Effects Of Different Fertilization Measures On Ammonium Lattice Fixation Potential In Farmland Black Soil

The application of nitrogen fertilizer plays an important role in the development of agricultural production and the improvement of grain yield.In agricultural ecosystems,understanding the fate and transformation of fertilizer nitrogen in soil is a key scientific issue in regulating and improving crop nitrogen utilization.Therefore,this study used the long-term positioning test base for black soil fertilizers in Gongzhuling City,Jilin Province as the research platform,and selected four fertilization treatments(CK,no fertilization;NPK,fertilizer;M1NPK,fertilizer with low organic fertilizer;M2NPK,fertilizer with high organic fertilizer)to explore the effects of different fertilization modes on the total nitrogen and fixed ammonium content of different soil layers,as well as the maximum fixation capacity of soil in different soil layers under different fertilization treatments.At the same time,the dynamic changes in fixed ammonium and mineral nitrogen content were studied under different nitrogen application levels and their combinations with nitrification inhibitors without crop absorption and utilization.The 15 N isotope tracing technology was used to reveal the distribution and transformation of fertilizer nitrogen to fixed ammonium reservoirs at different cultivation periods,effectively elucidating the role of fixed ammonium in soil nitrogen retention and supply processes.The relevant conclusions are as follows:(1)The results of field in situ experiments showed that the total nitrogen and fixed ammonium contents of each fertilization treatment showed a gradually decreasing trend with the deepening of the profile.Long term application of chemical fertilizers significantly increased the fixed ammonium content in the0-20 cm soil layer,with an increase of 14.94 mg/kg.The combination of chemical fertilizers and low amount organic fertilizers significantly increased the fixed ammonium content in the 0-20 cm and 20-40 cm soil layers,with an increase of36.59mg/kg and 13.7mg/kg.The combination of chemical fertilizers and high amounts of organic fertilizers can significantly increase the fixed ammonium content throughout the entire 1m soil layer,with an increase of 53.22mg/kg,29.12mg/kg,10.69mg/kg,12.8mg/kg,and 7.822mg/kg,respectively.The relative content of fixed ammonium in different soil layers under different fertilization treatments is over10% of total nitrogen in the soil,especially in deep soil,where its contribution rate to total nitrogen is higher.Compared with the no-fertilization treatment,the long-term application of chemical fertilizers increased the maximum ammonium fixation capacity of the soil,while the combination of chemical fertilizers and organic fertilizers reduced the maximum ammonium fixation capacity of the soil.(2)The indoor incubation experiment showed that the fertilizer nitrogen fixed by clay minerals was a long-term effective nitrogen pool.Under different fertilization modes,the content of fixed ammonium increased with the increase of nitrogen application rate,and the higher the nitrogen application rate,the more significant the increase.The application of nitrification inhibitor promoted the fixation of ammonium by clay minerals by inhibiting soil nitrification at different stages of the experiment,and the inhibition effect of the inhibitor was more significant with the increase of nitrogen application.(3)Under different nitrogen application levels,the conversion amount and proportion of fertilizer nitrogen to fixed ammonium storage vary among the four fertilization modes.As the nitrogen application level increases,the conversion proportion increases more.Nitrification inhibitors are beneficial for improving the role of fixed ammonium in nitrogen retention and supply,and the effect is more obvious at high nitrogen application levels.Under the same nitrogen application rate,the conversion amount and proportion of fertilizer nitrogen to fixed ammonium storage were significantly lower in the treatment of chemical fertilizer and organic fertilizer combination than in the treatment of no fertilization,and the low amount organic fertilizer treatment was higher than the high amount organic fertilizer treatment.When the nitrogen application rate is 250 kg N/ha,it can not only increase the fixed ammonium content in the soil,but also maintain a high level of fertilizer nitrogen conversion to fixed ammonium and the conversion ratio.At the same time,it can reduce nitrogen loss during the cultivation process,which is conducive to building a soil nitrogen literacy pool and improving the efficient utilization of fertilizer nitrogen.It should be recommended as a nitrogen application rate for farmland soil.