Research Of Soil Water-stable Aggregate Of Apple-pear Orchard In Yanbian Area

Yanbian area is the eugenic area for apple-pear production.Its unique climate conditions and the characteristics of pear varieties are different from those of orchard ecosystems in other parts of China.The quality of orchard soil in Yanbian area has become the focus of research.In this paper,aiming at apple-pear orchard soil in Yanbian area,the planting years of 11,25 and 2016 were selected in Longjing City,Yanbian Prefecture in autumn of 2015 and spring of 2016.Soil samples from 40 and 63 years representative apple-pear orchards were collected by layers of 0-20 cm,20-40 cm and 40-60 cm.Soil water-stable aggregates were determined by wet sieve method.Combined with soil average weight diameter(MWD),geometric average diameter(GMD),fractal dimension D,structural damage rate and aggregation degree,soil iron oxide and organic were synthesized.The variation trend of quality,pH and clay content was analyzed.The variation rule and evolution trend of water-stable aggregates with planting years,levels and seasons were comprehensively analyzed.The research results will help to make up for the deficiency of water-stable aggregates research in northern orchards,and have certain theoretical and practical significance for guiding the management of northern orchards.The main results are as follows:1.In autumn,the percentage of soil water-stable aggregates changed from small aggregates to large aggregates and medium aggregates with the increase of planting years of fruit trees,especially in 0-20 cm soil layer.2.Compared with orchard soil,the average weight diameter and geometric average diameter of wasteland soil are larger and the fractal dimension is smaller.However,with the increase of orchard planting years and soil depth,the average weight diameter and geometric average diameter of soil water-stable aggregates increase gradually,and the fractal dimension decreases gradually.3.Seasonal freeze-thaw effect had little effect on soil water-stable aggregates in orchards with lower planting years.In orchards with higher planting years of 40 and 63 years,the water-stable aggregates after freeze-thaw showed an increase in average weight diameter,an increase in structural damage rate and a decrease in aggregation degree.4.Free iron oxide,amorphous iron oxide,crystalline iron oxide,pH and clay content in soil are all important factors causing the change of water-stable aggregates.After seasonal freezing and thawing,the change rule of each factor is consistent with the change of water-stable aggregates.In conclusion,it can be concluded that fruit tree planting is conducive to the formation of large aggregates and intermediate aggregates,and the longer planting time,the more water-stable aggregates formed,the more stable soil structure;seasonal freeze-thaw has less impact on orchards with lower planting years,and has obvious destructive effect on orchard soils with higher planting years,and the stability of soil water-stable aggregates becomes worse after freeze-thaw.The erosion resistance is weakened.