Comparison of Critical Period of Weed Control in Two Planting Distances on Yield of Canola (Brassica napus L.)

To determine the critical period of weed control of two planting distances on canola yield, a factorial design with 3 replications was conducted using Hayola 401 variety, in paddy field of Rice Research Institute of Iran (RRII) in Rasht, during cropping season of 2006. Planting distances (15 and 30 cm) and hand weedings (12 treatments in two sets) were the two factors of the experiment. The hand weeding treatments were in two sets, the first set was weed free periods including cotyledon stage, 0, 2, 4, 8 leaf stages and flowering stage. The second set of hand weeding treatments was weed infested periods including cotyledon stage, 0, 2, 4, 8 leaf stages and flowering stage. The two sets of hand weeding treatments were fitted to Logistic and Gompertz functions to determine the critical period of weed control in this plant. Results showed that the effect of planting distances of canola, treatments of weeding, among weeded and unweeded treatments, and their interactions were significant on grain yield, biological yields, oil production and harvest index. There were significant differences between weed infested and weed free treatment in oil yield, grain and biological yields in each planting distances. The 30 cm planting distances had significantly higher grain yield (2502.4 kg/h) than 15 cm planting distances (2141 kg/h). The critical period of weed control for 15 cm distance was between 27 and 85 days after planting (DAP) (emergence to 10-leaf stage), and between 35 to 64 DAP (2-6 leaf stages), using 10 and 5% acceptable yield reduction, respectively. In 30 cm planting distances, these periods were between 32 and 95 DAP (2-10 leaf stages) and 50 to 77 DAP (4-8 leaf stages) using 10 and 5% acceptable yield reduction, respectively.