Optimum basal and topdressing ratios of nitrogen fertilizer for strong and medium gluten wheat cultivars

Objectives Studies on grain protein content, nitrogen (N) use efficiency, and wheat yield under different basal and topdressing ratios of N fertilizer have laid the theoretical basis for improved N-use by wheat in the Heilonggang basin, Hebei Province.

Methods Two-year field experiment was conducted with two wheat cultivars (Jimai 22 and Gaoyou 2018). No nitrogen fertilizer (N₀) was designated as the control. Under the same rate of N application, four N treatments with a basal topdressing ratio of 3∶7 (N_3:7), 4∶6 (N_4:6), 5∶5 (N_5:5) and 6∶4 (N_6:4) were set. Nitrogen topdressing was carried out with irrigation at the jointing stage. We analyzed the dry matter and N accumulation during the wheat main growing period, grain total protein content and various protein components, nitrogen efficiency and grain yield in the two wheat cultivars.

Results Dry matter and N accumulated quantities in the two wheat cultivars increased at first and then decreased with increasing N basal topdressing ratio. As the growth period advanced, plant dry matter accumulation rate in the two wheat cultivars increased and then decreased. Similarly, the N accumulation rate showed an increase-decrease-increase trend. The stage from jointing to flagging was the main period for wheat dry matter and N accumulation. At maturity, the dry matter and N accumulation were higher in N_4:6 and N_5:5 than in other treatments in Gaoyou 2018 and Jimai 22. N_4:6 in Gaoyou 2018 had higher grain albumin, globulin and glutenin contents than other treatments, increasing total grain protein by 3.66%–10.76% and grain yield was 1.07–1.13 times of other treatments. Further, it increased the N partial productivity, N recovery rate, and agronomic efficiency. N_5:5 in Jimai 22 increased albumin by 2.55%–4.78%, globulin by 4.11%–16.92%, gliadin by 3.42%–10.39%, glutenin by 1.35%–10.32%, and total protein content by 2.95%–10.06%. The grain yield was 1.03–1.08 times of other N treatments, significantly increasing the N recovery rate. The N accumulation rate from flagging to maturation stage in Gaoyou 2018 was relatively higher than Jimai 22; grain protein components of Gaoyou 2018 were 1.17%–5.72% higher than Jimai 22. In contrast, the grain yield in Jimai 22 was 5.4%–15.21% higher than in Gaoyou 2018.

Conclusions The basal to dressing ratio of nitrogen fertilizer that meets the N accumulation characteristics of wheat is conducive to high wheat yield and quality. The N accumulation rate of medium gluten wheat cultivar decreased from flagging to maturation stage, and the basal topdressing ratio of N fertilizer was 5∶5. In contrast, the N accumulation rate of strong gluten wheat cultivar was high from flagging to maturation stage. The basal topdressing ratio of N fertilizer is increased to 4∶6, which potentially enhances high yield and grain protein content in wheat.