Realizing the efficiency of the “4R” fertilization principle by using controlled-release and stable nitrogen fertilizers in soybean production in Northeast China

Objectives This study aimed to evaluate the application methods of controlled-release urea (CRU) and stabilized nitrogen fertilizer (SF) in combination with the “4R” fertilization principle on soybean production through field experiments, in order to provide a scientific basis for the efficient use of new-type fertilizers.

Methods Field experiments were conducted at Minzhu Experiment Base of Heilongjiang Academy of Agricultural Sciences from 2023 to 2024. In 2023, the treatments included conventional fertilization (FP, farmers’ practice), recommended fertilization (NE, recommendation by the Nutrient Expert system), CRU at shallow application of 6−8 cm (CRU8) and deep application of 13−15 cm (CRU15), and SF at shallow application of 6−8 cm (SF8) and deep application of 13−15 cm (SF15). In 2024, the two shallow application treatments were replaced by deep application under reducing 20% of N input (CRU80%, and SF 80%), NE treatment was split into no-N control (CK) and NE, making seven treatments in total. Plant biomass and N accumulation, soil mineral N, and field N accumulative release rate of CRU during soybean growth period were analyzed; soybean yield, economic benefit, and N use efficiency (NUE) were calculated at harvest stage.

Results CRU released 42.1% and 83.0% of its total N within 37 and 67 days after application to soil, respectively, with the release process occurring 15−35 days earlier than the corresponding soybean N uptake. In 2024, the soil NO₃⁻-N and NH₄⁺-N content in CRU and SF treatments were lower than in NE and FP at the seedling stage, but they kept increasing gradually and reached peaks at the podding stage annd flowering stage, respectively; while the soil NO₃⁻-N and NH₄⁺-N in NE and FP treatments start to decrease gradually with the growth period. The soil NO₃⁻-N and NH₄⁺-N in CRU80% and SF80% were lower than those in CRU and SF treatments at most of growing stages. The total fertilizer inputs in NE, CRU, and SF treatments were the same, which were 46.1% less than FP treatment, so the fertilizer costs were reduced by 473−549 yuan/hm². As the seed yields of NE, CRU, SF, and CRU80% were similar with FP, the net profit increased 614−1692 yuan/hm², and SF exhibited significantly higher net profit. The nitrogen agronomic efficiency was the highest in SF, followed by CRU and CRU80%, which were significantly higher than NE, and CRU80% achieved the highest N use efficiency.

Conclusions Fertilization based on the “4R” principle (NE) effectively improved soybean yield and nitrogen use efficiency compared with farmers’ practice. Replacing urea with controlled-release or stable nitrogen fertilizer through one-time basal-application at 15 cm depth beside the soybean roots better matched soil inorganic N supply with crop N demand throughout the entire growth period of soybean, and achieved comparable soybean yield and fertilizer efficiency. Moreover, CRU allowed a further 20% N reduction without yield loss while enhancing NUE. Therefore, one-time deep application of controlled-release or stabilized N fertilizers is an effective strategy for simplifying fertilization and improving efficiency in soybean production in Northeast China.