Grain Sorghum Response to NPK Fertilizer in the Guinea Savanna of Ghana

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is an important food crop grown by subsistence farmers in Africa with little or no fertilizer. Field experiments were conducted in 2002 and 2003 on sandy loam soil in Guinea savanna of Ghana to determine the agronomic and economic benefits of applying nitrogen (N), phosphorus (P), and potassium (K) fertilizers to sorghum. Four N levels (0, 40, 80, and 120 kg⁻¹ as urea) were combined with two P levels (0 and 17.2 kg P ha⁻¹ as triple superphosphate) and two K levels (0 and 33.3 kg K ha⁻¹ as muriate of potash) to constitute 16 treatments that were tested in a randomized complete-block design with three replications. Fertilizer N, P, and K did not show significant interactions for any parameter. Across years, added K did not influence grain yield and yield components. However, P increased yield by 14%, and N affected yield in a quadratic manner. The application of 40, 80, and 120 kg N ha⁻¹ resulted in yield increases of 47%, 60% and 69% over farmers' practice (0 kg N ha⁻¹), respectively. Economic analysis revealed that two N and P combinations, i.e., 40:0 and 40:17.2 kg ha⁻¹, were economically superior and stable within a price variability range of 20%. Thus, farmers in the Guinea savanna agro-ecology in Africa can get better returns on the money invested in fertilizer for producing improved sorghum than with their traditional practice of no fertilizer input.

Keywords:

• Sorghum bicolor
• nitrogen-use efficiency
• economic response
• grain yield
• semi-arid

Acknowledgments

We appreciate the support provided by the Agricultural Services Sub-Sector Investment Program (AgSSIP) through SARI that partially funded this study. We also thank all the technical staff of SARI, Wa station, who assisted in data collection.