Simulation Of Water Productivity And Soil Desiccation Of Dryland Apple Orchard On Semi-humid And Prone Drought Areas Of The Loess Plateau

The semi-humid and prone drought areas located in the central Loess Plateau became the new apple production base which was rapidly expanding. The low precipitation and the strong water consumption of the apple growth lead to the phenomenon of soil desiccation appeared and stronged gradually that seriously threatened the sustainable development in apple production. In this study, the deep soil moisture of the apple orchards which plant different years were measured, compared and analyzed the deep soil desiccation characteristics of dry and irrigateed apple orchards and compared the dry and irrigateed apple orchards with wheat stubble in soil desiccation intensity to investigate occurrence rule of soil desiccation under the different land use and the different management at Xifeng and Yanan in semi-humid and prone drought area of Loess Plateau. In virtue of EPIC3060 model developed by the United States has set up a series of databases of Xifeng and Yanan in semi- humid and prone drought area of Loess Plateau such as the daily weather elements database, the typical profile of physical and chemical properties of soil database, the crop growth parameters database, the field plowing database, the fertilizer and planting system parameters database. The WinEPIC model simulated the dynamic changes of water productivity and soil desiccation effects of dryland apple orchards at Xifeng and Yanan during 1960~1999 , revealed the occurrence rule of decicated soil layer and effects of soil desiccation on apple productivity, determined the reasonable utilization period adapted to the different ares to provide the scientific basis for sustainable use of soil water and healthy development of apple production base in apple orchards of Loess Plateau. The main study results are as follows:1. Field results in Xifeng showed that:(1) The soil decication intensity of apple orchard was stronger than the stubble wheat. The soil water amount of wheat stubble in 0~1300 cm soil profile was 2065 mm which was higher than the average(2014 mm) of 12 year-old ,18 year-old and 26 year-old apple orchards. Wheat stubble that the soil water consumption was 119 mm which was less than the average(249 mm)of 12 year-old, 18 year-old and 26 year-old. The depth of desiccated soil layers of wheat stubble reached 440 cm was shallower than the average(880 mm)of 12 year-old, 18 year-old and 26 year-old apple orchard. (2) The soil moisture of 26 year-old irrigation orchard was 11.7% which was higher than the apple orchard of 18 year-old and the depth of desiccated soil layers of 26 year-old irrigation orchard reached 1040 cm was shallower than 18 year-old apple orchard and soil desiccation intensity(slight desiccation ) of 26 year-old irrigation orchard was lighter than 18 year-old.2. Field results in Yanan showed that:(1) Dryland orchard under the same planting density that the soil water moisture in 0~1000 cm soil profile decreased annually and the desiccated soil layers became thicker and deeper with planting ages. The depth of desiccated soil layers of 12 year-old and 20 year-old had reached 800 cm and 1000 cm respectively. Soil desiccation intensity from slight desiccation (12 years) to moderate desiccation (18 years).(2) The soil desiccation intensity of 16 year-old apple orchard that the spacing is 3 m×4 m was stronger than the 12 year-old and 20 year-old apple orchard that the spacing is 4 m×5 m. The soil water amount of 16 year-old in 0~840 cm was 1290 mm which was less than the average(1389 mm) of 12 year-old and 20 year-old apple orchards and the soil water consumption was 400 mm which was more than the average(237mm)of 12 year-old and 20 year-old apple orchards.3. Simulation results showed that:(1) Apple yields all decreased obviously with fluctuation after 10 years'yield reached the highest yield The yield of more than 70% apple orchards had reached the low-yielding orchards (18 t/hm2) and fluctuated unsteadily with precipitation changes after 22 year-old and 23 year-old which average yield were 16.53 and 16.31 t/hm2 respectively at Xifeng and Yanan during the simulation of 1960~1999.(2) The average annual water consumption were higher than annual precipitation from 1 to 23 years, the soil desiccation rates of 1~10 year-old and 11~ 23 year-old orchards were 94 mm/a and 22.6 mm/a, 114 mm/a and 23.9 mm/a respectively at Xifeng and Yanan, which made the monthly available soil water amounts decreased rapidly in 0~10 m soil profile of 1~ 23 year-old orchards. The average annual water consumption were equal with annual precipitation from 24 to 40 years,the monthly available soil water amounts of 24~ 40 year-old orchards at Xifeng and Yanan were 70~240 mm and 281.7~319.2 mm respectively which fluctuated steadily with growth seasons and precipitation changes.(3) Soil moisture fluctuated obviously with precipitation changes in 0~2 m soil profile while it decreased annually in 2~10 m soil profile , therefore, the desiccated soil layers became thicker and deeper at Xifeng and Yanan. The depth of desiccated soil layers of 12 year-old orchard had reached 10 m and soil moisture in these two areas gradually closed to the local soil wilting moisture and then kept steady until 24 years and 21years. Soil desiccation at Xifeng intensified gradually until 24 years when it kept steady and was in strong desiccation state from no desiccation (1 to 6 years) to slight desiccation (7 years) to moderate desiccation (8 to 9 years) to serious desiccation (10 to 11 years) to strong desiccation (after 12 years). Soil desiccation at Yanan intensified gradually until 21 years when it kept steady and was in strong desiccation state from no desiccation (1 to 6 years) to slight desiccation (7~9 years) to moderate desiccation (10 to 11 years) to serious desiccation (after 12 years).In view of analysis of the yield stability and soil desiccation intensity, the reasonable utilization period of dryland apple orchard at Xifeng an Yanan are 22~24 years and 21~23 years respectively.