A field experiment was conducted twice at the farm of Environmental Studies and Research Institute, Sadat City University, Egypt, during the two consecutive seasons of 2015 and 2016 to study the effect of different additives of bentonite (0, 3, 6 and 9 t fed.-1), and microbial inoculation with Bradyrhizobium sp. and Azospirillum brasilense either alone or mixed on vegetative parameters, enzyme activity and yield of cowpea plants.
Results revealed that co-inoculation treatment and addition of 9 ton fed.-1 bentonite significantly enhanced plant height, number of branches, fresh and dry weight of plant in both seasons compared with the control at 60 days from sowing and this increase reflected on enzyme activity which attained 25.56, 27.66 (µmol/ C2H4/h/g dry nodules) and 50.93, 54.57 (µg TPF/g dry soil/h) for nitrogenase (N2-ase) and dehydrogenase (DHA) in the two growing seasons, respectively. On the other hand, the highest total seed yield of cowpea was recorded from use the co-inoculation with 9 ton ton/fed which was 0.679 and 0.682 (ton fed-1) for seed yield and 0.316, 0.324 (ton fed-1) for straw yield during 2015 and 2016 seasons, respectively.
Consequently, it is to recommend that mixture inoculate with Bradyrhizobium sp. and Azospirillum brasilense and addition of 9 ton fed.-1 bentonite could be improving crop growth of cowpea and improve sandy soil fertility.