Research On Micro-spray Irrigation Combined With Drip Irrigation And Its Comprehensive Evaluation

Heat stress in the greenhouse is the main environmental stress faced by plants during their growth,and the poor water use efficiency is a major problem for agricultural irrigation.A rational irrigation mode could improve irrigation water use efficiency and reduce the damage caused by heat stress.This study proposes an irrigation mode of micro-spray irrigation combined with drip irrigation（MSDI）,carried out field experiments in the Venlo-type greenhouse of Jiangsu University with tomato as the test object.The measurement project included environmental factors in the greenhouse,tomato growth and physiological information and evaluated irrigation patterns based on multivariate statistical analysis methods.The feasibility and practicability of MSDI in the greenhouse high-temperature environment are analyzed.Through observation comparison and data analysis,the following conclusions are obtained:（1）The high-intensity photosynthetic effective radiation（PAR）in the greenhouse is always accompanied by high temperature,and the occurrence time of daily maximum photosynthetic effective radiation(PAR_max)overlaps with the maximum ambient temperature(T_max).The ambient temperature（Ta）and relative humidity（RH）in the greenhouse showed a negative correlation trend during the daytime.The MSDI irrigation mode can regulate the Ta and RH through micro-spray,which is manifested as Ta decreasing by 1–2℃and RH rising by 1–3%after the micro-spray is operated,but the effect will not last long.（2）In terms of crop growth,due to the spindling of crops caused by high temperatures,the plant height of tomato plants under the DI in the 2020 season was higher than that of MSDI with the increase in the number of transplanting days.Due to the environmental regulation effect of micro-spray,the stem diameter of tomato plants under MSDI gradually increases bigger than it under DI with the increase of transplanting days.In the 2021 season,the temperature change was from cold to hot,and tomatoes did not show the phenomenon of spindling in two irrigation modes.The plant height and stem diameter of tomato plants under MSDI were better than those under DI.In terms of dry matter mass accumulation,tomatoes’stem and leaf dry matter biomass under MSDI were greater than those under DI.The dry matter biomass of the root was significantly greater than that under DI（P<0.05）.The tomatoes’irrigation water use efficiency（IWUE）did not differ significantly between MSDI and DI.The yield of tomatoes under MSDI was 58.1%higher than that under DI,but the irrigation water consumption of MSDI was 60.6%more than DI.There was no significant difference（P>0.05）between tomato fruit’s soluble solids content and fruit shape index under the two irrigation modes.Still,the fruit shape standard of tomato fruit under MSDI was significantly（P<0.05）better than that under DI.（3）The changing trend of PAR and leaf temperature（Tl）in the greenhouse during daytime is to rise first and then decrease,and the effective quantum yield of PSII（ФPSII）of tomatoes shows the opposite trend of PAR.The increase and decrease of Tl will also causeФPSII to change in the opposite law.Using a rapid light curve,it was found thatФPSII under MSDI was higher than under DI.MSDI can effectively reduce Tl in high-temperature weather through micro-spray.The cooling range is 3–6℃,which is more effective than the adjustment effect of Ta and makes the Tl continue to be lower than that under DI during the period when micro-spray is operated.（4）The physiological state of tomatoes under MSDI is more stable than that under DI.Comparing the improvement rate ofФPSII of MSDI in two seasons,it is found that Tl is the main factor affecting the improvement rate ofФPSII.When the leaf temperature is below 35℃,the improvement rate ofФPSII of MSDI is relatively obvious;when the leaf temperature exceeds35℃,the improvement rate ofФPSII is significantly reduced.Due to the fixed time and length of micro-spray,there are differences in the cooling effect of different periods.When the temperature reaches the highest level of the day at noon,the effect of short-term（1 minute）micro-spray is relatively weak.（5）By applying principal component analysis on nine variables,including yield（X1）,IWUE（X2）,and single fruit weight（X3）.Two principal components were extracted:comprehensive growth level and economic benefit.Tomato plants under MSDI were better than DI in terms of comprehensive growth level;in terms of economic benefits,tomato plants in the two irrigation modes showed similar levels.MSDI has a lower IWUE because the amount of irrigation has increased compared to the DI,which affects the economic benefits.Combining the scores and rankings on the two principal components,the MSDI irrigation model performed better than the DI.（6）By conducting path analysis,exploring the degree of influence of four environmental factors of PAR,Tl,Ta and RH on theФPSII of tomato plants under a high-temperature environment,it was found that the environmental factors with the greatest impact onФPSII is PAR,followed by Tl and Ta,all these three factors have different degrees of negative impact onФPSII.Still,relative humidity shows a positive effect onФPSII.MSDI can achieve the environmental control effect of cooling and humidification,thereby improving the photosynthetic ability of tomato plants in high-temperature environments.Based on the two multivariate statistical analysis methods,the MSDI irrigation mode is more suitable for greenhouse cultivation in high-temperature environments than the DI.MSDI can improve the crop growth environment in the greenhouse,improve the growth indicators and physiological indicators of crops,and maintain great IWEU,a scientific and effective irrigation mode.