Technical Approaches for Enhancing Rice Yield and Nitrogen Use Efficiency with Sulfur-Coated Controlled-Release Fertilizers

Sulfur-coated slow-release fertilizers comprise four nitrogen (N) products with distinct release periods. This study aimed to determine whether these products should be applied individually or in combination, whether they should be blended with quick-release N fertilizers, and how to optimize their application to synergistically improve rice yield and nitrogen use efficiency (NUE).

The field experiments were conducted in Yangzhou and Changzhou, Jiangsu Province from 2022 to 2024, using rice cultivars Nanjing 9108 and Nanjing 46 as test materials. The trials included comparisons of slow-release N products, screening of optimal product combinations, evaluations of fertilizer types, blending ratios of slow- and quick-release N fertilizers, and application timing of quick-release N, and optimization of slow-release N formulations. The effects of sulfur-coated slow-release fertilizer application methods on rice yield formation and nitrogen uptake and utilization were analyzed。

(1) The rice yield under the straw return treatment increased by 4.50% and 8.88% compared with the half-straw return and no-straw return treatments, respectively. Additionally, the nitrogen use efficiency (NUE) under the straw return treatment was 11.35% and 25.64% higher than that under the other two treatments, respectively. (2) The rice yield of the 60-day slow-release nitrogen product was 4.10%, 15.68%, and 19.09% higher than that of the 30-day, 90-day, and 120-day products, respectively, but 4.13% lower than that of the conventional precise fertilization. Overall, the NUE of the 60-day product exceeded that of other slow-release nitrogen products by an average of 8.68%. Under no-straw return and half-straw return conditions, the NUE was 9.88% and 0.93% higher than that under conventional precise fertilization, respectively; however, under full straw return, it was 4.57% lower. (3) The combination of slow-release nitrogen products in the ratio of 3+6+9 achieved the highest rice yield and NUE, yet both were lower than those of the conventional precise fertilization. (4) The treatment with a blending ratio of 7:3 (slow- to quick-release nitrogen) achieved the highest rice yield, nitrogen accumulation, and NUE, averaging 4.31%, 3.25%, and 6.15% higher than that under conventional precise fertilization, respectively. Under this treatment, applying quick-release fertilizer as tillering fertilizer (for medium-duration varieties) or panicle initiation fertilizer (for long-duration varieties) synergistically improved yield, nitrogen accumulation, and NUE. The yield increase was primarily attributed to a significant enhancement in spikelets per panicle on the basis of adequate panicle number. (5) When slow-release nitrogen products were blended at a ratio of 30-day:60-day:90-day = 1:4:1, rice yield, nitrogen accumulation, and NUE all achieved the highest values, averaging 3.76%, 5.66% and13.35% higher than conventional precise fertilization, respectively, which was closely associated with significant increases in leaf area index (LAI), sink capacity, and biomass yield.

A blended slow-release N fertilizer was formulated by combining three controlled-release fertilizer with dissolution periods of 30 d, 60 d, and 90 d at a 1:4:1 mass ratio. Application of this blended slow-release N with quick-release N at a 7:3 ratio—implemented through one-time basal application of slow-release fertilizer and single topdressing of quick-release N as either tillering fertilizer (for 150-day varieties) or flowering-promoting fertilizer (for >160-day varieties)—significantly increased grain yield by 3.76% and nitrogen use efficiency by 13.55% compared with conventional precision quantification. This field-validated protocol demonstrates sulfur-coated fertilizers enabled synergistic gains in rice productivity and nitrogen utilization efficiency.