Study On The Effects Of Irrigation Lower Limit On Orchard Soil Moisture And Physiology Of Young Apple Trees Under Drip Irrigation

Shanxi Province, as one of the main apple production areas of China,the current situation of its tight water resources supply and extensive irrigation mode affect fruit production and income increasing of peasantry.At present, drip irrigation has been widely used in the field of economic crops because of its characteristics such as water saving, increasing production and so on,but it seldom used in fruit trees.The effect of drip irrigation lower limit on orchard soil moisture and physiology of five year old JINFU No.1 apple trees on dwarf rootstock were studied in this paper,ground irrigation was taken for comparison.Finally, the volumetric soil moisture rate prediction model was established to be applied to the field irrigation.The following conclusions are drawn in the paper:(1)Research of the effect of different irrigation limits on the soil moisture in the orchard indicated that:①Under drip irrigation,the different vertical depth of volumetric soil moisture rate changes dramatically in the shallow and middle layer, deep layer tends to be stable, the different radial distance volumetric soilmoisture rate changes dramatically near the drip irrigation pipe,and changes moderately in the distance.The higher the lower limit of irrigation during the experiment, the higher volumetric soil moisture rate is.②The dynamic rules of vertical and radial volumetric soil moisture rate under drip irrigation and ground irrigation were generally similar.Just in some determination of position,there were slight differences under two irrigation methods.③According to the soil moisture can be roughly divided into 5 period from May to October: Slow soil moisture consumption period(May),Accelerated soil moisture consumption period(June), rapid soil moisture consumption period(July to August),Stable soil moisture period(September to October). so it should be appropriately increased the irrigation times from June to August to ensure the moisture content in the soil,reduced the irrigation times in May, September and October in order to achieve the purpose of saving water.(2)Research of the effect of different irrigation lower limit on physiology of young apple trees indicated that:①Under drip irrigation,the changes of physiological indexes of different irrigation lower limits are different,the monthly average photosynthetic rate,transpiration rate and stomatal conductance were showed as a single peak shape,the monthly average water use efficiency was showed as a “U” shape, while the monthly average early morning leaf water potential was showed as a inverted "N" shape.The higher irrigation lower limit is, the higher the monthly average photosynthetic rate, monthly average transpiration rate, monthly average stomatal conductance and monthly averageearly morning leaf water potential were, while lower the monthly average water use efficiency was.②The changes of physiological indexes under drip irrigation and ground irrigation were generally similar.Just in some period,there were slight differences under two irrigation methods.③The analysis of the main components of various physiological indexes of young apple trees under drip irrigation indicated that the suitable irrigation lower limit reference value for young apple tree was 60% of field water holding capacity.(3)Research of the prediction model of volumetric soil water rate of orchard under drip irrigation indicated that:The multiple linear regression model of volumetric soil water rate is:321????0470041069404035 X.X.X..Y,Y is the current volumetric soil moisture rate,X1 is the former volumetric soil moisture rate,X2 is the amount of irrigation,X3 is the amount of precipitation.The structure of BP neural network model of volumetric soil moisture rate was 6-11-1,the input variable were the factors that influence volumetric soil moisture rate, and the output variable was the current volumetric soil moisture rate.It was proved that the two volumetric soil moisture rate prediction models were all feasible,the difference was existed only in the prediction accuracy.In the practical application, different prediction models were used to obtain the current volumetric soil moisture rate according to their own situation.It is determined whether the current volumetric soil moisture rate has reached the irrigation lower limit.If it has not reached the lower limit of irrigation,irrigation was not needed.Conversely,irrigation was needed.