Combined effects of urea type and placement depth on grain yield, water productivity and nitrogen use efficiency of rain-fed spring maize in northern China

Abstract

Inappropriate nitrogen (N) application can lower N use efficiency (NUE) and crop water productivity (WP), and further affect the sustainable development of agriculture in the rain-fed areas of northern China. It is thus crucial to improve NUE and WP by developing a suitable nitrogen fertilization strategy. In this study, two urea types (UT), i.e., conventional urea (CU) and controlled-release urea (CRU), and three urea placement depths (PD) including 8 cm (D8), 16 cm (D16) and 24 cm (D24) were tested on rain-fed spring maize in 2017, 2018 and 2019. Grain yield (GY), partial factor productivity of N (PFPN), WP and nitrate N residue (NR) were evaluated. Compared with D8, D16 and D24 enhanced evapotranspiration, dry matter and N uptake of spring maize, and the increases were greater under CRU than CU. D16 produced the highest GY and WP among the placement depths, with mean values of 8417.8 kg ha−1 and 21.4 kg ha−1 mm−1, respectively. Compared with CU, CRU obtained higher mean GY (8754.5 vs. 7554.6 kg ha−1) and WP (21.8 vs. 20.2 kg ha−1 mm−1). The effects of UT × year and PD × year interactions on GY and WP were significant, indicating that these indicators had various responses to the planting year. The effects of UT × PD interaction on GY, WP and PFPN were not significant, suggesting that these indicators had similar responses to PD, independent of CRU or CU. CRU increased NR in the 0–80 cm soil profile, whereas it lowered NR in the 80–120 cm soil profile at harvest. Overall, the application of controlled-release urea at a placement depth of 16 cm achieved a better balance between agronomic and environmental benefits of rain-fed spring maize in northern China.