Improving Nitrogen Management For Potato Production Basing On The Soil Ammonium Conversion In Northern Yinshan Area

Different crops had varying preferences for these nitrogen forms,which also fluctuated during their reproductive stages.Ammonium nitrogen and nitrate nitrogen are the main forms of nitrogen that plants can absorb and utilize.Accordingly,aligning the form of nitrogen supply with the specific demands of the crops was crucial for enhancing nitrogen utilization efficiency in crops.In China,the potato,a significant grain and vegetable crop,exhibited varying nitrogen form preferences before and after tuber formation.However,in potato cultivation,nitrogen fertilizer management often overlooked the specific nitrogen forms required,contributing to the crop’s low nitrogen utilization efficiency.Understanding the conversion of ammonium to nitrate nitrogen through soil nitrification was crucial,as it impacted the alignment between soil nitrogen supply patterns and potato demands.This knowledge was essential to enhance both potato yield and nitrogen utilization efficiency.This study conducted a systematic investigation into the transformation of ammonium nitrogen in soil over three years of field trials,focusing on the northern foothills of Yinshan Mountain in Inner Mongolia,a primary potato production region in China.Utilizing the principles of soil ammonia nitrogen transformation,this study refined the synchronization of nitrogen supply with potato demand through strategic timing of fertilizer application.It developed a nitrogen management model for optimization and further explored the viability of reducing nitrogen fertilizer in potato cultivation.The main findings were as follows:(1)In the primary potato production region at the northern base of Yinshan Mountain,the conversion rate of ammonium nitrogen to nitrate was 43% five days post basal fertilizer application,peaking at 95% on 19 d.During potato tuber formation and expansion,the conversion rate of ammonium nitrogen was 60%～68% respectively,five days following fertilizer application.These rates peaked at 97% ～98% on the ninth day.(2)Implemented a nitrogen fertilizer optimization scheme guided by the soil ammonium transformation law,specifically,applying nitrate before and ammonium after,with additional applications at 5 and 10-day intervals during potato tuber formation and expansion,significantly boosted the leaf area index and SPAD value in potatoes.This approach enhanced dry matter accumulation and nitrogen absorption in plants while reducing soil inorganic nitrogen levels,resulting in a 10-20% increase in potato yield and a13-29% improvement in nitrogen fertilizer utilization efficiency.Among the various approaches,the nitrogen fertilizer management program(N-D5),which involved a basal application of nitrate nitrogen fertilizer(30% of the total nitrogen)followed by ammonium nitrogen applications every 5 d,demonstrated the most effective results.(3)In the northern foothills of the Yinshan Mountains,a key potato production area,it is feasible to reduce nitrogen fertilizer by 10%(N-D5-10)based on the soil ammonium nitrogen conversion law,that is,the total nitrogen fertilizer is 270 kg/hm2,and it is feasible to apply ammonium nitrogen fertilizer at intervals of 5 days at intervals between the base application of nitrate nitrogen fertilizer(30% of the total nitrogen fertilizer),the tuber formation stage and the tuber expansion stage,respectively,which ensures the maximum yield of potato,significantly improves the nitrogen use efficiency,reduces the residue of inorganic nitrogen in the root soil,and reduces the environmental risk.