Bridging knowledge and good practices for enhancing soil fertility of mangrove swamp rice upland nurseries in Guinea‑Bissau through the use of compost

Nurseries established in the upland sandy soils are essential for Mangrove Swamp Rice (MSR) production in the Oio region of Guinea-Bissau. However, these soils are characterized by low levels of organic matter, exacerbating soil fertility constraints. With shorter rainfall seasons and accelerating organic matter mineralization, food insecurity is worsening, calling for collaborative solutions between farmers and researchers. Here, we researched the potential of using compost in improving soil fertility in MSR nurseries, addressing a knowledge gap about appropriate methods and respective outcomes for rice production in Guinea-Bissau. This transdisciplinary research was conducted in six villages and involved working collaboratively with a group of young farmers-researchers (YFR), who co-identified the problem, co-designed the trials and co-developed a composting technique tailored to the realities faced by MSR smallholders. Over 3 years, 16 composting piles were carried out using locally available raw organic materials and were co-evaluated for their quality. The produced composts were applied at two rates (1 kg/m2 and 2 kg/m2) across six nursery trials employing two experimental designs: the random distribution design (RDD) and linear distribution design (LDD). Soil properties – organic matter, nutrients, and plant growth parameters – were assessed. To evaluate field-level impact, seedlings from the different treatments were transplanted to MSR fields, where planting density and rice yields were quantified. Results demonstrated that compost application significantly improved nursery soil fertility and seedling quality, while reducing transplanted rice densities in MSR fields. Shorter nursery cycles and reduced pest incidence were also noted. The most effective compost application rate was 2 kg/m2, leading to optimized seedling production and increased rice yields. Beyond agronomic results, the study’s most important outcome was farmers’ acceptance and commitment to adopting and disseminating the technique. This underscores the value of co-innovation in advancing sustainable, locally adapted agroecological solutions in small-scale, low external-inputs Sub-Saharan African farming systems.