| The crop water stress index(CWSI)is an effective index to reflect crop water stress by using the difference between crop canopy and atmospheric temperature("canopy-air temperature difference").It is the great significance to realize non-destructive real-time monitoring of crop moisture status and guide precise irrigation,to quantitative research on the relationship between canopy-air temperature difference and soil,plants and atmosphere,to established the crop of moisture monitoring and diagnosis model based on CWSI.In this study,two winter wheat varieties Xindong43 and Xindong22 in northern XinJiang were used as test materials,and the non-destructive monitoring test of water status of drip irrigation wheat was carried out continuously for 4 years.Based on the quantitative analysis of the correlation between canopy-air temperature differences and farmland meteorological factors,water status and crop growth,constructed the CWSI diagnostic and predictive model on drip irrigation of winter wheat based on canopy-air temperature differences,the aim is to provide a theoretical basis for accurate management of winter wheat moisture by drip irrigation in northern XinJiang.The main results are as follows:(1)The optimal time for monitoring canopy temperature of drip irrigation of wheat for multiple days or a day was between 13:00 and 15:00(Beijing time,the same below).When the irrigation quota of winter wheat under drip irrigation was less than 35mm,the difference between canopy temperature and canopy-air temperature showed a certain degree of response to water stress in the heading and flowering stage,but it could be recovered after rewater,in the grain filling stage could not meet the water demand of wheat.The canopy-air temperature difference and canopy temperature continues to rise and does not recover after rewater and the water stress was aggravated.Drip irrigation of winter wheat will not be subject to water stress when the irrigation quota is greater than 56mm after returning to green.(2)There was a significant negative correlation between canopy-air temperature differences and canopy leaves water content,plant water content and canopy equivalent water thickness(P<0.05).Canopy-air temperature difference can better predict canopy leaves water content,plant water content and canopy equivalent water thickness.The fitting result is the best one day before irrigation,followed by the cumulative result of three days before irrigation.Results of model test on canopy-air temperature difference and canopy leaves water content and plant water content in the whole growth period at the day before irrigation:MAE was 5.25 and 4.26,RMSE was 6.57 and 5.24,COC was 0.94 and 0.94.Test results of fitting equation for jointing period of equivalent canopy water thickness,the MAE was 0.034,RMSE was 0.04,COC was 0.91,after the jointing stage the MAE was 0.16,RMSE was 0.2and COC was 0.95.(3)The canopy-air temperature difference on the day before and the day after irrigation could well reflect the change of soil water potential of 0-60cm,but the canopy-air temperature difference before and after irrigation and the accumulated temperature difference of the three days before irrigation could not reflect the change of soil water potential.The correlation between this site and the canopy-air temperature difference reached an extremely significant level between the day before and the day after irrigation(P<0.01).The correlation coefficients were 0.882 and 0.812 respectively,and the fitting effect of the day before irrigation is better than that the day after irrigation.Therefore,below the drip irrigation belt of 40-60cm is the best monitoring site for soil water potential.(4)The influence of meteorological factors on canopy temperature is:atmospheric temperature>solar radiation>relative humidity>wind speed.The result of fitting the canopy temperature in different growth stages is optimal.The fitting equations of canopy temperature and meteorological factors from jointing to heading stage and grouting stage were as follows:Tc=0.804Ta-0.012RH+3.454W+0.03Ra-2.371?Tc=1.022Ta+0.213RH-1.072W+0.016Ra-7.598.The correlation coefficients were 0.804 and 0.724 respectively.Fitting equation of inspection results MAE was 1.06 and 2.71,RMSE was 1.23 and 2.8,COC was 0.804 and 0.91.It showed that the canopy temperature model based on meteorological factors has better estimation accuracy.(5)The canopy-air temperature difference under 525mm~600mm irrigation quota could better reflect the changes of net photosynthetic rate(Pn),stomatal conductance(Cond),transpiration rate(Tr),intercellular carbon dioxide concentration(Ci)and leaf water potential(LWP).The test results showed that Cond and Tr were the best,followed by Pn,and Ci fluctuated greatly.Therefore,it was not recommended to use canopy-air temperature difference to predict Ci.The osmotic regulator chlorophyll,malondialdehyde,soluble sugar and proline all performed best with 525mm irrigation quota.The canopy-air temperature difference can better reflect the changes of various osmoregulatory substances,and the optimal fitting results are malondialdehyde,chlorophyll,proline and soluble sugar,respectively.(6)The calculated of CWSI model by the theoretical method and the empirical method has a similar change trend,both of which fluctuate between 0 and 1.The optimal quato of irrigation was 525mm.During in jointing stage to grouting empirical method CWSI were 0.25and 0.35,theory method were 0.17 and 0.14,at end of the grain filling stage experience method of grouting CWSI were 0.55 and 0.52,theory method was 0.49 and 0.46,respectively,on Xindong22 and Xindong43 of winter wheat under drip irrigation in northern.The empirical method is more sensitive to water.Two kinds of CWSI model with soil water potential,leaf water potential and stomatal conductance were significantly negative(P<0.05),and malondialdehyde was significantly positive correlation(P<0.05).(7)The highest yield and better grain quality could be obtained under 525mm~600mm irrigation.The SWP in 20-60cm soil directly below the corresponding drip irrigation belt was maintained at-20KPa~-24KPa at the jointing period,and from heading to the end of grain filling period should be maintained at-32KPa~-60KPa.At the jointing period should be maintained at-23KPa~-25KPa and from heading to the end of grain filling period should be maintained at-48KPa~-82KPa at the distance of 15cm from the drip irrigation belt.Xindong22 and Xindong43 obtained the maximum yields of 12150.6Kg/hm~2 and12111.9Kg/hm~2 respectively when the CWSI was 0.37 and 0.41. |
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