Abstract

The deep placement of nitrogen (N) fertilizer is considered as an effective strategy for crop growth and yield formation. However, it is unclear how deep N fertilizer placement under different rainfall levels might affect the nitrogen balance of winter wheat fields. Thus, we conducted a two-year field experiment in a semi-humid region to assess the effects of different N fertilizer placement depths of 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35) under three rainfall levels during winter wheat growth period (dry year = 125 mm, T1; normal year = 200 mm, T2; wet year = 275 mm, T3) on the N balance and crop productivity in winter wheat fields. Our results indicated that compared to D5, deeper N placement treatments increased the crop yield by 0.1–1.1 t ha–1 and N uptake by 3.0–18.0%, and reduced gaseous N losses by 0.2–1.1 kg N ha–1 under T1 and T2 (p < 0.05). T3D15 decreased the gaseous N losses by 1.2 kg N ha–1 compared with T3D5, and increased the yield and crop N uptake by 0.7–0.9 t ha–1 and 10.0–20.1 kg N ha–1 compared with T3D25 and T3D35, respectively (p < 0.05). T1 and T2 helped to maintain the N balance under deeper N placement (p < 0.05). Although T3 significantly increased NO3–-N concentration in the 60–100 cm soil layer and decreased the crop N uptake under D25 and D35, which was not conducive to maintaining the N balance, while D15 was beneficial in maintaining N balance (p < 0.05). Placement of N fertilizer at depths of 13.5 cm, 17.5 cm, and 21.6 cm in the wet year (T3), normal year (T2), and dry year (T1), respectively, could maintain the N balance in winter wheat fields through increasing crop N uptake, reducing gaseous N losses, and preserving the soil N pool.

Full Text
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