Effects Of Biochar Addition On Nutrient Leaching From Black Soil And Yellow Soi

Soil nutrient is an important index to reflect the quality of cultivated land and the key to improve farmland yield.Soil leaching is a process in which soluble substances in soil migrate downward with water movement.As an important way of soil nutrient loss,nutrient loss also pollutes the water environment and easily causes agricultural non-point source pollution.Biochar is light,loose and porous,and has been widely used as a soil additive in carbon sequestration,soil improvement and other research fields.The application of biochar is bound to affect the leaching process of soil nutrients.However,the effects of biochar on soil nutrient leaching are not the same due to the difference of biochar properties,application amount and application method,and soil properties.Yellow soil and phaeozem are typical zonal soils in China.The decline of soil fertility caused by long-term tillage and excessive fertilization seriously affects the sustainable development of regional agriculture.How to take measures to control soil nutrient loss and improve soil nutrient status is an urgent problem to be solved.In this study,yellow soil and phaeozem were selected as the research objects,and the soil column simulation test was used to study the leaching characteristics of soil nutrients under different biochar addition amounts,and to reveal the differences in nutrient leaching between unfertilized soil and fertilized soil.The results can provide a useful reference for the application of biochar in soil structure improvement and agricultural production.The main conclusions are as follows :(1)Biochar addition could significantly increase the p H and EC of yellow soil and phaeozem,and the increase rate increased with the increase of biochar content.When the biochar content was the same,the soil p H and EC decreased after fertilization compared with the unfertilized soil.(2)Compared with the control,the cumulative leaching loss of nutrients in Phaeozem decreased significantly after adding biochar.When the addition amount was 1.25 %,the cumulative leaching amount of total phosphorus,total potassium and total nitrogen was the smallest,which decreased by 1.04 %,22.1 % and 35 % respectively compared with the control.When the addition amount was 5 %,the cumulative leaching loss of DOC,nitrate nitrogen and ammonia nitrogen was the smallest,which decreased by 38.3 %,58.8 % and 11.6 %,respectively.In yellow soil,when the addition amount was 1.25 %,the cumulative leaching loss of DOC was the lowest,which was 8.3 % lower than that of the control.When the addition amount was 2.5 %,the cumulative leaching loss of each nutrient index in the leaching solution showed different degrees of increase compared with the control.When the addition amount was5 %,the cumulative leaching loss of nitrate nitrogen was the lowest,which was 8 % lower than that of the control.(3)The combined addition of biochar and inorganic fertilizer had different effects on nutrient leaching under different soil types.In Phaeozem,when the amount of biochar added was 1.25 %,the cumulative leaching amount of DOC and total potassium was the smallest,which decreased by 15.3 % and 45.4 % respectively compared with the control.When the amount of biochar added was 5 %,the cumulative leaching amount of total nitrogen,ammonia nitrogen,nitrate nitrogen and total phosphorus was the lowest,which was reduced by 23 %,10 %,4 % and 10 % respectively compared with the control.In yellow soil,when the amount of biochar added was 1.25 %,the cumulative leaching amount of total nitrogen and nitrate nitrogen was the smallest,which was 56.8 % and 6.6 % lower than that of the control.When the amount of biochar added was 5 %,the cumulative leaching amount of total phosphorus was the smallest,which was 12.4 % lower than that of the control.The addition of different contents of biochar promoted the leaching of DOC,ammonia nitrogen and total potassium.(4)The higher the amount of biochar added in the phaeozem,the higher the DOC content in the soil after leaching,indicating that biochar can significantly reduce the leaching loss of DOC in the phaeozem,while the yellow soil is opposite,showing that the soil DOC content decreases with the increase of biochar addition.Compared with the control,the DOC content increased by 36.9 %,12.6 % and 23.1 % when the addition amount was 1.25 %,2.5 % and 5 %,respectively.The total potassium content of phaeozem after leaching was the highest when the biochar addition amount was 1.25 %,the total phosphorus and total nitrogen content in the soil was the highest when the addition amount was 2.5 %,and the nitrate nitrogen and ammonia nitrogen content in the soil was the highest when the addition amount was 5 %.In yellow soil,the content of nitrate nitrogen was the highest when the addition amount was 2.5 %.The contents of total nitrogen,ammonia nitrogen,total phosphorus and total potassium were the highest when the addition amount was 5 %,which increased by 74.9 %,46.2 %,33.5 % and18.2 % respectively compared with the control.Under the condition of mixed application of biochar and inorganic fertilizer,the higher the amount of biochar added in phaeozem,the higher the content of total nitrogen,nitrate nitrogen,ammonia nitrogen,total phosphorus and total potassium in phaeozem after leaching treatment.In yellow soil,when the amount of biochar added was 1.25 %,the DOC content in the soil was the highest after leaching treatment,which increased by 76 % compared with the control.When the addition amount was 2.5 %,the nitrate nitrogen content in the soil was the highest after leaching treatment,which increased by 23.3 %compared with the control.When the addition amount was 5 %,the contents of total nitrogen,ammonia nitrogen,total phosphorus and total potassium in the soil were the highest,which increased by 61.3 %,98.8 %,45.5 % and 20.8 % respectively compared with the control.In summary,the addition of biochar in phaeozem can effectively reduce the leaching of nutrients in the soil and improve the soil nutrient status;the addition of biochar in yellow soil can effectively reduce the leaching of DOC and nitrogen in soil,but promote the leaching of total phosphorus and total potassium.