Effects Of Biochar On Water Infiltration And Nitrogen Leaching In Grassed Loess Soils

Prevention and control of nitrogen leaching in the Loess Plateau is of great significance to ecological environment protection and sustainable economic development.In this study,a soil column simulation test was used,with bare soil+0%biochar as the control(CK),to investigate the effects of ryegrass+0%biochar(C1),+1%biochar(C3),+2%biochar(C4)and 3%biochar(C5)and tall fescue+0%biochar(C2),+1%biochar(C6),+2%biochar(C7)and 3%biochar(C8)on loess soil infiltration,simultaneously study the horizontal(nitrogen leaching experiment on different days)and vertical(the same leaching experiment with different sampling times)leaching and loss of nitrogen(total nitrogen,nitrate nitrogen and ammonia nitrogen)in CK-C8 treatments at two stages(basic fertilizer and topdressing).The main research conclusions are as follows:(1)There was no significant difference in the effect of CK-C8 treatments on the infiltration process at the initial stage of infiltration.Plant root growth and biochar effect may affect soil properties,thereby changing the process of soil infiltration.Compared with CK,C1-C8 treatments inhibits the migration of wet front and reduces soil infiltration performance.C8 treatment has the strongest inhibitory effect on soil infiltration.The soil infiltration performance of tall fescue is weaker than that of ryegrass.The higher the amount of biochar added under the two grasses,the weaker the soil infiltration performance.The infiltration process of different treatments conformed to the Kostiakov,Philip and Horton infiltration models(R~2≥0.991).Both grasses and biochar in the first stage can reduce the loss rate of leaching solution,and the loss rate is negatively correlated with the amount of biochar added,which is consistent with the infiltration process.(2)The horizontal and vertical changes of total nitrogen concentration in the two stages are different.In the first stage,(longitudinal)the total nitrogen concentration of CK-C8treatments in the first six trials decreased with the leaching time,and the seventh and eighth trials showed a stable trend;while the concentration(horizontal)decreased first and then stabilized with the increase in the number of leaching.In the second phase,(longitudinal)the total nitrogen concentration of the CK-C8 treatments in the first seven trials showed a steady trend with the leaching time,the eighth and ninth trials showed an increasing trend,and the tenth and eleventh trials showed a decreasing trend;and the concentration(horizontal)with the increase of leaching times first stabilizes,then rises and then falls.The change pattern of nitrate nitrogen concentration is similar to that of total nitrogen.(3)The adsorption or absorption of nitrogen by biochar and grass affects the leaching loss of total nitrogen and nitrate nitrogen.In the first stage leaching test,C1-C8 treatments inhibited the leaching loss of total nitrogen and nitrate nitrogen compared with CK,and the difference between the two grasses under 0%biochar was not significant.Under different grasses,1%,2%and 3%biochar treatments inhibited total nitrogen and nitrate leaching compared with 0%biochar treatments.There is no obvious relationship between the amount of biochar added under different grasses and the total leaching loss of total nitrogen,but it is negatively correlated with the total leaching loss of nitrate nitrogen.The second phase of the leaching test has poor regularity,which may be caused by changes in soil structure and nitrogen content due to grass-planting causing surface crusts,root development and biochar desorption.Biochar itself may contain a large amount of nitrogen,leading to the risk of promoting total nitrogen leaching due to high addition.In the seventh and eighth trials of the first stage and the first five trials of the second stage,the total nitrogen leaching loss of 2%and 3%biochar treatments was higher than that of bare soil.(4)The leaching loss of ammonia nitrogen is significantly lower than that of total nitrogen and nitrate nitrogen,and the difference in regularity between the two stages is relatively small.The ammonia nitrogen concentration of CK-C8 treatments in each test of the two phases(longitudinal)showed a gentle trend or fluctuating change with the leaching time.In the first stage,the ammonia nitrogen concentration(horizontal)of the C4,C5,C7,and C8 treatments decreased with the increase of the number of leaching and then leveled off,the rest of the treatments all showed a steady trend.The concentration of ammonia nitrogen(horizontal)in the second stage fluctuates slightly with the increase of leaching times.Compared with CK,C1 treatment(two stages)and C2 treatment(first stage)reduced the total ammonia nitrogen leaching loss.The three types of biochar treatments under the two stages of different grasses all promoted ammonia nitrogen leaching compared with 0%biochar.And the promotion effect increases with the increase of the amount of biochar.(5)Nitrate nitrogen was the main form of leaching in the two stages.The proportion of nitrate nitrogen in CK,C1 and C2 was all higher than 85%,while the proportion of nitrate nitrogen in C3,C4,C6 and C7 was more than 80%,and that in C5 and C8 was more than47%.The maximum ratio of ammonia nitrogen(3%biochar)is not more than 20%,among which CK-C3 and C6 treatments are less than 5%.Grass had no obvious effect on the form of nitrogen leaching.Biochar decreased the ratio of nitrate nitrogen and increased the ratio of ammonia nitrogen,and the higher the addition amount of biochar,the lower the ratio of nitrate nitrogen and the higher the ratio of ammonia nitrogen.