Objectives It is hypothesized that micronized organic fertilizers can improve nutrient supply intensity and pool size. We verified this hypothesis to develop a sustainable fertilization strategy that synergistically reduces fertilizer use and enhances use efficiency in chili cultivation.

Methods A field experiment was conducted over two consecutive years (2023–2024) in Quzhou City, Zhejiang Province, with chili pepper (Capsicum annuum L.) as the test crop. Under conditions of identical basal application rates of compound fertilizer and drip irrigation, two fertilization treatments were established: conventional water-soluble fertilizer (DF) and micronized organic fertilizer substituting 30% of the conventional water-soluble fertilizer (DFM). A non-topdressing control (CK) was also included. Ammonia volatilization fluxes throughout the entire growth period of the chili pepper were measured using the closed static chamber air extraction method. Plant growth parameters, fruit yield and quality, and surface soil fertility were systematically investigated.

Results Compared with the DF treatment, the DFM treatment simultaneously promoted dry matter accumulation in both shoot and root systems during the early growth stage of chili pepper, as well as leaf area expansion. At the early fruiting stage, the dry matter weights of stems-leaves and roots increased by 35.6% and 39.8%, respectively, while the leaf area index (LAI) rose by 9%. Over the two-year trial, the DFM treatment resulted in an average increase of 21% in fruit dry weight and total yield, a 9% increase in N accumulation in fruits, and a 10% increase in single-fruit weight. Regarding soil fertility, the DFM treatment significantly enhanced the contents of total organic carbon (TOC), dissolved organic carbon (DOC), alkali-hydrolyzable nitrogen, and available potassium in the topsoil layer. However, there was no significant difference in cumulative ammonia volatilization losses between the DFM and DF treatments, although both were significantly higher than those of the CK.

Conclusions In drip-irrigated chili pepper production, substituting 30% of conventional chemical fertilizer with micronized organic fertilizer optimizes vegetative growth and dry matter accumulation during the early growth stage, promotes N uptake and accumulation in plants, particularly in fruits, thereby significantly increasing yield and improving the visual quality of the fruits. This fertilization regime also effectively enhances topsoil organic carbon and available N and K contents, but fails to concurrently reduce cumulative ammonia volatilization losses. This phenomenon indicates the high lability of N in the micnonized organic fertilizer. Further research is warranted to determine the optimal substitution ratio of micronized organic fertilizer for water-soluble fertilizer and to refine the total nitrogen input rate.