Effect of imazaquin applications on the growth, leaf chlorophyll and yieldof soybean in the guinea savanna of Nigeria

Field trials were conducted during the wet seasons of 1989, 1991, 1994 and 1995 to evaluate the effects of pre-emergence and post-emergence applicatio ns of four rates of imazaquin (0.00; 0.15; 0.30 and 0.45kg a.i/ha) on the g rowth, leaf chlorophyll types and grain yield of soybean c.v. SAMSOY 2. Ima zaquin applications had no significant effect on the growth of soybean root s on most of the sampling dates, but pre-and post-emergence applications of imazaquin at 0.30 and 0.45kg a.i/ha reduced soybean root nodules at 5 and 7 weeks after planting (WAP). Soybean shoot growth was generally reduced at SWAP by the pre-emergence and at 7WAP by the higher rates (0.30 & 0.45kg a .i/ha) of post-emergence application of imazaquin. Pre-and post-emergence a pplications of imazaquin showed a strong tendency to reduce the concentrati on of chlorophyll a and total chlorophyll at at 3 and SWAP respectively. Th e concentrations of chlorophyll types in soybean leaves at 9WAP was general ly comparable among most treatments especially in 1991. Whole plant fresh w eight of soybean at 7WAP was reduced by all rates of post-emergence applica tion of imazaquin. However, there was no significant difference in the whol e plant dry weight of soybean at 3 to 7 WAP in 1989 and at 3, 5 and 9WAP in 1991. In each trial, pre-and postemergence applications of soybean signifi cantly increased the grain yield of soybean compared with the control treat ment. This study showed that, inhibition of soybean shoot growth and leaf c hlorophyll concentration was transient and that soybean plants require abou t 6 weeks for complete recovery from imazaquin phytotoxicity.