The Effect of Different Levels of Humic Acid Fertilizer on Components of Biological Nitrogen Fixation in Cowpea Cultivars in Ahvaz

Abstract

Making use of humic acid in agriculture due to different physiological effects not only increases the yield but also decreases the consumption of chemical fertilizers and reduces environment pollution. Humic acid is among the substances which have dual effect on biological nitrogen fixation, i.e. it can develop the roots and has positive effect on activity of soil microorganisms and can increase biological nitrogen fixation in legumes. In order to study the effect of different levels of humic acid on components of biological nitrogen fixation in cowpea cultivars a factorial experiment in the form of randomized complete block design was carried out in Ahvaz in 2011. Three levels of humic acid (H1 = 0, H2 = 75 PPM, H3 = 150 PPM) and two cowpea varieties (V1 = local, V2 = Egyptian) were placed in plots as a combination. Humic acid was once sprayed to crops at the end of vegetative growth. The results showed that humic acid foliar spray fertilizer significantly increased root growth, number of roots, and number of nodules, root dry weight, and nitrogen percentage of crop nodule. The highest percentage of nitrogen fixation belonged to H3 treatment by 6.10%. Moreover, the effect of cowpea cultivar on all traits was significant except on the number of roots and the length of pod. The highest percentage of nitrogen fixation belonged to Egyptian cultivar by 5.81%. In this experiment, Egyptian cultivar was more efficient than local cultivar.