Objectives The application pattern of controlled-release urea affects the grain-filling and yield components of wheat. This study used Richards model to simulate the filling process of winter wheat under different fertilization patterns, and proposed the appropriate fertilization modes and blending ratios.

Methods Field experiments were conducted in Guanzhong area of Shaanxi, using winter wheat ‘Xiaoyan 22’ as tested crop and a controlled-release urea with 180-days releasing period as tested fertilizer. The three blending ratios of controlled-release urea to common urea were 8∶2 (N2), 7∶3 (N3) and 6∶4 (N4). The two fertilization patterns were once basal applying of all blended fertilizers (referred to basal application, B), and basal applying controlled-release urea and topdressing common urea at jointing stage of wheat (referred to topdressing, T). No N fertilization (CK0), pure common urea applied in ratio of basal and topdressing of 4∶6 (CK1), and pure controlled-release urea once basal applied (CK2) were the three controls. The tiller number was investigated at tillering and reviving stage, the yield components were investigated at harvest. The first grain sample collection was conducted on the 5th day after the end of flowering, then repeated in 5 days intervals and 9 collection in all, and the 1000-grain weight was calculated. Taking sampling days after flowering as independent variable (t) and the corresponding 1000-grain weight as dependent variable (W), the grain-filling parametersand growth potential were calculated using formula W = A/(1 + Be^ - Kt)^1/E .

Results N fertilizer significantly increased the 1000-gain weight and yield of the wheat. Topdressing of N fertilizer increased photosynthetic products, the higher the proportion of top-dressed N, the greater the initial growth potential was. Appropriate topdressing ratio prolonged the duration of the filling period, with the longest extension of 11.83 days, and reached the maximum filling rate earlier, with the earliest of 3.791 days. All the treatments reached the maximum growth potential in the fast increase period (P_w2), topdressing treatments increased both the duration and growth rate of the fast increase (P_w2) and slow increase periods (P_w3), compared with the basal treatments. The duration was extended by 1.28–2.27 days in T2 and 4.46–7.49 days in T3, respectively, and the growth potentials increased by 4.69%–7.80% (P_w2) and 20.12%–37.25% (P_w3). Basal treatments significantly increased the number of tillers and effective panicles than topdressing did, with averaged increases of 204.1–264.0 and 29.0–97.1 No./m², respectively. Fertilization methods and blending ratios showed significant interaction on effective ear rate and yield, among all the treatments, TN2 and BN3 achieved the highest yields. TN2 also produced the largest 1000-grain weight (41.32 g), and BN3 had the most effective panicle number (546.5 panicles/m²).

Conclusions Fertilization patterns and blending ratio of controlled release urea with common urea effectively regulate the filling process and yield formation. Using the controlled-release urea with 180 days releasing period, mixing controlled-release urea with common urea in 7∶3 and applied once as basal (BN3), or in ratio of 8∶2 and topdressed urea (TN2) all perform well. BN3 is effective in producing higher tiller number and effective ear number, increasing the maximum filling rate and delaying the appearance of the maximum growth rate. TN2 does well mainly by keeping longer and higher filling rate and growth potential. Considering the labor cost in topdressing, BN3 is preferred to TN2, while for higher 1000-grain weight, TN2 is preferred in the tested area.