Water Use And Evapotranspiration Estimation Of Apple Under Alternate Partial Root-zone Irrigation In Arid Northwest China

Arid northwest China is an important special fruit production base,but water shortage is the most important limiting factor for fruit production in this area.Improving effective water utilization is a necessity for the sustainable development.Alternate partial root-zone irrigation?APRI?is an innovative water-saving technology,which can reduce luxury transpiration and improve water use efficiency.Therefore,conducting researches on water use and evapotranspiration estimation of apple tree under APRI can provide scientific basis for the establishment of irrigation schedule and promote the development of apple tree water-saving and high-yield,which is of great significance to the sustainable development of economy and ecology in arid areas.Accordingly,two factors' field experiments were conducted on apple trees with three irrigation methods,i.e.alternate partial root-zone irrigation with high frequency?PRIH?,alternate partial root-zone irrigation with low frequency?PRIL?and conventional irrigation?CI?,and two irrigation amounts?400 mm and 500 mm?at Shiyanghe Experimental Station of China Agricultural University in 2013 and 2014.The objectives of this study are to investigate the physiological and morphological characteristics,and the variation of evapotranspiration,yield and water use efficiency under APRI,develop the estimation model to calculate evapotranspiration under APRI and propose the better parameter to indicate the water status of apple trees.The main results are outlined as followed:?1?The differences of the physiological and morphological characteristics under APRI were investigated.Compared with CI,APRI significantly decreased leaf stomatal conductance,and stem and leaf water potentials,but had no significant impacts on photosynthetic rate;improved root length density,root diameter,root surface area and root volume significantly,but had no significant effects on root dry weight;enhanced gap fraction and leaf inclination angle,while reduced leaf area index and clumping index.Furthermore,in comparison of PRIL,PRIH reduced photosynthetic rate,stomatal conductance,stem and leaf water potentials,gap fraction and leaf inclination angle,but improved root parameters,leaf area index and clumping index.?2?The impacts of APRI on apple tree evapotranspiration,yield and water use efficiency were analyzed.In comparison of CI,APRI could significantly increase apple yield and reduce tree evapotranspiration,so it enhanced water use efficiency.Compared with PRIL,PRIH could also improve apple tree evapotranspiration,yield and water use efficiency.?3?The estimation model of apple tree evapotranspiration under APRI was proposed,and the accuracy and usability of the above models estimating apple tree evapotranspiration under different irrigation methods in arid areas were evaluated.S-W_PRI is the suitable optimization model for estimating apple tree evapotranspiration in arid areas that it enhanced the accuracy of the evapotranspiration estimation both under APRI and CI.?4?The feasibility of using the signal intensity based on maximum daily stem shrinkage(SI_MDS)to indicate the water status of apple trees under APRI was assessed.Maximum daily stem shrinkage?MDS?was significantly higher under CI at 400 mm than under APRI at 400 mm,while no difference was found at 500 mm.MDS was significantly positively correlated with meteorological factors,while SI_MDS and the signal intensity based on sap flow(SI_SF)were not.In contrast to SI_SF,SI_MDS was significantly correlated with soil water content as well as midday stem and predawn leaf water potentials under APRI.Furthermore,SI_MDS was significantly lower under APRI than that under CI,while no difference was found in SI_SF between the two irrigation methods.