Increased seasonal fallow intensity enhanced the soil fertility of latosol in a tropical multi-cropping region

Multi-cropping systems often supports sustainable crop production and increases soil degradation. Seasonal fallow is one of the key and commonly used agricultural practices for soil restoration in the tropics. Nevertheless, our knowledge of the impacts and mechanisms of seasonal fallow intensity on enhancing soil fertility remains poor. Here, we conducted a 6-year site-specific field trial in the latosol zone of a tropical monsoon climate characterized by high temperatures and rainfall. This study aimed to assess changes in soil fertility across a typical seasonal fallow intensity gradient (i.e., rice (Oryza sativa L.)-rice-bitter gourd (Momordica charantia L.), RRB; rice-bitter bourd, RB; fallow-bitter gourd, FB; green manure (sesbania (Sesbania cannabina (Retz.) Pers.))-bitter gourd, GB). The results showed that soil organic C, total N, and C- and N-acquiring enzyme activities at 0–40 cm increased with seasonal fallow intensity. Further, the characteristic regional microbial P limitation was partially alleviated by green manure, attributed to the incorporation of fresh organic matter. Regarding soil fertility, FB and GB were 25.8–34.0 % and 57.6–67.7 % higher in topsoil than RRB and RB, respectively, while GB in the subsoil (20–40 cm) was 22.2–37.1 % higher than other treatments. Specifically, seasonal fallow intensities benefit soil fertility by regulating soil C and N, available P, and acid phosphatase activity. Moreover, the positive correlation between bitter gourd yield and soil fertility confirms the improvement in soil fertility caused by seasonal fallow. In conclusion, intensifying seasonal fallow, especially by including green manure, effectively boosts soil fertility without compromising crop yield in tropical multi-cropping regions.