Effects Of Freeze-thaw On Organic Phosphorus Fractions In Soil Of Apple-pear Orchard In Longjing City

In order to explore the effect of freezing and thawing on soil phosphorus,we need to further understand the organic phosphorus cycle in apple-pear orchard soil and make up for the lack of research on organic phosphorus in northern orchards.We collected soil from the orchards of Longjing City,Yanbian Korean Autonomous Prefecture for 11 years,25 years,40 years,50 years,and 60 years for our experiments.In the fall of the first year and the spring of the second year,we collected soil samples at depths of 0-20 cm,20-40 cm,and 40-60 cm to perform the seasonal freeze-thaw contrast test.We used freeze-thaw cycles,freezing temperatures,and soil-water content as experimental factors,using the "3414" experimental design to perform the freeze-thaw alternate indoor simulation test.The modified Bowman-Cole method was used to determine the contents of different forms of organophosphorus in the soil of spring and autumn of Longjing apple-pear orchard and those treated by freezing and thawing.The organophosphorus compounds in soil were determined by 31P-NMR.The results presented the following:1.Seasonal freezing and thawing has the greatest effect on moderately stable organic phosphorus.As the soil layer deepens,the content of each organic phosphorus component gradually weakens due to seasonal freezing and thawing.Seasonal freezing and thawing mainly tends to affect the conversion between different organophosphorus components in the same soil layer.The different organophosphorus components in different soil layers are affected by seasonal freezing and thawing.2.The effect of seasonal freezing and thawing on phosphorus compounds weakens as the soil depth deepens.Affected by seasonal freezing and thawing,the absolute content of orthophosphates,phosphate monoesters,orthophosphate diester,and pyrophosphates increases to varying degrees.In terms of relative content,the orthophosphate and phosphate monoesters tend to have opposite trends after being affected by seasonal freeze-thaw cycles.3.Except for the 40-60 cm soil layer in the orchard for 50 years,the three freeze-thaw simulation experiments have affected the organic phosphorus content in the soil of five apple-pear orchards in Longjing City.The initial soil moisture content has the greatest effect on organic phosphorus,the soil freeze-thaw cycle is second,and the freezing temperature has the least influence on organic phosphorus.4.There are two trends in the influence of freezing and thawing factors on the organic phosphorus components of soil.The first is that as the code value of freezing and thawing factors increase,the change in trend of the organic phosphorus components presents a downward-looking parabolic shape.That is,as the code value of freeze-thaw factor increases,the content of organic phosphorus components increases first and then decreases.Second,when setting two freeze-thaw factors at a low level(code value 0)or a high level(code value 3),as the code value of the third freeze-thaw factor increases,the content of each organic phosphorus component tends to show the opposite trend.When setting two freeze-thaw factors to a medium level(code value 1 or 2),with the increase in the code value of the third freeze-thaw factor,the content of each organic phosphorus component does not change significantly.5.Soil at depths of 20-40 cm are more affected by freezing and thawing than soil from depths of 0-20 cm and 40-60 cm.6.Orchard soil of 40 years were affected by freeze-thaw significantly more than other orchards.