Objectives The combined application of organic and inorganic fertilizers represents a well-established strategy for enhancing both the yield and N use efficiency in the greenhouse vegetables systems. Nevertheless, the fate of N derived from organic fertilizers, specifically its partitioning and stabilization among different soil organic matter fractions, remains inadequately characterized. This knowledge gap constrains a mechanistic understanding of the synergistic effects underlying combined organic-inorganic N management. To address this, we conducted an in situ microplot experiment using swine manure, with the objective of elucidating the distribution patterns of organic fertilizer, derived N within particulate organic matter (POM) and mineral-associated-organic matter (MAOM) in greenhouse soils. Our findings are expected to inform precision fertilization strategies for optimizing combined organic and inorganic N application in greenhouse vegetable systems.

Methods Based on a 16-year greenhouse vegetable (cucumber-tomato rotation) long-term experiment at the National Agricultural Science Observation Station in Shijiazhuang, Hebei Province, three treatments were established: chemical N fertilizer alone (C¹⁵N), 50% chemical N + 50% swine manure N with ¹⁵N-labeled urea (M¹⁵N), and 50% chemical N + 50% pig manure N with ¹⁵N-labeled pig manure (¹⁵MN). The ¹⁵N isotope tracer technique combined with physical particulate fractionation was used to analyze soil physicochemical properties, carbon and N contents, ¹⁵N atom percent excess, and ¹⁵N recovery in POM and MAOM fractions under different fertilization managements.

Results Compared with CN, the MN significantly decreased soil EC and nitrate in 0-20 cm topsoil by 64.0% and 41.1%, respectively, while increasing available phosphorus by 137%. It also significantly increased soil organic carbon content in both POM and MAOM fractions across the 0-60 cm soil profile. The ¹⁵N recoveries in POM and MAOM under ¹⁵MN were 24.3% and 20.0%, respectively, significantly higher than those under M¹⁵N and C¹⁵N treatments in the 0-20 cm layer. In the 0-60 cm soil profile, the total ¹⁵N recoveries in POM and MAOM under ¹⁵MN were 59.0% and 43.9%, respectively, compared to only 9.3% and 2.5% under ¹⁵N. Notably, the total ¹⁵N recovery in the 0-60 cm soil profile under ¹⁵MN reached 103%, much higher than that under M¹⁵N (45.0%) and C¹⁵N (11.8%) treatments.

Conclusions Under the same total N input level, swine manure-derived organic N could could decrease the NO₃^--N content in 0−20 cm soil layer, increase the organic N partition and content in POM and MAOM greatly, and with even more higher values in 20−40 cm soil layer, thereby significantly enhance the retention efficiency of greenhouse soil nitrogen, reducing potential N losses effectively.