An Optimized Nitrogen Application Rate and Basal Topdressing Ratio Improves Yield, Quality, and Water- and N-use Efficiencies for Forage Maize (Zea mays L.)

Abstract

Applying nitrogen (N) fertilizer at irrational rates and basal topdressing ratios typically leads to high resource wastage and serious environmental pollution and is a global problem. A pot experiment was conducted between 2020 and 2021 to investigate the effects of different N application rates and basal topdressing ratios on the growth, yield, quality, and water- and N- use efficiencies of forage maize. Four N treatments were used, with the following levels: 0 kg/ha (N0), 70 kg/ha (N70), 140 kg/ha (N140), and 210 kg/ha (N210); and two basal topdressing ratios of N fertilizer were tested, namely: 2:8 and 4:6. An increased N application rate, from 0 to 200 kg/ha, increased whole fresh and dry yields. N fertilization increased the crude protein (CP) content of different plant parts (stems, leaves, and ears), as well as at the whole plant level, but decreased neutral and acid detergent fiber content. The dry matter water use efficiency (WUEDM) increased, while the partial-factor productivity of applied N decreased with an increasing N application rate. Compared with N0, the 2-year average dry matter yield under N70, N140, and N210 increased by 21.8%, 27.6%, and 38.2%, respectively, while WUEDM increased by 19.1%, 28.7%, and 45.0%, respectively. At the 2:8 basal topdressing ratio, the dry matter yield, CP content, and N recovery efficiency under all N application rates were higher at harvest compared to the 4:6 ratio during normal rainfall years, while dry matter yield and WUEDM were both lower compared to the 4:6 ratio during dry years. In conclusion, during a normal rainfall year, a N application rate of 210 kg/ha, with a basal topdressing ratio of 2:8 between the sowing and jointing stages, is considered the optimal N fertilizer application strategy to improve forage maize production in the semi-arid areas of the Chinese Loess Plateau.