Declining soil fertility remains a major constraint to vegetable production in tropical regions, necessitating sustainable and efficient nutrient management strategies. This study evaluated the effects of biochar, cow manure and their co-application on growth, yield and soil chemical properties of spinach (Spinacia oleracea L.) under field conditions in western Uganda. A field experiment conducted in 2025 tested four treatments: control, biochar alone (50 t ha−1), cow manure (20 t ha−1), and co-application of biochar (25 t ha−1) and cow manure (10 t ha−1), arranged in a Randomized Complete Block Design (RCBD). Results indicate that the co-application of biochar and manure produced the tallest plants (45.6 cm), approximately 120% taller than the control (20.7 cm), and increased plant height by 35.7% compared to biochar alone. Similarly, the highest yield (22.5 t ha−1) was obtained under the co-application of biochar and manure. Specifically, the co-application of biochar and manure significantly increased spinach yield by 78% compared to biochar alone, while a non-significant increase of 31.1% was observed relative to manure alone. Furthermore, principal component analysis (PCA) revealed strong positive associations among growth and yield parameters and soil total N, K, EC and pH. Overall, the co-application of biochar and manure enhanced spinach productivity and soil fertility in tropical systems.
Wacal et al. (Mon,) studied this question.