Effects of Compost Application on Growth, Gas Exchange, and Green Yield of Cowpea [vigna Unguiculata (L.) Walp.] Varieties

Cowpea is an important dual-purpose legume grown for leaves, fresh pods, and grain, but its productivity in Ethiopia is limited by low-yielding varieties and poor soil fertility. This study evaluated the effects of compost application on growth, physiological traits, and yield of two cowpea varieties (Bole and Kenkety) during the main rainy season at Hawassa University, southern Ethiopia. Four compost rates (0, 2.5, 5.0, and 7.5 t ha⁻¹) were tested using a randomized complete block design with four replications. Compost application significantly (P < 0.05–0.001) increased plant height, leaf number, leaf area, leaf dry weight, photosynthesis, transpiration, pod traits, and green pod yield. Varietal differences were significant (P < 0.05) for growth, physiological traits, and pod characteristics. Significant compost × variety interactions affected shoot biomass, branch number, leaf fresh weight, and pod length. The highest plant height, leaf area, and photosynthesis rate were recorded at 7.5 t ha⁻¹ compost. The Bole variety combined with 7.5 t ha⁻¹ compost produced the highest biomass and pod length. Overall, compost at 7.5 t ha⁻¹, particularly with Bole, improved cowpea growth, physiology, and yield, demonstrating its potential as a sustainable soil fertility management option.