Objectives Application of nitrogen (N) fertilizer inhibitors has become an important strategy for increasing the yield and quality of peaches. This study aimed to investigate the effects of combined application of nitrification and urease inhibitors on soil nitrogen transformation in peach orchards, and to evaluate their efficacy in improving peach yield and fruit quality.

Methods A soil incubation experiment was firstly carried out to investigate the effects of nitrification inhibitor (DMPP) and urease inhibitor (NBPT) on inorganic N content and apparent nitrification rate from the peach orchard soil in Pinggu, Beijing. The soil incubation experiment included 5 treatments: no urea amendment (CK)‌, ‌urea alone (U)‌, ‌urea combined with DMPP (U+DMPP)‌, ‌urea combined with NBPT (U+NBPT)‌, and ‌urea combined with both DMPP and NBPT (U+DMPP+NBPT)‌. The soil inorganic nitrogen concentrations were regularly tested during the 60-day incubation period. Subsequently, a two-year peach field experiment was conducted in Pinggu of Beijing from 2023 to 2024. Four treatments were setup, including fruit swelling fertilizer alone (CF), and fruit swelling fertilizer (PGF) combined with DMPP, NBPT, and both, respectively. The peach yield, quality, and soil inorganic nitrogen concentrations were measured at harvest of peaches.

Results In the soil incubation experiment, DMPP significantly inhibited the conversion of NH₄⁺-N to NO₃⁻-N. On the third day of incubation, the NH₄⁺-N content reached its peak and maintained higher levels throughout the entire cultivation process, compared with U treatment, leading to reduced soil apparent nitrification rate; U+NBPT treatment delayed the hydrolysis of urea in orchard soil until 12 days, the NH₄⁺-N content reached its peak on the 15th day, and was recorded significantly higher apparent nitrification rate of soil in the early stage of cultivation, relative to U treatment. In the later stage, U+NBPT treatment was recorded lower soil NH₄⁺-N content, and higher soil apparent nitrification rate, relative to that of U+DMPP treatment. In 2023, the PGF+DMPP treatment produced a peach yield of 45.7 t/hm², the yield was 11.2% higher, and the single fruit weight was 9.2% higher than that of CF, respectively. In 2024, the peach yield was 65.8 t/hm², with a yield increase of 18.2%, and a single fruit weight elevation of 17.6%. The effects of PGF+NBPT or PGF+DMPP + NBPT treatments in increasing fruit yield and individual fruit weight were not as good as those of PGF+DMPP treatment. In 2023 and 2024, PGF+DMPP increased the longitudinal diameter of peaches by 4.6% and 6.8%, the vitamin C content of peaches by 76.3% in 2023, and the transverse diameter of peaches in 2024 by 5.6%, compared with the CF treatment, the soluble solid content of peaches in the PGF+DMPP+NBPT treatment increased by 27.9% and 26.5% respectively. The PGF+DMPP treatment significantly increased the hardness of peaches by 22.2% in 2023.

Conclusions Application of DMPP kept a relatively high soil NH₄⁺-N level through inhibiting its transformation to nitrate nitrogen, co-application of fruit swelling fertilizer with DMPP outperformed co-applicaton with NBPT or DMPP and NBPT in the peach yield and quality improvement, so DMPP is recommended for the peach production and quality in Pinggu, Beijing.