Nitrogen accumulation and nitrogen substitution effect of maize under straw returning with continuous cropping

: Crop straw resources in Northeast China are rich, but burning and discarding are serious, and nutrient utilization rate is very low. We explored the feasibility of the substitution of straw returning to nitrogen fertilizer and its effects on nitrogen accumulation under continuous cropping in cold region. A frame culture and continuous positioning experiment was carried out in the experimental site of Northeast Agricultural University from 2017 to 2019, with 15 N labeled urea. A three-factor split-plot design was adopted in this experiment, the main plot was straw returning method with no straw returning (S0) and straw returning (S1), and the sub-plot was nitrogen application levels with 0 (N0), 175 (N1), and 350 (N2) kg hm –2 . Two application methods were set for each fertilizer application amount, one ratio of base fertilizer and top dressing applied was 1:1, and the other ratio of base fertilizer and top dressing applied was 1:0. The results were as follows: When the straw returning amount was 12 t hm –2 , the returning straw could replace 36.8 kg hm –2 pure nitrogen. The average amount of maize straw was 46.50 million tons in Heilongjiang Province from 2017 to 2019, and straw returning could replace 142,700 tons pure nitrogen. The replace amount of pure nitrogen in the ratio of base fertilizer and top dressing (1:1) was 26.88% higher than that in 1:0. Straw returning was negatively correlated with nitrogen use efficiency in maize. The average nitrogen use efficiency of maize in S0 treatment was 6.09% higher than S1 treatment, and the yield of S1 treatment was 4.66% higher than S0 treatment when the urea application amount was 350 kg hm –2 (161 kg hm –2 pure nitrogen). The highest yield of maize was 268.22 g frame –1 in the treatment of straw returning and topdressing with commonly fertilizer applied in local agriculture. In conclusion, the nitrogen substitution effect was remarkable under maize straw returning in Northeast China. Long-term combined application of crop straw and nitrogen fertilizer significantly improved the biomass, yield, and nitrogen accumulation of maize, which was a cultivation mode for increasing yield and efficiency of maize in Northeast China.