Study On Water Deficit Diagnosis And Transpiration Estimation Of Summer Maize Under Alternate Furrow Irrigation

Water deficit is the main factor limiting China's agricultural development.In recent years,with the application and promotion of water-saving irrigation technology,the irrigation water use efficiency has been improved.However,whether timely judging crop water deficit is critical to the health of crops,especially the crops has adaptative mechanisms to water stress under water-saving irrigation conditions.Crop water deficit diagnostic indicators derived from deficient irrigation studies may no longer apply.In this paper,the alternate furrow irrigated maize experiment was conducted in water-saving irrigation station of the Northwest A&F University.The conventional furrow irrigation treatment?CFI?,alternate furrow irrigation high water treatment?AFIH?and alternatefurrow irrigation low water treatment?AFIL?treatment were set in the experiment,AFIH and AFIL treatment irrigation volume is2/3 and 1/2 of the CFI treatment irrigation volume respectively.The diagnostic indicators of water deficit in alternate furrow irrigation were studied,and a maize transpiration estimation model was established based on artificial neural network.The main results are as follows:?1?Under alternate irrigation conditions,the maize stem maximum daily shrinkage of AFIH and AFIL treatment was greater than CFI treatment,and the total stem diameter increase of AFIH treatment>CFI treatment>AFIL treatment.In mature stage.The maximum canopy temperature of maize was observed around 14:00 on sunny days,under cloudy weather conditions,the canopy temperature of maize was lower than that in sunny days.Canopy leaf temperature of AFIL treatment and AFIH treatment was greater than air temperature.Canopy leaf temperature of CFI treatment was slightly lower than air temperature.The daily diurnal variation of sap flow rate showed a double-crest curve during sunny days,and there were multi-peak curve during cloudy days.On sunny days,the accumulation of sap flow was significantly greater than that of cloudy days.The highest stem flow was CFI,followed by AFIH and AFIL.?2?The maize stem maximum daily shrinkage?MDS?and daily increase?DI?of different treatments were easily effected by meteorological factors and showed a weak relationship with soil water content,so these indexes could not be directly applied to the diagnosis maize water deficit.The MDS signal value(Signal_MDS,SI_MDS)and DI signal value(Signal DI,SI_DI)can exclude the interference of meteorological factors,it showed a greater correlation between signal value and soil moisture,that can be applied to diagnosis of maize water.During the jointing stage,SI_DI is more suitable as the diagnostic indicator for maize than SI_MDS,and in heading and mature stages,SI_MDS is more suitable than SI_DI for the diagnosis of maize water status.?3?The leaf-air temperature difference?T_c-T_a?reached the minimum value at about 14:00;it could be used as the optimum time to measure leaf-air temperature difference.Under alternate furrow irrigation conditions,the Tc-Ta of AFIH treatment showed a significant correlation with the 30cm depth soil moisture content of the wet side,and Tc-Ta of AFIL treatment showed a significant correlation with the 10cm and 20cm depth soil moisture content of wet side.The critical canopy-air temperature difference at the heading stage of CFI,AFIH and AFIL treatments was-0.27,0.76 and 0.90,respectively.The CWSI empirical model and the theoretical model were established based on the canopy air temperature difference.The optimum observation time of the CWSI empirical model should be around 14:00 in clear weather.The CWSI value of theoretical model can be used to diagnose crop water status at any time between 10:00 to 16:00.Based on the characteristics of alternate furrow irrigation,the irrigation threshold for alternate furrow irrigation was proposed:At jointing and heading stages AFIH CWSI>0.37 and at mature stage CWSI>0.48;at jointing stage AFIL CWSI>0.44;heading and mature stage were CWSI>0.66 and CWSI>0.68,respectively.?4?The response of different treatments to environmental factors was different.Meteorological factors mainly affected stem flow of the AFIH treatment,and soil moisture was main factor affecting stem flow of the AFIL treatment.The influence of water content in different soil layers on stem flow was also different.It was found that the moisture contents of10-20cm and 20-30cm layers were most correlated with maize stem flow.Result of further analysis showed that,for CFI and AFIH treatments,20-30 cm layer soil content was most closely related to sap flow changes.In addition,10-20 cm layer soil content was most closely related to sap flow changes for AFIL treatment.After comparing the R²,RMSE and d-factor values of two models,the ANN model was more stable and accuracy,which was found to be the best model to predict the stem flow.