Effects Of Freeze-thaw Conditions On Nitrogen And Phosphorus Nutrient Migration Characteristics In Sandy Soil

Phosphorus nutrients in sandy soil,indoor simulated freezing-thaw tests were carried out.We controlled the freezing and thaw cycles and freezing and thaw temperature of different depths of sand soil,and analyzed the migration and transformation of nitrogen and phosphorus nutrients.The main research achievements of the paper are as follows:(1)Freeze-thaw cycle times has no significant effect on soil total nitrogen content,from not freeze to thaw cycle after 7 times,the depth of the total nitrogen content change not more than 0.1g/kg,thaw microbial activity in the soil death at low temperature,the melting temperature inactivated microorganisms will release its organic compounds in the body,increase the activity of microorganisms,total nitrogen content in the soil will be stable.Freeze-thaw cycle under the number of soil phosphorus content reduction,test soil perennial by the freeze-thaw cycle,soil microorganisms gradually adapt to the low temperature environment,use from plant rot roots,retained microorganisms released organic material,get the activity quickly recover,after the initial effective phosphorus content increase,after the freeze-thaw cycle,the physical structure of the soil changes,aggregate stability decline,aggregate content reduction,effective phosphorus content reduction.(2)Soil total nitrogen content gradually decreased with increasing soil depth.No freeze-thaw conditions from 0-20 cm with 10% to 40-60 cm and decreased by 26.35% and 23.3%,respectively.The reduction of 15% moisture content from 0-20 cm to 40-10-60 cm by 37.8% and 28.6%,respectively.Surface soil due to plant roots of organic matter content and animal and plant body decomposition makes the fertile soil,organic matter content will increase,the surface soil total nitrogen content is high,deep soil long lack of material exchange with the outside world,the microbial decomposition in soil,nitrification reaction,will consume a lot of nitrogen,nutrient is not easy to be retained,the deep total nitrogen content is low.As the depth of soil increases,the soil will decrease.With the increase of the depth of soil layer,the physical structure of soil has obvious stratification phenomenon.The particle structure of surface soil is loose,which can effectively adsorb hydrogen phosphate and phosphate ions.The structure of deep soil particles is dense and not easy to adsorb,so the effective phosphorus content is low.(3)Soil moisture content did not have a significant influence on soil total nitrogen content under freezing-thawing conditions.After seven freeze-thaw cycles of 0-20 cm,20-40 cm and 40-60 cm,the total nitrogen content of 10% and15% was 0.05g/kg,0.11g/kg and 0.01g/kg,respectively.With the increase of freezing and thawing times,the residual microorganisms in the soil adapt to the freezing and thawing conditions,the soil aggregate structure becomes stable,and the change of soil moisture content on the soil aggregate becomes smaller,so the soil moisture content has less and less influence on the soil total nitrogen content under the action of freezing and thawing.The effective phosphorus content in the soil is unstable at both low and high water content.With the increase of freezing and thawing times,the expansion of ice crystals occupies the soil pores,the transfer space of water to the surface soil becomes smaller,the distance becomes longer,the aggregate is crushed by a large number of ice crystals,the stability of the agglomerates decreases,the aggregate content is unstable,and the change of effective phosphorus content is unstable.(4)Under the change of soil freezing temperature,there was no significant effect of soil total nitrogen content,and the change of soil total nitrogen content was around 0.1g/kg.During high freezing,the mineralization of organic nitrogen is divided into inorganic nitrogen.The organic nitrogen content is reduced,and the mass conservation is formed,and the soil total nitrogen content will remain unchanged.In the soil with high moisture content,the total nitrogen content decreases due to the influence of freezing temperature.The soil with the higher the moisture content breaks down seriously in the process of freezing and thawing,and a large amount of inorganic nitrogen is released,resulting in less total nitrogen content.Freeze-thaw temperature significant influence on effective phosphorus content,freeze-thaw temperature will change the soil temperature change rate,the greater the freeze-thaw temperature difference,the soil volume expansion changes obviously,there will be soil cracks,soil of the compaction will reduce,the microbial activity will be temporarily affected,soil organic matter mineralization and decomposition process block,effective phosphorus content will decline.