Effects Of Subsoiling Tillage And Straw Turning And Burying Back To The Field On The Distribution Of Fertilizer Nitrogen In Soil And Plant

Adequate nitrogen supply is a necessary condition for high yield of crops.Excessive nitrogen application not only causes resource waste,but also causes soil and groundwater environmental pollution.Reasonable water and nitrogen management measures have an important guiding role in the protection of farmland ecological environment safety.In recent years,with the application of various machinery and unreasonable farming measures in farmland soil cultivation,the soil plow bottom has become thicker and hardened,and the soil plow layer has become shallower,which has become more and more serious.Too thick and hard plough bottom will cause the root system of crops to be unable to penetrate deeply,and the crops will not be able to use the nutrients in the deep soil.Different farming methods such as subsoiling and long-term straw turning and burying back to the field can improve the situation.In order to explore the retention,transformation and plant absorption of chemical fertilizer nitrogen after being applied to the soil.This experiment is based on the long-term positioning experiment of Gongzhuling Jilin province black soil as a platform.Three types of tillage treatments were set,namely Rotary tillage（XG）,long-term Subsoiling tillage（SS）and long-term straw turning and burying back to the field（JG）.The study uses the ¹⁵N tracer technique in field micro-plot experiments to clarify the characteristics of accumulation and vertical transport of fertilizer nitrogen in soil profile,accumulation in different organs of plants,grain size distribution and ¹⁵N abundance of soil aggregates in mature soil after maize growth period.In order to clarify the occurrence and transformation in soil aggregates with different grain sizes were systematically studied,and then the position and function of urea nitrogen in nitrogen migration under different tillage methods and the effect of Nitrogen Migration on soil structure stability were accurately quantified.1.Long-term straw turning and burying back to the field（JG）can increase the total nitrogen content and fertilizer nitrogen accumulation in the soil at different layers.Compared with the XG treatment,the total nitrogen content of the JG treatment in the 15-20 cm layers of the four growth periods of maize increased by14.55%～26.24%,and the increase was the largest in the jointing stage.In the seedling stage,chemical fertilizer nitrogen was mainly accumulated in the 15-20cm layer,and the residual rate of ¹⁵N fertilizer in the soil of different treatments was19.13%-26.94%.Fertilizer nitrogen was mainly accumulated in the 0-15cm soil layer at the jointing stage,tasseling stage and maturity of corn,and the residual rates of ¹⁵N fertilizer in the soil layer were 18.64%-29.46%,9.02%-14.57%,4.98%-10.77%,respectively.The average nitrogen densities of the three tillage treatments XG,SS and JG were 11.91,11.73 and 13.76 t hm^-2during the maize growth period.Long-term Subsoiling tillage（SS）and long-term straw turning and burying back to the field（JG）can increase the content of macro-aggregates（>0.25mm）in soils at different levels and improve the stability of aggregates.Subsoiling tillage（SS）and straw turning and burying back to the field（JG）can improve the distribution ratio of fertilizer nitrogen to macro-aggregates in the 0-15cm,15-20cm,20-30cm and 30-50cm soil layers,and the straw burial effect is better.2.Subsoiling tillage（SS）and straw turning and burying back to the field（JG）can promote the accumulation of mineral nitrogen in the soil at the seedling and jointing stages of maize,increase the content of total NH₄⁺-N and NO₃^--N and the content of NH₄⁺-N and NO₃^--N from fertilizer nitrogen sources.The proportion of NO₃^--N from fertilizer nitrogen sources in the total soil NO₃^--N was significantly higher than that of NH₄⁺-N from fertilizer nitrogen sources in the total NH₄⁺-N in the soil.The contribution of fertilizer-derived mineral nitrogen to total soil mineral nitrogen in the15-20cm soil layer was higher than that in the 0-15cm soil layer.More than 95%of the mineral nitrogen remained in the form of NO₃^--N in the soil profile at the maturity stage of maize.At the same time,subsoiling tillage and straw turning and burying back to the field can reduce the transformation of fertilizer nitrogen to mineral nitrogen in deep soil（70-100cm）and reduce the risk of nitrogen leaching.3.Fertilizer nitrogen mainly accumulated in the grain and leaves of maize plants,followed by stems.The combination of SS and JG treatments with an appropriate amount of nitrogen fertilizer could promote the uptake of nitrogen by maize reproductive organs,and the crop yield was increased by 17.18%and 28.03%,respectively,compared with the XG treatment.Under XG,SS and JG tillage treatments,the nitrogen use efficiency of crops were 25.89%、34.77%、41.56%.In summary,long-term subsoiling and straw burial treatment can coordinate the properties in the soil,increase the good structure and microbial content in the soil,increase the nutrient content in the soil,promote chemical fertilizer nitrogen fixation and transformation in soil,improve plant nitrogen use efficiency and yield,reduce the loss of various forms of nitrogen.