Weed population and interference response to sowing date and lentil (Lens culinaris Med.) cultivar in dryland condition of Khorramabad

Evaluation of weed population and their interference on lentil varieties at different sowing date was investigated in a field experiment in Khorramabad during 2005-06 growing season. The experimental design was a randomized complete block in factorial arrangement with 4 replications. The experiment had 3 factors including: planting date at three levels (autumn, winter, and spring) weed interference at two levels (weed free, and weed infested throughout the total growing season), and three lentil varieties (Gachsaran, Flip93-93, and Lorestan landrace). Broad leaf weed species relative frequency for autumn lentil was more than winter and spring lentil 77.8 and 345.7% respectively. The highest level of relative frequency, and importance value in all sowing dates was belonged to safflower (Carthamus oxyacantha) and bedstraw (Galium tricornutum). Weed population severely decreased as sowing date delayed, so that average weed density for winter and spring lentil was only 40.5 and 4.3% of weed density in autumn lentil. There were not significant differences between autumn and winter lentil from the viewpoint of weed biomass. Spring lentil weed biomass was lower than 1/5 averaged over winter and autumn lentil. In autumn and winter lentil weed interference caused yield loss by 32.6 and 33.5% respectively. Yield loss due to weed interference for spring crop (22.3%) was significantly lower than for two other sowing dates. Lentil variety effect and its interaction with sowing date on weed population characteristrices were not significant.