Effects of marine purple bacterial fertilizer on mineralization, nitrous oxide emissions and broccoli yield

Agriculture relies heavily on inorganic nitrogen (N) fertilizers, excessive application of which contributes to greenhouse gas emissions. We explore a sustainable alternative, the lysed and dried biomass, namely, processed biomass (PB), from the marine purple non-sulfur photosynthetic bacterium Rhodovulum sulfidophilum , focusing on its N mineralization behavior, crop growth, and environmental impacts. Soil incubation experiments amended with PB at 10 °C, 20 °C, and 30 °C showed temperature-dependent N mineralization, with slower accumulation of ammonium nitrogen (NH 4 + -N) and delayed formation of nitrate nitrogen (NO 3 − -N) under a lower temperature. Across two seasons of broccoli field experiments (2023–2024), PB matched the performance of commercially available organic fertilizer (OF) and inorganic fertilizer (IF) in enhancing crop growth, yield, and soil fertility. PB exhibited a gradual N release of 68–72%, reflecting its slow-release nature, compared to 95–99% of rapid N release for IF over a period of 30 days. Application of PB at 1.5 times the standard N application rate (1.5N) reduced the nitrous oxide (N 2 O) emissions by 72.7 ± 18.7%, 58.5 ± 9.71%, 49.3 ± 5.30%, and 44.0 ± 1.94% on 3, 6, 12, and 19 days, respectively, compared with IF (1.5N). Similarly, when compared with IF applied at 1N, PB (1.5N) reduced N 2 O emissions by 41.5 ± 10.8%, 15.6 ± 6.60%, and 8.30 ± 3.54% on days 3, 6, and 12, respectively. These results demonstrate that PB can serve as an effective substitute for conventional fertilizers, contributing a slow-release, environmentally friendly N-source for sustainable vegetable production.