Short-term effects of cowpea (Vigna Unguiculata [L.] Walp) cultivation and mineral fertilization on soil bacterial abundance and chemical properties

• This study evaluated the short-term effects of sole cowpea cropping with or without NPK fertilization on soil chemical and microbial properties. • Short-term sole cowpea cultivation significantly reduced available phosphorus and bacterial abundance, specifically in deeper soil horizons. • NPK fertilization partially mitigated microbial decline and nutrient depletion under monocropping conditions. • Soil depth showed a limited impact on microbial abundance and nutrient levels, except for minor variation in EC and potassium. • Findings support the recommendation of integrated nutrient management to maintain soil fertility in Sahelian agroecosystems. Cowpea (Vigna unguiculata [L.] Walp) is recognized for enhancing soil fertility through rhizosphere processes, yet its influence on bulk soil microbial and chemical properties remains poorly documented. This study assessed the short-term effects of sole cowpea cultivation, with and without mineral fertilization, on key indicators of soil fertility under Sahelian conditions. Specifically, it examined changes in soil chemical properties and bacterial abundance in response to these practices. Two field experiments were conducted during the 2021 and 2022 rainy seasons in Niger. Soil samples were collected before sowing and at harvest from three depths (0–10, 10–20, and 20–30 cm). Treatments included sole cowpea cropping and cowpea combined with an application of 100 kg ha - ¹ of NPK fertilizer 15-15-15. Chemical (pH, EC, extractable phosphorus, total nitrogen, potassium) and microbiological (bacterial abundance) parameters were analyzed. Soil depth had a limited influence on bacterial abundance and nutrient concentrations, with only minor depth-related variations observed in conductivity and potassium levels. However, sole cowpea cultivation significantly reduced available phosphorus (P = 0.0001) and bacterial abundance, specifically in the 20-30 cm depth, particularly during the 2022 season. The application of NPK partially mitigated these declines. Short-term cowpea monoculture may negatively affect microbial activity and accelerate phosphorus depletion in bulk soils, posing a potential risk to long-term soil fertility. The findings suggest that short-term monoculture of cowpea without balanced fertilization negatively impacts microbial biomass and accelerates nutrient depletion in bulk soil. Therefore, integrated nutrient management practices combining organic amendments, targeted mineral fertilization, and diversified cropping systems are recommended to enhance long-term soil health and resilience in Sahelian agricultural systems.