Effects of Type and Application Rate of Some Widely-Used Pesticides on Growth and Biological Nitrogen Fixation in Soybean

This experiment was carried out to evaluate the effects of some widely-used pesticides in Golestan province on the growth and biological nitrogen fixation (BNF) in soybean (Glycine max (L.) Merr.). Pot experiment consisted of 10 pesticides, two pesticide application rates (recommended and twice recommended rate) and 2 soybean cultivars (a determinate and an indeterminate). A factorial arrangement at a randomized complete block design with 8 replications was used. Results showed that the effects of three factors on total dry weight (TDW), leaf dry weight (LDW), nitrogen (N%), protein (P%), total nitrogen (TN), and BNF per plant were significant (P=0.01). Pesticide kind and application rate had significant interactions on evaluated traits. Based on findings, pesticides used in this study can be divided into three groups; a) Super gallant (a post-emergence herbicide) and Admiral (an insecticide) that had no significant effects on BNF and TN even when applied in twice recommended rate, b) Basagran (post-emergence herbicide), Dursban (insecticide), Omite and Neorun (acaricides) that had no significant effect on BNF and TN when used in recommended rate, but their effects on BNF and TN were significant when applied in twice recommended rate, c) Two pre-plant herbicides (Treflan and Sonalan), a post-emergence herbicide (Fusilade) and a acari- insecticide (Novacron) that had significant effects on BNF and TN independent of application rate. These findings emphasize the importance of selected pesticide kind and application rate. Also, TDW, LDW, TN and BNF in indeterminate cultivar (Williams) was significantly more than determinate cultivar (Sahar).