Effects of Nitrogen and Rapeseed Residues on Grain Yield and Yield Components of Sunflower (Helianthus annuus L.) and Weed Growth

ABSTRACT- Crop residue is applied to amend soil properties and increase crop yield. In this study, the effects of rapeseed residues and different rates of nitrogen on grain yield and yield components of sunflower and weed dry matter were investigated. The experiment was conducted at the Experimental Farm of College of Agriculture, Shiraz University, located at Badjgah, Shiraz, Iran in ۲۰۰۷-۲۰۰۸ and ۲۰۰۸-۲۰۰۹ growing seasons. Treatments were nitrogen levels (۱۵۰, ۳۰۰ and ۴۵۰ kg urea ha-۱) as main plot and rates of residue rapeseed (۲۵%, ۵۰%, ۷۵%) and without residues included weed free (R۰) and weedy check (R۱) as sub plot. The experimental design was a split plot based on randomized complete block in four replications. Results showed that the lowest weed biomass, highest grain yield and yield components of sunflower were obtained at ۱۵۰ and ۴۵۰ kg N ha-۱, respectively. Compared to weedy conditions, the lowest weed biomass (۲۸۴۷.۵۸ kg ha-۱) and the highest yield (۴۰۸۷.۶۷ kg ha-۱) of sunflower were obtained at ۷۵ and ۲۵ % residue, respectively. Optimum rates of nitrogen fertilizer and rapeseed residue to guarantee maximum grain yield and optimum suppression of weeds were ۴۵۰ kg ha-۱and ۲۵%, respectively. Generally, to increase sunflower yield and suppress weeds, it is recommended to integrate cultural practices with use of ۴۵۰ kg urea ha-۱ fertilizers and left over ۲۵% of rapeseed residue, was the best treatment.

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Keywords: Nitrogen , Residue , weed , Yield