Quantitative Relationship And Its Mechanism Of Nitrogen Use Efficiency And Soil Fertility In Black Soil Region Of Northeast China

Nitrogen(N)is one of the essential macronutrients for crop growth.Application of nitrogen fertilizer is the main measure to maintain high and stable yield for crop production.But it resulted in lower nitrogen use efficiency(NUE)and serious environmental problems with excessive application rate of nitrogen fertilizer.It was an urgent task to improve NUE in China.Black soil is the main producing area of maize in China,and different soil fertility has formed by continuous long-term different fertilization treatments.Determining the relationship between NUE of maize and soil fertility,and the difference of nitrogen mineralization of different fertility soils is essential for guiding N application,enhancing NUE of maize and decreasing nitrogen fertilizer losses.Based on the long-term field experiments in black soils,five soils were collected with great difference in soil fertility,and five different rates of N were applied for each soil using 15 N isotope pot experiments with maize.Maize yield,N uptake and NUE of maize were measured;soil nitrogen mineralization was also investigated under three different incubation temperature(15,25 and 35 ℃)at the same time.The main results are as follows:1)There was a significant positive correlation between maize yield and soil Integrated Fertility Index(IFI)and nitrogen application ratio(NR).We can describe the quantitative relationship using the following equation:Yield=6037+4210×NR+4908×IFI(R2=0.694,P<0.001).2)There was a significant positive correlation between 15NUE of maize and soil Integrated Fertility Index(IFI),but significant negative correlation between 15NUE and nitrogen application ratio(NR).We can describe the quantitative relationship using the following equation:15NUE=44.77+5.88×IFI-7.02×NR(R2=0.7036,P<0.5).3)Under the same incubation temperature,soil nitrogen mineralization increased with improvement of soil fertility.For example,the potential of nitrogen mineralization of the five soils were 215.16,243.00,245.12,304.54 and 305.75 kg/ha,respectively,when the incubation temperature was 35 ℃.The dynamic process of nitrogen mineralization is consistent with the dynamic process of nitrogen accumulation in maize,and the higher the soil fertility,the higher the matching between these two processes.According to the quantitative relationship of maize yield and NUE with IFI and NR,we analyzed the relative contribution ratio of soil fertility and nitrogen application rate,and the result showed that it is the primary task to improve the soil fertility to obtain high yield and NUE of maize.