This study was conducted under controlled greenhouse conditions at the Atatürk University Plant Production Application and Research Center to determine the effects of different plant growth-promoting rhizobacteria (PGPR) strains on growth, yield, and forage quality of cowpea (Vigna unguiculata L. Walp.). The study compared the strains Serratia marcescens (PGB15), Pseudomonas chlororaphis (PGB43), Bacillus megaterium (PGB38), and Rhizobium sp. (FR28) with NPK fertilizer application. The experiment was arranged in a randomized complete block design with three replications, and growth, yield, and forage quality parameters were measured. The results showed that PGPR applications provided statistically significant increases (p<0.001) in all growth and yield parameters compared to both the control group and NPK fertilizer application. The strains FR28 and PGB15 increased key vegetative growth parameters such as plant height, root length, and leaf area by more than 50%, while FR28 showed the highest biomass production with increases of 105% and 214% in stem fresh and dry weight, respectively. In terms of forage quality, FR28 and PGB15 applications enhanced crude protein content, reduced NDF and ADF values, and increased relative feed value (RFV) to 263.09 and 250.19, respectively. Correlation analyses revealed strong positive relationships between crude protein content and biomass parameters, and strong negative correlations between NDF and ADF with quality parameters. Principal component analysis indicated that the first two components explained 96.54% of the variance, identifying FR28 and PGB15 as the most effective strains in terms of biomass production and forage quality. Based on these findings, it is recommended that FR28 and PGB15 strains be considered as promising biofertilizer candidates for practical use in cowpea cultivation, offering a sustainable alternative to chemical fertilizers.
Sedat SEVEROĞLU (Wed,) studied this question.