Effects of plant density on seed yield and oil percentage of rainfed safflower under weedy and weed-free conditions

Increasing crop competitiveness against weeds through crop management has been proposed as an agro-ecological approach. In this research, the effect of plant density on weed control, and determining proper seeding rate and row spacing was investigated. This experiment was conducted in a factorial strip-block in a randomized complete block design (RCBD) with four replications. The experiment was repeated in three cropping seasons (2007- 2010) under rainfed condition. Weed conditions with two levels (weedy and weed free) was considered as horizontal factor and plant density (40, 70, 100 and 130 plant m^-2) and row spacing (15, 30, 45 and 60 cm) were combined as factorial treatments and considered as vertical factor. Results of combined ANOVA showed that the seed yield was significantly influenced by year, which showing diverse environmental conditions in the experiment. The weed and row spacing treatments had significant effects on grain yield, where weed-free treatment with 334 kg/ha, 15 cm row spacing with 349, and 30 cm row spacing with 329 kg ha^-1 had the best yield production among the treatments. The results indicated that oil seed percentage in weed-free condition with mean value of 30.9% was significantly higher than weedy condition with mean value of 29.2%. Interaction between weed condition and row spacing was significant and the highest oil percentage was achieved in 30 and 45 cm row spacing under weed-free condition. Mean comparison for oil percentage based on plant density showed that the treatments of 40 and 70 plant m^-2 had significantly higher oil percentage than the treatments of 100 and 130 plant m^-2. It can be concluded that less row spacing (15 cm) and medium seed rate (70 plant m^-2) can be recommended for higher seed yield and oil production in safflower.