Study On The Dynamic Evolution Of Orchard Ecosystem On The Weibei Dryland

With the rapid development of apple orchard area, aiming at the problems that how the evolution of the orchard ecosystem is and whether the orchard can be lasting development, choosing the orchards with different planting year in Changwu experimental demonstration area in Shaanxi, the evolution laws of mineral N of soil and changes of soil water content were studied in different planting year. And the regulation approach of orchard ecosystem was exploring preliminarily to provide theoretical basis for promoting the healthy development and benign cycle of orchard ecosystem. The main results are as follows:The mineral N accumulation and distribution of apple orchard soil in different planting year was studied, and the results showed that: 1) the content and distribution of NH₄⁺-N maintain relatively stable in the depths of 0⁴00cm soil profile with different planting years. 2) The content and distribution of nitrate nitrogen varied significantly in the depths of 0⁴00cm soil profile with different planting years., and the content of nitrate nitrogen were 0.31～195.32 mg·kg^-1. The accumulation of nitrate nitrogen increased significantly, which located above 3m. At present the nitrate nitrogen was not leaching to the soil profile that more deep than 3m yet. Generally, the location of accumulation was in 40～260cm depths, and the maximum nitrate N content was 195.32mg·kg-1 in 100～120cm depths of 15 age orchard. With the increase of the planting year, the depth that the accumulation peak appearing was downward shift and the rate of downward shift decreased. The most fast shifting down rate was in 6～10 planting year (5cm/y), and the most slow shifting down rate was in26～37 planting year (0.18cm/y) which was 1/28 of 6～10 planting year. Currently, the most deep soil profile that the accumulation peak appearing was 180cm.The study on the soil water content of apple orchard ecosystem in different planting year showed that: 1) affected by precipitation, the soil moisture had great change in 0²m soil layer, and there was a significant difference among 0⁴0cm, 40⁸0cm and 80²00cm. In the growing season of the apple tree, the leaching depth was less than 2m in normal precipitation, and the changing range of soil moisture was small and tended to be stable under 2m soil layer. 2) The water content of each soil profile was far lower than the field moisture capacity (24%) in the orchard with different planting year. With the increase of the planting year, the soil water content decreased rapidly, and desiccation of deep soil layer appeared. The soil water content of 200cm～300cm soil layer was approach to wilting moisture 9% so the soil water basically had no effects on the apple trees.The study on the effects of different surface mulch on the soil water and the soil temperature showed that with different types of surface mulch, the evaporation of soil water of orchard decreased, and the capacity of soil water conservation improved and the surface mulch had certain regulation function on the soil temperature. 1) Effects on soil water. The water holding effects of plastic film and mixed sand and stone was the best, that of straw tool the second place and that of growing grass was the last. The concrete manifestation was that, in the upper soil layer of the main water absorption of the apple tree root system, compared to the control, the average water content of soil that covered by plastic film and mixed sand and stone increased 1.1%, 0.9% respectively during July to December; and that of soil covered by straws increased 0.7%; while that of growing grass decreased 0.5%, but it changed range was slight in the whole soil profile and the deep soil water content was higher. 2) Effects on soil temperature. The mixed sand and stone had a certain thermo-keeping effect on orchard soil in winter and had some regulation function in summer; the plastic film showed better thermo-keeping effects in the whole year; covering with straws, the soil temperature was higher in autumn, and its rally rate was slow in spring, and soil temperature was lower in hot summer; covering with the growing grass played a role in balancing the soil temperature that the soil temperature increased in winter and decreased in summer.