Effect of sulfonylurea herbicides residues on growth and yield of sunflower in rotation with wheat

To evaluate the effect of residue of sulfonylurea herbicides and  wheat residues on the growth and yield of sunflower, a split factorial experiment was conducted based on a randomized complete block design (RCBD) with four replications at the College of Agriculture, Shiraz University, Shiraz, Iran. The treatments included with and without wheat residues from the tested farm as the main plots, and a combination of three herbicides (Total, Apirus and Atlantis) and their concentrations (recommended and 30% overdose) which were considered as subplots. No herbicide treatment was used as control. The results showed that application of all herbicides reduced sunflower height, seed number and seed weight as well as seed yield of sunflower. The highest reduction in seed yield was recorded when Total  followed by Apirus residues were applied, which caused 95% and 80.6% yield reductions, respectively. Also, the minimum reduction of seed yield (32.7%) observed in Atlantis treatment. Moreover, 30% increase in herbicides dose caused increasing adverse effects and decreasing grain and biological yield compared to the recommended dose. Wheat residues incorporated to the soil increased damage of Atlantis by maintaining it in the soil (reduced seed yield from 3932.3 to 3556.9 kg/ha) and reduced damage of Total and Apirus by further degradation of these herbicides (increased seed yield from 235.4 to 311.6 kg/ha in Total treatment, and from 996.6 to 1161.3 kg/ha in Apirus treatment). But overall, wheat residues increased seed yield (2.1%) in comparison to the removal of plant residue. Therefore, addition of wheat residues as organic matter in the soil can affect the biological changes of herbicides.