Research On Leaching And Transport Of Nitrogen In Five Typical Tobacco-growing Soils

At present,nitrogen is still the main factor affecting the yield and quality of flue-cured tobacco in the main producing areas of China,and the route,degree and influencing factors of nitrogen loss after application have not been fully identified.In order to reveal the main factors influencing the tobacco field soil nitrogen leaching and explore the migration rule of nitrogen in tobacco field soil,We use cinnamon soil,brown soil,purple soil,red soil,paddy soil as materials and investigate effects of combined application of rainfall,reduction fertilizer and biochar on the leaching of nitrogen in tobacco-growing soil by indoor soil column simulation.The solute transport model was used to simulate and predict the dynamic change of nitrogen leaching,and the law of nitrogen leaching in tobacco field was quantitatively described.The main conclusions were as follows:1.The cinnamon soil is an alkaline silty loam.The content of nitrate nitrogen is relatively rich,but the content of available phosphorus and potassium is relatively low.The brown soil is a weakly acidic loam and a relatively rich potassium content.The contents of nitrate nitrogen,ammonium nitrogen and available phosphorus that can be absorbed by plants in the soil are relatively low.The red soil is an acidic loam clay.The contents of total nitrogen,available potassium and available phosphorus are relatively rich,but the contents of nitrate nitrogen,ammonium nitrogen and organic matter are relatively low.The purple soil is an acidic loam clay.The contents of total nitrogen,available potassium and available phosphorus are relatively rich,but the contents of organic matter,nitrate nitrogen and ammonium nitrogen are less.Paddy soil is a neutral loamy clay.The contents of nitrate nitrogen and organic matter in the soil are relatively rich,but the available phosphorus in the soil is relatively short.2.In the whole process of leaching,leaching of nitrogen mainly in leaching appears the first five times,and the inorganic nitrogen in the form of nitrate nitrogen leaching,and ammonium nitrogen leaching amount are much lower than the nitrate nitrogen,nitrate nitrogen loss between 24 mg to 98 mg.After reduced fertilization,the cumulative leaching of nitrogen in tobacco field was 6%～37%lower than that under conventional fertilization.Compared with conventional fertilization,reduction fertilizer+biochar could significantly slow cinnamon soil,red soil,purple soil nitrogen leaching time,and for brown soil and paddy soil did not delay the time of its nitrogen leaching appear,at the same time reduce weight+biochar early treatment can significantly reduce the leaching of nitrogen leaching,The cumulative amount of leaching decreased by up to 65%during the whole leaching process.In most tobacco fields,the leaching rate of nitrate nitrogen increased after the application of inorganic nitrogen fertilizer,while the leaching rate of soluble organic nitrogen decreased.However,the leaching rate of nitrate nitrogen could be significantly reduced by reducing fertilization and adding biochar,up to 22%.3.The leaching of soluble organic nitrogen in cinnamon soil was greatly affected by rainfall intensity,while the leaching of ammonium nitrogen and nitrate nitrogen was less affected by rainfall intensity.Although the leaching amount of different nitrogen forms in red soil was not significantly affected by different rainfall intensity,the leaching amount of different nitrogen forms was 18%～30%higher when the rainfall intensity was higher than when the rainfall loudness was lower.The leaching of nitrogen in brown soil,purple soil and paddy soil showed a decreasing trend,and the early eluting was greatly affected by the intensity,and the effect of rainfall intensity weakened with the decrease of leaching amount in the middle and late leaching period.The overall leaching amount of heavy rain intensity was always higher than that of light rain intensity.4.The OSM model coupled with Freundlich adsorption can better simulate the transport of ¹⁵NO₃^-at the flow rate of V2 and V3,R²>0.95.OSM model can accurately simulate the penetration time of¹⁵NO₃^-and the trend of concentration over time.The soil resistance to the transport of ¹⁵NO₃^-under the three flow rates is V1>V2>V3.Using HYDRUS-1D to simulate the outflow concentration change of¹⁵NO₃^-at a soil thickness of 40cm,the outflow curve obtained is smooth.It is found that the ¹⁵NO₃-in deep soil requires a longer time,and the chemical reaction on the transport of ¹⁵NO₃^-is also not considered.The impact of shifting needs to be further explored.