Optimizing NPS fertilizer application to enhance productivity of maize–bean intercropping on Ferralsols

Abstract Maize ( Zea mays L.) and common bean ( Phaseolus vulgaris L.) are major food crops that support smallholder farming systems, yet productivity remains low on Ferralsols due to nutrient limitations and low input use. Ferralsols are characterized by acidity, low cation exchange capacity, and limited availability of nitrogen, phosphorus, and sulphur, which constrains crop growth and yield. This study evaluated the effects of NPS (12–45–5, Zn 0.2%) fertilizer on growth, yield, and nutrient use efficiency of maize–bean intercropping on Ferralsols in the Eastern Agro-ecological Zone of Tanzania during the 2024/2025 short rainy season. The experiment was arranged in a randomized complete block design with three replications and fifteen treatments, combining sole maize, sole common bean, and maize–bean intercropping with seven NPS rates (0–180 kg ha −1 ). NPS fertilizer was applied to maize in sole and intercropped systems, while sole common bean received no fertilizer, reflecting its capacity for biological nitrogen fixation. Increasing NPS rates significantly improved vegetative growth and yield of maize and enhanced vegetative performance of common bean through indirect soil nutrient effects in intercropping. Maize grain yield increased from 2.0–2.3 t ha −1 in unfertilized treatments to 3.4–3.7 t ha −1 at 120–150 kg ha −1 NPS, with smaller gains at 180 kg ha −1 . Nutrient use and recovery efficiencies declined at higher rates, indicating diminishing returns. Application rates of 120–150 kg ha −1 NPS balanced yield improvement and input efficiency, supporting targeted fertilizer recommendations for maize–bean intercropping on Ferralsols in tropical smallholder systems.