Effect of split nitrogen fertilization and herbicide application on soil weed seed bank in wheat (Triticum aestivum L.) and oilseed rape (Brassica napus L.) rotation

Abstract

In order to investigate the effects of nitrogen splitting and herbicide application on soil weed seed bank in a wheat and oilseed rape rotation, a field experiment was conducted in research station of the School of Agriculture, Shiraz University, Iran in 2005-6 and 2006-7. Results suggested that at 304 kg urea ha-1 when half of it was applied through sowing stage of wheat and oilseed rape and the other half applied at tillering stage of wheat and the end of rosette stage of oilseed rape grain and biological yield enhanced substantially in wheat and oilseed rape. Presence of weeds in weedy checks plot increased biological yield 57% in wheat, 142% in oilseed rape. On the other hand, it reduced wheat grain yield 53% and oilseed rape grain yield 65% comparing with weed free plots. Results indicate that herbicides application enhanced grain yield 88% in wheat, 63% in oilseed rape. However, it decreased weeds’ dry weight 58% in wheat and 78% in oilseed rape when it compared with weedy checks plot. Furthermore, iodosulfuron–methyl– sodium plus mesosulfuron–methyl–sodium in wheat reduced the annual rising of the soil weed seed bank 53% in 0-15cm and 71% in 15-30cm depth, while haloxyfop-(R)-methylester in oilseed rape decreased it 43% in 0-15cm and 40% in 15-30cm depth.