Soil Water Dynamics And Evapotranspiration Of Hilly Apple Orchard In The Loess Plateau

In order to alleviate soil drought and develop cultivation techniques for apple orchards in loess hilly area of northern Shaanxi Province.We need to analysis dynamic characteristics of soil moisture content and the demand and consumption regular patterns of apple orchards.In this study,a Red Fuji apple orchard in Mizhi Mountain in northern Shaanxi was used as the research object.A comprehensive soil moisture monitoring method was used in combination with FDR,neutron moisture meter and oven-drying to determine the general characteristics of soil moisture in the loess hilly apple orchard.Based on the observation of the evapotranspiration process,the soil water dynamics,canopy interception characteristics,trunk flow and its meteorological factors,we can provide guidance for the efficient utilization of limited rainfall and improve fruit production and fruit quality,so that the mountain apple industry can achieve ecological and economic sustained and healthy development.The main conclusions are as follows:The soil drought in the mountainous area of northern Shaanxi was serious,and the degree of soil drought in spring was highly dependent on soil water storage in the last winter.The water content in the depth of 20,40 and 60 cm soil layer was characterized by seasonal variation similar to that of rainfall.Soil moisture in the 0~60 cm soil layer(root-zone layer)varied with rainfall and had seasonal variation characteristics,but lagged behind that of rainfall.The effect of rainfall on the variation of soil moisture weakened with increasing soil depth.Soil moisture in soil layer below 200 cm was relatively stable,but soil desiccation occurred in 6-year-old apple orchard in the hilly region.There was an obvious low humidity layer in the 90~300 cm soil,where volumetric soil water content was less than 12% for the whole year.Soil moisture at different sites increased with sampling distance from apple tree and along the rows it was significantly higher than that at equivalent distance along the plant(P < 0.05).Using ground cover measures can effectively reduce the evaporation of soil moisture and enhance the ability of water storage which would increase the soil water content of orchard and alleviate the contradiction between water supply and demand of growing season fruit trees.Compared with CK(no mulching or irrigation),dry-farming measures such as the straw mulching,ridge film mulching and furrow rainwater harvesting and organic fertilizer mulching lead to the soil water content in the 0 ~ 60 cm soil layer was 14.7% ~ 16.9%,21.2% ~ 22.5% and 17.9% ~ 20.9% higher than that of the control.And in the 60 ~ 200 cm soil layer,straw mulching,ridge mulching and furrow irrigation and organic fertilizer cover make the soil water content growth to 8.9% ~ 9.3%,13.6% ~ 15.4% and 10.3% ~ 12.3%,respectively.To a certain extent,these dry-farming measures were recommended for dealing with the issue of soil water supply and demand,especially during plant growing season.Among the measures,ridge film mulching and furrow rainwater harvesting had the highest degree of preservation of soil moisture.Thus ridge film mulching and furrow rainwater harvesting was recommended as the most effective agricultural measure in preserving soil moisture in rainfed apple orchards in Loess Hilly Areas of northern Shaanxi Province.The canopy has an important effect on the redistribution process of the orchard.In the process of rain redistribution,the maximum rainfall was observed,the canopy interception was the second,and the stem flow was the smallest,accounting for 72.1%,24.4% and 3.5% of the total precipitation respectively.With the increase of rainfall level,the rainfall intensity,transmittance,canopy interception and trunk stem flow were increased,but the canopy interception rate decreased.In the same rainfall stage,the different growing period of apples had a significant effect on the variations of redistribution of rainfall.The rate of penetrating rain decreased first and then increased while the canopy interception increased first and then decreased with time.During the whole growing season,there was a negative correlation between the rate of light transmission and canopy rejection.Changes in transpiration rate can be expressed by changes in apple tree sap flow rate.The flow rate in the sunny day was a single peak curve,in night it was kept at a level of 0,reaching a peak at 10: 00-14: 00.In rainy days the flow rate curve show obvious diurnal variation characteristics,but its daily variation is irregular,for the lower level of the multi-peak curve,the peak time is uncertain.Solar radiation,temperature,wind speed,relative humidity and soil water content are important factors which have influence on the flow rate of fruit trees.During the growth period,the flow rate of apple trees was positively correlated with solar radiation,temperature,wind speed and soil water content,and negatively correlated with relative humidity.During the growth period,the evapotranspiration was the first to increase and then decrease.And the contribution amount for evapotranspiration was the canopy interception < the fruit transpiration < the soil evaporation.The soil evaporation and fruit transpiration were in the growth period were both increase first and then reduce.The crop coefficients at the different developmental stages of the experimental orchard of germination,flowering period were 0.26,shoot growth and young fruit development period were 0.35 and fruit enlargement period was 0.47.Orchard water revenue and expenditure imbalance,atmospheric rainfall cannot meet the water demand of orchards.