Investigation of Herbicide-Nitrogen Interaction on Wheat Yield and Yield Components in Competition with Lepyrodiclis holosteoides Fenzl.

To investigate interaction of herbicide and nitrogen on wheat and Lepyrodiclis (Lepyrodiclis holosteoides Fenzl.), a research was conducted at two different locations (Shahriyar and Karaj Regions) in RCBD with factorial arrangement and three replications. Research factors consisted of (i) Nitrogen application time (10 days before and 10 days after herbicide application), (ii) nitrogen rates (0, 30, 60 and 100% of the recommended dose, 150 kg ha-1 as urea source), and (iii) herbicide Sulfosulfuron 75% + Metsulfuron-methy 5% (Total®, UPL, India) rates (0, 30, 60 and 100% of the recommended dose, 40 g ha-1). Results obtained from the nitrogen-before-herbicide treatment indicated that when 150 kg ha-1 nitrogen was utilized before application of herbicide (less than 10 g ha-1), Lepyrodiclis seed No. increased up to 50000 m-2; however, an increase in the above herbicide dose (i.e. more than 10 g ha-1) had an adverse impact, that is to say, Lepyrodiclis seed No. drastically reduced. With application of nitrogen after herbicide utizilation (less than 10 g ha-1), it was found that Lepyrodiclis seed No. of both under study regions reduced. An increase in herbicide dose to more than 15 g ha-1 together with the increase of before-herbicide nitrogen application led to the reduction of Lepyrodiclis’ dry matter from 1200 to 300 g m-2. Increase of herbicide dose and also that of nitrogen applied before and after herbicide produced more wheat yield and yield components. An increase in nitrogen dose, particularly when it was applied after herbicide, aggravated herbicide efficacy in Lepyrodiclis control; the reason could be attributed to the nitrogen_herbicide interaction. Therefore, it could be concluded that benefiting from sufficient nitrogen and light, wheat produced more seed yield (6700 kg ha-1), compared to no-nitrogen/herbicide conditions (500 kg ha-1). Further, results revealed that an increase in nitrogen rate, particularly in that of after-herbicide application, left positive effect on herbicide efficacy in Lepyrodiclis control in a way that we achieved the goal (Lepyrodiclis control) with reduced herbicide dose.