Characteristics Of Nitrate Leaching And Model Simulation In Ridge-furrow Mulching Dryland

The arid agricultural area on the Loess Plateau is one of the most important grain producing areas in the region,but due to issues such as low annual rainfall and nitrogen deficiency,crop growth and yield are hindered.Mulching cultivation and nitrogen fertilizer input are important means of increasing agricultural production in the region.However,the extensive application of nitrogen fertilizer in the mulching system causes a large amount of nitrate residue in the soil profile,leading to negative environmental effects such as nitrogen leaching and greenhouse gas emissions.This study focuses on the dry land ridge and furrow covered corn system on the Loess Plateau.Five cultivation modes were selected:polyethylene plastic white film（M）,polyethylene plastic black film（M1）,biodegradable white film（MB）,biodegradable black film（M1B）,and open field cultivation（F）.Three nitrogen application measures were used:conventional urea（N1）,slow-release compound fertilizer（stanley N2）,and urea+dicyandiamide DCD（nitrification inhibitor N3）,Study the distribution,cumulative changes,leaching and yield characteristics of nitrate content in profiles under different treatments;Using the calibrated and validated Hydrus-2D model for scenario simulation,analyze the nitrate transport process and nitrate leaching flux characteristics of ridge covered corn soil under different rainfall intensities;To study the accumulation of soil nitrate in the root layer and leaching flux outside the root zone under the coupling effects of different fertilization and rainfall conditions,and to provide a basis for the regulation of soil nitrate leaching by the ridge planting and film covering corn system in the arid agricultural area of the Loess Plateau.The research results are as follows:（1）Ridge planting and film covering measures can increase nitrate residue in the 0-180cm profile,mainly in the 0-30cm surface soil.The open ground leveling treatment mainly remains in the 60-100cm soil layer.The residual nitrate levels in the surface layer of 0-30cm covered with plastic film in ridge and furrow cultivation were 5.89 times（2021 N1）,7.06-15.95 times（N2）,and 9.52-9.56 times（N3）higher than those in open field cultivation,respectively,while the residual nitrate levels in 30-180cm were significantly affected by interannual factors.Polyethylene plastic white film,black film,biodegradable white film,and black film are four types of film covering materials.Among them,biodegradable black film significantly increases the nitrate residue in the surface 0-30 cm and 0-180 cm profiles,increasing by 47%-615%and 38%-159%,respectively.The residual amount of the 0-180cm profile under the coverage of biodegradable film is higher than that under the corresponding polyethylene plastic film coverage.Compared with white film coverage,black film coverage significantly increased the accumulation of 0-30 cm soil layer.Under ridge cultivation with plastic film mulching,the application of slow-release composite fertilizer/urea+dicyandiamide can significantly increase the surface accumulation of 0-30 cm and significantly reduce the residual amount outside the root zone（120-180 cm）.Ridge raising and film covering measures are beneficial for increasing corn yield,and there is no significant difference in yield among different treatments under film covering.（2）The Hydrus-2D model can simulate the changes in soil water and nitrogen content under the ridge and furrow plastic film mulching corn system in the arid land of the Loess Plateau.The results show that the water simulation effect of the 0-180 cm profile is good,with R² ranging from 0.613 to 0.960.The fitting degree of nitrate nitrogen content changes in various soil layers of+10-10 and 60-100 cm under the ridge is relatively high,with R² ranging from 0.634 to 0.893.The simulation results of nitrate leaching process simulation under three rain intensities of moderate rain（15 mm）,heavy rain（35 mm）and rainstorm（65 mm）show that,with the increase of rainfall intensity,the depth of soil layer under leaching and infiltration continues to increase,the duration of leaching out of root zone is shortened,and the amount of leaching out of root zone is significantly increased.When the rainfall intensity is moderate rain,nitrate can slowly infiltrate into the soil layer at a depth of 120 cm;When the rainfall intensity is heavy rain,nitrate can leach and infiltrate into the 190 cm soil layer.On the 7th day after rainfall,the amount of nitrate nitrogen leaching is 0.19 kg ha^-1 day^-1;When the rainfall intensity reaches the rainstorm level,nitrate can leach to the soil layer below 200cm,and the nitrate nitrogen leaching loss on the seventh day reaches 0.28kg ha^-1 day^-1.（3）The accumulation and leaching of nitrate nitrogen in maize systems in arid areas of the Loess Plateau are mainly influenced by factors such as fertilization amount,rainfall,and film covering.Under ridge and furrow mulching cultivation and open field flat cultivation,with the increase of nitrogen application rate,the residual amount in the 0-180 cm profile,root layer accumulation,and leaching flux outside the root zone all increased;As the rainfall increases,the accumulated amount in the root layer gradually decreases,and the leaching flux outside the root zone gradually increases.The accumulated amount in the profile shows:R400（normal year）>R300（poor water year）>R500（high water year）.Compared with flat cropping cultivation in the open field,the nitrate accumulation in the 0-180cm profile in dry and normal years significantly decreased by 21.32%-24.53%;In humid years,it increased by 19.44%-22.11%.Compared with flat cultivation,when the rainfall is less than 450 mm,the accumulation of root layer in ridge cultivation with plastic film mulching significantly decreases,and the leaching flux outside the root zone increases,with an increase of 5.49%-25.88%;When the rainfall is greater than 450 mm,the cumulative amount of the root layer in ridge cultivation with plastic film mulching increased by 1.09%-50.52%,and the leaching flux outside the root zone decreased by 15.18%-22.95%.