irrigation mode was started at different times,the temperature of the canopy between different heights decreased and the relative humidity increased.The temperature ratio is decreasing and the relative humidity is increasing at different heights.The leaf temperature drops by an average of about 4?each time and the duration is about 10 min.About 1 to 2 hours after stopping the micro-sprinkler irrigation,the leaf temperature of the MSDI irrigation mode was restored to the leaf temperature level under the SDI irrigation mode.?2?Before the initiation of micro-sprinkler irrigation of MSDI irrigation mode,and there was no significant difference in plant height and stem diameter of cucumber.After the micro-sprinkler irrigation was started,the plant height growth of the crop was significantly increased by 22.5%?P<0.05?.There was no significant difference in cucumber stem diameter due to the limited growth of cucumber stems.Compared with the SDI irrigation mode,the MSDI irrigation mode has significant differences in single fruit weight and length,which are increased by 13.5%and 2%,respectively.At the same time,the TSS content of cucumber was 24.2%higher than that of SDI irrigation,and had no significant effect on total cucumber yield and transverse diameter.?3?Net radiation and temperature are the main meteorological factors affecting sap flow in plants.The MSDI irrigation mode reduces the sap flow of plants by lowering the temperature and increasing the relative humidity of the air.The stomatal conductance and photosynthetic rate of cucumber leaves increased first and then decreased.The MSDI irrigation mode effectively increased the stomatal conductance and photosynthetic rate of cucumber leaves.The average daily stomatal conductance and photosynthetic rate of cucumber leaves under MSDI mode were higher than SDI mode with 182.8%and 92.4%,respectively.?4?The maximum photosynthetic efficiency of PSII under the two irrigation modes is almost the same,about 0.74⁰.77.The actual photosynthetic efficiency is opposite to the temperature change law.It decreases rapidly with the increase of temperature during the day,reaching the lowest value at about 11:00 noon.The time when MSDI irrigation mode reaches the lowest value lags slightly behind the SDI irrigation mode.The actual photosynthetic efficiency of the leaves under MSDI irrigation mode is significantly higher than that of SDI mode during the daytime.The daily average photosynthetic efficiencies were significantly different between the two irrigation modes,with the values of 0.57 and 0.47,respectively.Air temperature?Ta?,solar radiation?SR?and relative humidity?RH?were the main meteorological factors affecting the photosynthetic efficiency of cucumber.The photosynthetic efficiency was significantly negatively correlated with Ta,SR and RH?P<0.01?.This phenomenon indicates that the use of MSDI irrigation method can alleviate the stress of greenhouse high temperature on the actual light energy efficiency of the PSII and improve the photosynthetic capacity of mesophyll cells.?5?The meteorological conditions in the greenhouse during the growth period of cucumber have the characteristics of high temperature.The average solar radiation in the greenhouse is 121.4 W/m²,and the temperature varies from 19.1 to 32.7? with an average of 26.9?.The average relative humidity in the greenhouse is 66.9%,and the average vapor pressure difference is 0.2 kPa.The range of ET₀ in the greenhouse during the growing period of cucumber was 0.15⁴.41 mm/d,with an average of 2.50mm/d.The range of ET₀ outside the greenhouse during the growing period of cucumber was 0.41⁸.32 mm/d,with an average of 4.09 mm/d.The trend of ET₀changes inside and outside the greenhouse is basically the same,and has a good correlation.The average values of ET_c,ET₀ and E_pan in greenhouse cucumber growth period were 1.71 mm/d,2.46 mm/d and 3.02 mm/d,respectively.ET₀ has a very high correlation with E_pan?R²=0.91?.Through the actual measurement of E_pan,the ET₀ in the greenhouse can be accurately calculated.?6?The greenhouse cucumber crop coefficient was 0.27,0.95 and 0.72 in the early,middle and final growth stages respectively.Crop coefficient based on pan evaporation was 0.24,0.77,and 0.55 at different growth stages.The greenhouse cucumber crop coefficient is less than the recommended value of FAO-56 in the field environment.