Simulation Of Water Productivity Of Rainfed Apple Orchard On Semi-Humid Areas Of The Loess Plateau

The planting area and yield of apple occupied the national first place on semi-humid areas of the Loess Plateau, which was the new apple production base. Apple tree is a perennial, deep roots and high water consumption plant, and due to its strong consumption of soil water, soil desiccation happened quite frequently at this zone, which threatened seriously to apple yields and quality improvement. In order to overcome and slow down the effects of high-intensity water consumption, then promote deep soil moisture to improve gradually, we found that these kinds of apple orchards should be treated through establishing adapted water management system with local precipitation conditions, and finding out the variation of apple productivity and soil moisture in apple orchards under different management modes, and selecting the reasonable growth and utilization years of apple orchard which adapt to the local rainfall resource. All of these answered many scientific and technical problems, which helped to update and efficiently reuse the dried apple orchards.We used the field soil water observation combined with EPIC model simulation to study soil desiccation characters of apple orchard on the semi-humid areas of the Loess Plateau. Firstly, we investigated soil moisture on different growth age apple orchards and analysed soil desiccation characters at Baoji and Luochuan, two typical areas on semi-humid areas of the Loess Plateau. Secondly, we used EPIC3060 model developed by USA to simulate the changes of yield and deep soil desiccation of 1～40-year-old apple orchard at Baoji and Luochuan station, on the basis of creating different kinds of databases, such as the daily weather elements series, the typical profile of physicochemical properties of soil, the crop growth parameters, the field tillage measures, the fertilizer characteristic parameter and cropping system database, which could help quantitatively analysis the dynamic change of annual yield and the soil moisture in deep soil layer. According to the quantitative simulation of long period results, we could select the reasonable growth and utilization years of apple orchard that adapted to Baoji and Luochuan station. The main progresses were as follows:1. Field experimental results in Baoji and Luochuan showed as following:(1)The soil moisture in the 0～1000 cm soil layers of apple orchards 10～27 years old at Baoji station was in good condition, and it did not happen soil desiccation. However, the soil moisture decreased in 0～10 m soil layers with the growth years of apple trees, and was a bit poor compared to winter wheat field.(2)11～43 year-old apple orchards occurred with varying degrees of soil desiccation in 0～1500 cm soil layers at Luochuan station. As the soil moisture decreased, the thickness of drying layers increased and became deeper gradually with the growth years of apple trees, and the maximum distribution depth of desiccated soil layer over 1500 cm, but the desiccation rate slowed down from 52 mm per year in 15 year-old apple orchard to 6.8 mm per year in 43 year-old apple orchard.2. EPIC model simulation results showed as following:(1)During the simulation period, the annual rainfall and mean annual consumption of soil water showed a decline tendency with fluctuation as a whole at Baoji and Luochuan stations, and mean annual consumption of soil water was higher than mean annual rainfall in the beginning 20 years, but the trends were consistent or anastomotic between annual rainfall and annual consumption of soil water in the later 20 years.(2)During the simulation period, fruit yield showed a decline tendency with fluctuation as a whole from 4 year-old orchard to 40 year-old orchard during the simulation period. The fruit yield increased gradually in early fruit phase, and reached the highest value during the full phase, then decreased obviously with the fluctuation of annual rainfall. The fruit yield value was higher in Baoji station than that in Luochuan station in every period, and the full phase could keep on to 23 year-old apple orchard in Luochuan station, however, it could keep on to 30 year-old apple orchard in Baoji station. Water stress days of 1～40 year-old apple orchards showed an upward trend which was opposed to the change trend of annual rainfall, and water stress days in Luochuan were more than that in Baoji. 12 year-old apple orchard began to appear water stess days in Baoji, and 10 year-old apple orchard in Luochuan.(3)During the simulation period, the monthly available soil water contents in 0～1000 cm soil layers declined obviously. However, the fluctuation range was higher in the beginning period than in the later period.(4)In semi-arid regions, as the soil moisture decreased in 0～1000 cm soil layers, the thickness of drying layers increased and became deeper gradually with the growth years of apple trees and the deeper of apple roots distribution, and the depth of drying layers distribution was more than 1000 cm in 20 year-old apple orchard. However, rainfall infiltrated no more than 200 cm and there was no water supply below 200 cm soil layers, so soil water content in 200～1000 cm soil layers was stable relatively after 20 year-old apple orchards, and it kept to 30 year-old apple orchard in area which had a better precipitation conditions. When apple trees grew to 23 years, soil water in 200～1000 cm soil layers almost could not be used by apple trees, and soil water in 0～200 cm soil became the main water resources for the growth of apple trees. Therefore, soil water content varied sharply with the variation of annual rainfalls in 0～200 cm soil layers, and soil water content in 200～1000 cm soil layers was close to the local soil wilting poin.(5)In sum, the degrees of soil desiccation of apple orchard were in light desiccated and middle desiccated levels on semi-humid region, and apple tree grew in a relatively good soil moisture environment, so the reasonable growth and utilization years of apple orchard is from 20 years to 30 years.