Increasing winter wheat yield and nitrogen utilization, and reducing residual soil nitrogen in semi-humid areas: A study matching deep fertilizer application with regional water scenarios

Abstract

The deep fertilizer application (DF) has been recommended as an effective strategy for promoting crop growth and yield formation. However, the controversial discussion revolves on the challenge of effectively using DF to simultaneously increase crop nitrogen (N) uptake and minimize residual nitrate contents to enhance N utilization efficiency. Based on a precipitation manipulation experiment conducted during 2019–2022 in a semi-humid area, we examined how annual precipitation amount during wheat growing season (125 mm = dry year; 200 mm = normal year; 275 mm = wet year) and the soil water storage before sowing (500 mm, SWSS500; 400 mm, SWSS400; 300 mm, SWSS300) variability affected the N uptake, N utilization efficiency, yield, and residual soil nitrate content in wheat fields treated with N fertilization at different depths (conventional surface fertilization depth of 5 cm: D5; 15 cm: D15; 25 cm: D25; 35 cm: D35). A complementary field experiment was also performed under natural rainfall condition using the 15N tracer technique to quantify the fate of fertilizer-N and 15N use efficiency (15NUE). 15N analyses showed that DF (D15, D25 and D35) significantly increased 15NUE by improving wheat 15N uptake (5.8–15.3%) and reducing potential 15N loss (9.6–12.3%) compared with D5, but the residual soil 15N in the 0–1.0 m layer increased (13.2–26.3%) as the fertilization depth increased (p < 0.05). The simulated precipitation experiment showed that compared with D5, DF significantly increased wheat N uptake, N utilization efficiency and yield by 1.4–16.4%, 1.4–14.0% and 3.3–21.5%, respectively, in the dry and normal years. In the wet year, N uptake, N utilization efficiency and yield under D15 increased by 1.9–9.8%, 2.1–11.1% and 2.2–13.4% compared to other fertilization depth treatments (p < 0.05). SWSS500 and SWSS400 significantly increased the N uptake (9.8–65.0%) and yield (0.6–69.3%) under all fertilization depth treatments irrespective of the annual precipitation amount than SWSS300 (p < 0.05). DF increased the residual NO3–-N concentration (0–2.0 m soil layer) by 2.2–7.3% compared to D5 across all annual precipitation amounts and SWSS levels, and D35 increased the maximum downward movement of NO3–-N to 1.4 m under wet year within SWSS500. DF at the depth of 14–20 cm effectively improved wheat N uptake and yield as well as minimizing the residual soil NO3–-N content. Applying moderate DF can enhance sustainable wheat production with high efficiency and yields in semi-humid regions.