Effects of Combined Maize Straw Turnover and N Application on Nitrogen Absorption Characteristic and Yield of Winter Wheat

The effects of the combination of returned straw and different N fertilizer application rates on the characteristics of nitrogen absorption and utilization in winter wheat and its grain yields in lime concretion black soil were systematically studied,based on the data from a five year experiment in Mengcheng City,Anhui Province.Field trials were carried out to investigate the changes of wheat yield,the nitrogen content and absorption intensity of wheat plant,as well as nitrogen use efficiencies,and to examine the optimum nitrogen application rate under straw turnover conditions in lime concretion black soil.The results showed that wheat yield where maize straw was turnover for five years decreased by 4.1%~46.1% in the early two years,but increased by 5.7%~12.8% after the fourth year,especially combined with nitrogen application rate of 243.0kg N·hm-2.Under the combination of straw turnover with low(162.0~202.5kg N·hm-2)and excess amount(324.0kg N·hm-2)of nitrogen application rates treatments,a single peak curve appeared in the plant nitro-gen content,which occurred at jointing,anthesis and booting,respectively.While with the nitrogen application rates of 243.0~283.5kg N·hm-2 treatments,the peaks of plant nitrogen content occurred at wintering and during jointing to booting stages.Wheat nitrogen absorption intensity was increased with the increase of nitrogen fertilizer amount,but low amount of nitrogen fertilizer could result in early senescence of wheat at late growth stages.For straw turnover and applying nitrogen fertilizer,the suitable plant nitrogen content for the highest wheat yield of 9 860kg·hm-2 were 3.12%~4.72%,with peaks appeared at jointing and booting stage.Nitrogen agronomy efficiency,nitrogen absorption utilization efficiency in plant aboveground and grain were significantly decreased with increase of nitrogen application rate,and the nitrogen harvest indexes of treatments with nitrogen application were significant higher than that without nitrogen application.In general,the suitable nitrogen application rate under the maize straw turnover for winter wheat was 243 kg N·hm-2,and a greater yield effect could be achieved after 4 continuous years of straw turnover.