Studying the sensitivity of cotton and maize to simulated imazthapyr herbicide residue

To evaluate the soil residue of imazthapyr effects on cotton and maize, an experiment was carried out based on completely randomized design at greenhouse of Agricultural Faculty of University of Gonbad Kavous. Different doses of imazthapyr (0, 4.5, 23, 45, 68, 91, 140, 180, 230, 340 and 450 μg.kg-1 soil) were applied on maize and cotton and finally the dry weight of root and shoot, shoot height, root length and leaf area of crops were measured. Three and four Log- logistic curves were fitted to the data. Results indicated that almost all data fitted better to the three parameter log- logistic curve. Results of separate fitting of the data showed that the residue of imazthapyr always reduced dry weight of crops. For 50 percent reduction of shoot dry weight of cotton and maize, 13.26 and 21.91 g.a.i.ha-1of imazthapyr were needed respectively. To reduce 50 percent of root dry weight of cotton and maize, 72.75 and 25.19 g.a.i. ha-1of imazyhapyr were needed. Generally, the results of data simultaneously fitting showed that maize root and shoot sensitivity to imazthapyr were always more than cotton. Shoot height, root length and leaf area were decreased as imazthapyr residue was increased.