Effect Of Biochar On Mineral Nitrogen Release In Freezing And Thawing Soil

In the northeastern part of China,frozen soil and snow gradually melt after the temperature rises in spring,and the soil moisture content increases,causing some nutrients in the soil to migrate down with the snow melt water and leaching.Biochar made from straw has good porous structure and physical and chemical properties,and plays an important role in improving soil structure,improving microbial living environment and improving crop yield and quality.Mineral nitrogen is an essential nutrient for crop growth,and it is also prone to loss while being absorbed and utilized by crops.At present,most studies on the effects of biochar on soil nutrient availability focus on the crop growth period,and there are few reports on the effects of biochar application on soil mineral nitrogen under freezing and thawing.Therefore,this study takes two typical soil brown soils and black soils in Northeast China as research objects.Field in situ observation experiments and indoor simulated freeze-thaw tests are conducted in the field to analyze the soil mineral nitrogen content after biochar application under freezing and thawing conditions.And the changes of the occurrence patterns,explore the mechanism of bio-carbon input to soil mineral nitrogen during freeze-thaw period,and further analyze the effect of biochar on soil nutrient availability.The main conclusions are as follows:（1）Field trials in the field showed that the amount of biochar applied had a significant effect on the NH₄⁺-N and NO₃^--N content during the whole snowmelt period.The content of NO₃^--N in different treatments was almost the same as that of NH₄⁺-N during the whole process of snowmelt.The concentration of NO₃^--N in all treatments decreased rapidly on the 4th day before snowmelt,and the order of contents was 6%>4%>2%>CK.（2）The indoor simulated freeze-thaw test showed that the content of NH₄⁺-N in brown soil increased with the increase of biochar application in the four treatments,and the overall performance of NO₃^--N in the 0-20 freeze-thaw cycles increased first.After the reduction.The change rule of mineral nitrogen in black soil is basically consistent with brown soil.（3）Under the same freezing and thawing frequency,the adsorption of NH4+-N by black soil after applying biochar was 8%>6%>4%>2%>CK,and the adsorption of NH₄⁺-N by brown soil was 6%>4%>2%>CK.The number of freeze-thaw cycles has a great influence on the adsorption amount of NH₄⁺-N.The adsorption amount of NO₃^--N in brown soil increased with the increase of NO₃^--N equilibrium concentration under the same freeze-thaw frequency.The adsorption amount of black soil is increased with the increase of the proportion of addition,and it increases after increasing to a certain amount.The amount of NO₃^--N adsorbed by the 8%biochar applied to black soil was less than 4%and 6%.（4）Under the same freezing and thawing frequency,the desorption effect of biochar application on NH₄⁺-N is CK>2%>4%>6%.Under the application of biochar,the desorption effect of NH₄⁺-N in each freeze-thaw frequency is As the frequency of freezing and thawing increases,the soil desorption rate will increase.When the biochar addition ratio is 6%,the adsorption amount of NO₃^--N is the highest and the desorption rate is the lowest.（5）The effects of freezing and thawing and biochar application have certain effects on soil related indicators.The effect of applying biochar on soil conductivity,organic matter and urease activity under freezing and thawing has reached a significant level.From the whole process of freeze-thaw cycle,the correlation between NO₃^--N content and conductivity,organic matter and urease activity were0.796,0.724 and 0.698,respectively.It can be seen that the correlation between NO₃^--N content and conductivity is higher than that.Organic matter content and urease activity.The effect of freezing and thawing and biochar application on the p H of the soil did not reach a significant level.