Effects Of Seasonal Freezing And Thawing On Soil Mechanical Stability Aggregates And Organic Phosphorus In Apple-pear Orchard

Seasonal freezing and thawing alternation is a common natural factor that affects the physicochemical properties of soil.Furthermore,the effect of freezing and thawing alternation on soil aggregates is the most direct and effective.Due to the particularity of the climatic and geographical location of Yanbian and the uniqueness of pear varieties,the apple-pear orchard soil undergoes repeated freezing and thawing,making the process of distribution,mineralization and transformation of soil mechanical stability aggregates and organic phosphorus different from those of orchard ecosystems in other regions.The changes of phosphorus content in the soil aggregates of apple orchards before and after seasonal freezing and thawing were determined using the modified Bowman-Cole method.It provides theoretical support for the improvement of apple-pear orchard soil and the apple-pear yield and quality.The results showed:1.Under the condition of seasonal freezing and thawing,the indexes of percent mechanical stability aggregate size,mean weight diameter(MWD),geometric mean diameter(GMD),and fractal dimension D of soil agglomerate in apple or-chard were in the 0-20 cm soil layer.There are freeze-thaw cycles on 20-40 cm and 40-60 cm soil layers.The effect promoted the stability of agglomerates,but with the increase of soil depth,the amplitude of each agglomeration index gradually decreased,and most indicators on 40-60 cm soil layer had no significant difference before and after freeze-thaw.2.Except for the 0-20 cm soil layer,the percentage content of agglomerates in each soil layer showed large aggregates and small aggregates transformed to medium-sized aggregates after freezing and thawing.3.Seasonal freezing and thawing increased the soil activity and high stability of orchard in the 11th,25th and 40th years;a reduction in the percentage of stable organophosphorus was observed.There was no significant change in the percentage of organophosphates in the total organic phosphorus extracted from orchards and wasteland samples in 50th years and 60th years.4.Soil samples from 11,25,and 40-year-old apple-pear orchards showed an increase in the amount of active organic phosphorus after freezing and thawing.While the other forms of organic phosphorus mainly increased,the organic phosphorus reserves in various forms of soil samples in 50 years and 60 year apple-pear orchards and in the wasteland were not significantly changed after seasonal freezing and thawing,and were mainly dominated by the decrease in the amount of organic matter.It can be seen that seasonal freezing and thawing is beneficial to the occurrence of active organic phosphorus to a certain extent,but it has an inhibitory effect on the occurrence of other forms of organic phosphorus.