EVALUATING THE EFFECT OF ROCK PHOSPHATE AND TRIPLE SUPERPHOSPHATE SUBSTITUTION AND OTHER NUTRIENTS ON COWPEA PERFORMANCE IN GHANA’S GUINEA SAVANNA AGROECOLOGY

Abstract

Cowpea (Vigna unguiculata L. Walp) is a crucial legume crop in Ghana, contributing significantly to food security due to its nutritional and economic value. However, productivity is hindered by low soil fertility, mainly phosphorus depletion and insufficient micronutrient use, particularly zinc and boron. The study evaluated cowpea’s response to Triple Super Phosphate (TSP) and its substituted forms for Rock Phosphate (RP) in combination with potassium and micronutrients (Zn and B) in phosphorus- depleted lixisols at Nyankpala and Kokpeng in Northern Ghana. The treatments including three OCP compound fertilizers, were 16 and were laid out using randomized complete block design with 4 replications. The results, indicated significant effects (P < 0.05) of fertilizer treatments on growth parameters measured, chlorophyll content, root characteristics and grain yield. Notably, compound fertilizers with micronutrients NKP (14:18:18) + TE and NPS (14:31:5) + TE improved root length and nutrient uptake efficiency. Optimal grain yields (over 2,500 kg/ha in Nyankpala) were achieved with specific combinations of TSP and RP, particularly in 80% TSP + 20% RP + K + TE and 60% TSP + 40% RP + K + TE treatments. The study also found that 100% RP + K + TE outperformed 100% TSP in grain yield, indicating the efficiency of RP combined with K and the micronutrients. Economic analysis revealed that 100% RP gave a favourable marginal rate of return of 475%. Integrating phosphorus sources with K, Zn, and B can significantly enhance crop growth, improve root development, and increase grain yield in the Guinea Savanna agroecological zone. The study recommends the use of Zn, B, and rock phosphate as a cheaper P source in place of TSP for improved cowpea growth and yield. Further research on the use of rock phosphate should be conducted in Northern Ghana.