Investigation On The Surface And Pit Wall Evaporation Of Orchard Under Water Storage Pit Irrigation

With the social development and adjustment of agricultural planting structure in China, the planting area of fruit trees, especially for apple trees, has increased year by year. Shanxi Province as one of the most favorable areas for apple, regional fruit production has become the driving force of the increase in agricultural income. However, water shortages and soil erosion are very serious in Shanxi located in the northwest of the Loess Plateau, which significantly affected the yield and quality of apples and restricted the local economic development and improvement of living standards. Water storage pit irrigation is a new method suitable for orchard irrigation in gully area in the North China, which has many advantages, such as water-saving, water retention and drought-resisting etc.. There has been many researches on water and nutrients transport of orchard under water storage pit irrigation, however, the study on the soil evaporation of orchard under water storage pit irrigation is uncommon. Therefore, in order to understand the water-saving and drought-resisting mechanism of water storage pit irrigation completely, it is important to investigate the soil evaporation of orchard under water storage pit irrigation with both theoretical and field experimental methods.In the present work, the surface and pit wall evaporation of orchard under water storage pit irrigation is theoretically and experimentally investigated on the condition of different pit depths and irrigation amounts. And the following conclusions are obtained:(1) The study of the surface evaporation of orchard under water storage pit irrigation has shown that:Compared with surface irrigation, the surface evaporation intensity of orchard under water storage pit irrigation is small after irrigation, and the difference gradually becomes smaller over time; the variation of soil surface evaporation intensity at different distances from the stem is almost the same, which gradually decreases over time, but the range was small; with the same distances from the stem and pit depth, the variation of surface evaporation is intensity consistent over time, the difference of evaporation intensity is small in the same day; with the different irrigation amounts and the same distances from the stem, soil surface evaporation intensity is consistent over time, the difference of evaporation intensity is small in the same day.(2) With the study of pit wall evaporation of orchard under water storage pit irrigation, it is shown that:①After irrigation the pit wall evaporation intensity increased first and then decreased;②The pit wall evaporation intensity was different at different depths of pit wall, The closer to the pit bottom, the pit wall evaporation intensity was the smaller;③At the same depth of pit wall, the variation of pit wall evaporation intensity ratio is consistent over time, and deep pit (60cm) evaporation intensity ratio was larger than shallow pit (40cm);④with the same pit depth and different irrigation amounts, the variation of pit wall evaporation intensity ratio is consistent over time, the evaporation intensity ratio is almost the same at the10cm,30cm50cm depth below the ground, respectively;⑤compared with surface irrigation, the pit wall evaporation intensity of orchard under water storage pit irrigation is smaller after one week, and the humidity is large, which is main reason for the difference of the pit wall evaporation intensity between surface irrigation and water storage pit irrigation.(3) The study on the influence factors of the evaporation of orchard under water storage pit irrigation has demonstrated that:①for the surface evaporation of orchard under water storage pit irrigation, soil moisture content is the main factor affecting the evaporation intensity, while the impact of weather conditions on the evaporation intensity was not significant, and the surface evaporation of orchard under water storage pit irrigation has a exponential correlation with soil moisture content, the correlation coefficients are0.864,0.708,0.641for at the distances of10cm,30cm,50cm from the stem, respectively.②for the pit wall evaporation of orchard under water storage pit irrigation, relative humidity is the main factor affecting the evaporation intensity, while the impact of soil moisture content and weather conditions on the evaporation intensity was not significant, and the pit wall evaporation of orchard under water storage pit irrigation has a logarithmic correlation with soil moisture content, the correlation coefficients are-0.746,-0.689,-0.748for at10cm,30cm50cm depth below the ground, respectively.(4) Based on the least squares support vector machines(LS-SVM), the models for calculating the surface and pit wall evaporation of orchard under water storage pit irrigation are developed, respectively. The results calculated by the two models agree well with the values measured in the field tests, which demonstrates the two models established in the present work have high prediction accuracy. It is shown that the model with five input factors i.e. soil moisture, temperature, humidity, wind speed and radiation is of higher precision than that with three input factors i.e. soil moisture, temperature, humidity.