Nitrogen uptake of soybean and soil nitrate nitrogen under long-term rotation and different fertilization in a brown soil of northeast China

Objectives Based on a long-term fertilization experiment in a brown soil of northeast China, the effects of different fertilization on soybean biomass, grain yield and nitrate N residual in 0–100 cm soil layer were systematically studied in a corn-corn-soybean rotation system. The results would provide theoretical basis and scientific instruction for crop rational application of fertilizer in rotation system.

Methods A long-term field experiment was initiated in 1979 in brown soil in Liaoning Province. The fertilization treatments included: no fertilizer (CK), N fertilizer alone (N), combined application of N, P and K chemical fertilizers (NPK), manure at low rate (M₁), M₁ combined with N (M₁N) or NPK(M₁NPK), manure at high rate (M₂) and M₂ combined with chemical N (M₂N)or NPK (M₂NPK). The manure was applied only in corn season since 1992. The soybean biomass, yield, N uptake were measured at harvest, and the soil nitrate N residual in 0–100 cm soil layer was determined before seeding and after harvest of soybean in 2018.

Results The soybean biomass, grain yield and N uptake in treatments of M₁, M₁N, M₁NPK, M₂, M₂N and M₂NPK were significantly higher than those in CK and N. Among all the treatments, the highest soybean biomass, grain yield and total N uptake were all appeared in M₁NPK, which were 9107 kg/hm², 2979 kg/hm², and 314.2 kg/hm², respectively, and were 6.1%–133.6%, 23.9%–232.5% and 11.7%–359.4% higher than those in the other treatments. The highest N harvest index was found in NPK and M₁NPK, which was 63.5%. However, the N physiological efficiency in NPK and M₁NPK were 30.6% and 28.1% lower than that in CK, respectively. Compared with the soil nitrate N before sowing, the soil nitrate N in 0–100 cm layer at harvest was increased significantly in N treatment, did not change significantly in NPK, while reduced significantly in low rate manure treatments, the reduce percentages in M₁ treatments were averaged by 79.2%. At harvest, the lowest nitrate N accumulation in 0–100 cm soil was in M₁NPK, which was 58.2% lower than those in all the other treatments on average.

Conclusions In the corn-corn-soybean rotation system of northeastern China, the combined application of NPK fertilizer with 13.5 t/hm² of manure in corn season and application of NPK fertilizer alone in soybean season can increase the nitrogen efficiency of the following soybean, increase its grain yield, and reduce the soil nitrate N residue significantly, which is a suitable fertilization method for this crop rotation system.