Effect Of Straw Biochar On The Loss Of Inorganic Nitrogen And Phosphorus In Surface Layer Of Black Soil During Freezing And Thawing Period

Inorganic nitrogen and phosphorus in soil can be directly absorbed and utilized by plant roots,which is the most active factor in soil fertility,one of the main limiting factors affecting plant growth and crop yield.Due to its unique geographical location,the northeast black soil area has special environmental characteristics such as large snowfall in winter,severe snowmelt erosion in spring,and obvious freezing and thawing effects.The melting of snow on the surface during the spring thawing period not only causes serious loss of water and soil resources and inorganic nutrients,but also causes problems such as soil quality degradation and water body eutrophication,and even directly jeopardizes the sustainable use of soil and the healthy development of the ecological environment.In recent years,There are many researches on the prevention and control measures of nutrient loss in the black soil area,but there is still no targeted research on the prevention and treatment of nutrient loss during the freezing and thawing period.Due to its special physical and chemical properties,biochar can reduce soil erosion and retain soil nutrients.Therefore,biochar is widely used as a soil conditioner for water retention and fertilizer conservation.However,under the effect of repeated freezing and thawing in the black soil region of Northeast China,the role of straw biochar in holding nutrients is still unclear.Therefore,it is very important to explore the effect and mechanism of straw biochar input on the soil and soil and inorganic nitrogen and phosphorus nutrient loss driven by freezing and thawing,which provides some theoretical support for soil nutrient loss and non-point source pollution prevention in the black soil region.In this study,the black soil of sloping farmland was taken as the research object.Through the test methods of simulating soil inorganic nitrogen and phosphorus levels?slope surface?and vertical migration,the freeze-thaw and non-freeze-thaw cycles,freeze-thaw cycles and straw biochar application amount were studied and analyzed in detail.Under the three different influencing factors,the characteristics of migration and loss of water,soil and inorganic nutrients in the surface layer of black soil during freezing and thawing period further elaborated the methods to control the loss of water,soil and inorganic nitrogen and phosphorus in the thawing period of the black soil region in Northeast China,and guided and improved the freezing and thawing of the area.The agricultural non-point source pollution caused by the process has very important strategic and scientific significance.The main conclusions are as follows:?1?the effect of straw biochar input on soil and water loss process of black soil slope during freezing and thawing periodThe freezing-thawing cycle in the spring freezing and thawing period accelerates the time of soil erosion.As the number of freezing-thawing cycles increases,the time for soil erosion occurs longer,and the application of biochar also prolongs the occurrence of soil erosion.The amount of runoff water sample loss gradually increased from 8 to 12 min perunit time from the beginning of production.The freezing-thawing cycle aggravated the cumulative loss of runoff water samples,and the application of biochar effectively prevented the loss of runoff water samples.The amount of runoff sediment loss gradually increased from 7 to 11 min from the beginning of the production flow,and stabilized earlier than the runoff loss.With the increase of the number of freezing-thawing cycles,the cumulative sediment yield increased sharply.The addition of biochar had the most significant effect on preventing cumulative sediment yield under the three freezing-thawing cycles.The cumulative sediment yield was only 75 % of the control group.?2?the effects of straw biochar input on the loss of inorganic nitrogen and phosphorus in black soil slope during freezing and thawing periodDuring the spring thawing period,NO₃^--N,NH₄⁺-N and PO₄^3--P were lost with runoff water samples and runoff sediments,and the loss per unit time increased to the stable stage as the scouring continued.NH₄⁺-N and PO₄^3--P gradually became longer after 5 freezing-thawing cycles or 5 days of culture,and NO₃^--N was lagging behind.The freezing and thawing effect increased the cumulative loss of inorganic nitrogen and phosphorus in runoff water samples and runoff sediments,and the cumulative loss increased significantly with the increase of freezing-thawing cycles.Biochar inhibits the loss of inorganic nitrogen and phosphorus,and NH₄⁺-N is the most prominent.The cumulative loss of inorganic nitrogen and phosphorus in runoff sediment is higher than the cumulative loss of inorganic nitrogen and phosphorus in runoff water samples.The sampling points of the soil trough are much higher than the nutrient concentrations in the runoff water samples and sediment.Under the same situation that the distance between the sampling points and the sampling point is generally the same,the deeper the depth of the soil layer,the higher the concentration;In the case of the same depth of the soil layer,the closer the slope is to the bottom,the higher the concentration.?3?the effect of straw biochar on vertical migration of inorganic nitrogen and phosphate in surface layer of black soil during freezing and thawing periodIn order to explore the effect of straw biochar on the vertical migration of inorganic nitrogen and phosphorus in surface layer of black soil during freezing and thawing period.This research adopts the indoor simulation of freezing and thawing cycle experiment,set the freezing-thawing and non-freezing-thawing,freezing-thawing cycles,biochar apply three influence factors,to analyze the vertical migration characteristics of soil surface inorganic nitrogen and phosphorus under freezing and thawing with different straw biochar with different straw biochar apply.Results show black soil surface freezing-thawing and non-freezing-thawing,freezing-thawing cycles and biochar apply have significant effect on NO₃^--N,NH₄⁺-N and PO₄^3--P inorganic nitrogen and phosphorus migration liquid total volume,total concentration and total amounts of migration through freezing-thawing and non-freezing-thawing,freezing-thawing cycles and biochar apply.The leaching time was shortened with the increase of freezing-thawing action and prolonged with the increase of biochar application.All treatments of inorganic nitrogen and phosphorus migration liquid volume show a decrease trend with the increase of biochar input.The total volume of migration liquid in non-freezing-thawing group show a slowly decrease trend as the incubation period increase.The total volume of migration liquid volume in the freezing and thawing group increases sharply in the 5th freezing-thawing cycle test,and then became stable.The effect of biochar on the vertical migration and accumulation of inorganic nitrogen and phosphorus under freezing-thawing action was analyzed.During the same control period,the inhibition of biochar on the vertical migration of inorganic nitrogen and phosphorus in the freezing-thawing group was greater than that in the non-freezing-thawing group.Because of changes in the physical properties of the soil,the accumulated migration of freezing-thawing group NO₃^--N,NH₄⁺-N and PO₄^3--P changed dramatically around the fifth freezing-thawing cycle.To sum up,biochar can effectively retain nutrients during freezing-thawing period,and the research results can provide some theoretical support for the prevention and control of rural surface pollution during thawing period in cold regions.