Measurements And Modeling Of Canopy Prunings On Water Consumption And Production Of Apple Orchards On The Loess Plateau

Apple production in Loess Plateau about a quarter of the world,apple becomes the crucial local industry to building moderately prosperous society due to the good quality and taste.However,more than 80%of the apple orchards located in rainfed（dryland）areas,the high quality development of apple orchards is influenced by the balance between supply and demand due to excessive water consumption.Pruning is widely used in the production of fruit tree as productivity measures,and also as a important moisture control technology.Unfortunately,it is little known about how canopy pruning might regulate orchard transpiration and soil water depletion.We monitor the sap flow,soil moisture and soil evaporation of four pruning intensities,including Control（no summer pruning）,SP-I（light pruning,remove 10%lateral branch length）,SP-II（moderate pruning,remove 25%lateral branch length）and SP-III（severe pruning,remove 40%lateral branch length）.Combining with model simulations（MAESPA）,the effects of different pruning intensities on apple tree evapotranspiration and profile soil moisture dynamics in the Loess Plateau,fruit tree growth,yield and water use efficiency were analyzing,and aim to provide helpful information for water management and sustainable development of apple orchards.Results show that:（1）Overall,the diurnal sap flow displayed a single peak with weakly fluctuate on sunny days and multiple peak with strongly fluctuate on cloud days.Canopy pruning significantly changed the daily transpiration,and the peak value of severe pruning（SP-III）treatment decreased by about 40%compared with the control.The MAESPA model also captures the transpiration difference between different pruning intensification and get good performance in diurnal and seasonal scale.There was no significant difference between different treatments of soil evaporation（P>0.05）.MAESPA model also showed a good performance of the variations of soil evaporation.（2）The surface soil moisture fluctuated greatly,but there was no significant difference between different treatments,but canopy pruning has significantly changed the subsurface water distribution（P<0.05）.In the range of 20-60 cm,the average soil content of SP-I,SP-II and SP-III increased by 6.7%,14.6%and 23.4%respectively.Within 60-120cm,the average soil content of the three pruning intensities increased by 8.9%,23.1%and 25.6%,respectively,compared with the control.MAESPA model well simulated the change of measured soil moisture,and the new simulation strategy based on HYDRUS model after removing surface runoff further improved the accuracy of soil moisture simulation.By simulating the process of soil water transport with different treatments in different precipitation years,it is found that pruning can alleviate the loss of soil water deficit to a certain extent and supplement soil water in normal years.In dry years,only heavy pruning（SP-II,SP-III）can alleviate soil moisture deficit.（3）Canopy pruning has a great effect on photosynthetic characteristics of apple tree leaves,and pruning promoted photosynthetic rate,stomatal conductance and transpiration rate,but pruning has no significant effect on fluorescence parameters of leaves such as J_maxand V_cmax.MAESPA can roughly reflect the changes in photosynthetic rate,but model underestimated the measured values at noon.Pruning promoted the fruit growth to some extent,but the excessive pruning intensity resulted in the decrease of fruit diameter.Pruning promoted yield and water use efficiency,and the yields of light pruning（SP-I）and moderate pruning（SP-II）increased by 22.1%and 6.4%,respectively,compared with control,while severe pruning（SP-III）was significantly lower than light pruning（P<0.05）.WUE of light and moderate pruning was significantly higher than that of severe pruning and control（P<0.05）,and moderate pruning was 18.7%higher than that of control.In summary,in wet years,we suggest light summer pruning,i.e.removing about 10%of lateral water sprouts,overlapping branches and twigs.In normal precipitation years,moderate pruning,i.e.removing approximately 25%of lateral branches can alleviate water deficit and improve water use efficiency.In severe drought years,heavy pruning,i.e.removing approximately 40%of lateral branches,is strongly recommended to improve water use efficiency and reduce deep water consumption,avoid hydraulic failure,and promote the green and healthy development of orchards.