Understanding farm-level diversity to guide soil fertility management in West African cotton systems: Evidence from Benin

Although cotton cultivation grants farmers access to annual inputs of mineral fertilisers, there is a generalised tendency of soil fertility decline in Benin's cotton-growing area. This study aimed to understand the link between farm socioeconomic diversity, soil management practices, and soil fertility status in cotton-based farming system of Benin. Socio-demographic and farm management data were collected from 242 farms on three sites in southern-central and northern Benin. Principal component analysis and a hierarchical clustering were used to construct a farm typology. Soil management practices were analysed in the light of this typology. Composite soil samples 20 cm deep were then taken from 40 plots representing the farm/soil types identified, to assess variability in soil fertility as influenced by farm types and management practices. Four farm types emerged, differing in resource endowments and soil management practices. Practices such as manure application (92 %) and rotational herd corralling (42 %) were adopted more often by livestock owners. Farms without livestock implemented practices such as crop rotation (90 %) and intercropping (41 %). Soil fertility status was low to very low in all farms sampled across the three sites (extractable phosphorus <10 mg P/kg soil, soil organic matter < 20 g kg−1 soil). Although a link between farms' soil management practices and soil fertility status was expected, no statistical differences were detected across farm types (p > 0.05). Cotton yields, as declared by farmers, were also not statistically associated with soil fertility levels. The generalized poor fertility status of soils that receive annual fertilizer inputs suggests that this practice is not enough to maintain long-term soil productivity in the climatic and soil conditions of Benin cotton zones studied here. This was also the case in fields that received combinations of mineral fertiliser and animal manure, which is probably not used in sufficient quantity and quality. Low organic matter inputs, crop residue removal and conventional tillage, as practiced by the majority of farmers in our study sites (100 %), may contribute to explain the low levels of SOM and organically-held nutrients in the soil. Alternative measures to maintain soil fertility should be further investigated locally for their capacity to restore and maintain soil fertility in the long term and to improve crop yields, considering the socioeconomic diversity of farms and their environment.