the critical period of weed competition in lentil (lens culinaris medik.) under kermanshah condition

introduction lentil (lens culinaris medik.) is an important legume in the mediterranean area. high protein content in lentil seed (about 22-28%) makes it as a good food source for developing countries and low-income people. in the west of iran such as kermanhah province, it is the most important pulse in rainfed systems cultivated traditionally in rotation with wheat and barley. lentil is grown either as a spring or a winter crop. the cold tolerant cultivars of lentil can be sown in the fall and have by to over 50% more than spring-sown cultivars. weed interference and moisture restriction are known as the most important factors affecting lentil yield. the average yield loss caused by weeds has reported about 84% in lentil. since lentil is categorized as a slow-rate growth crop especially during early stages, it is affected by weeds depressingly. the critical period for weed control is defined as a period in which weeds must be controlled to prevent un-acceptable yield loss of crop. knowledge of the critical period is useful in making decisions on the need for and timing of weed control and in achieving efficiently herbicide use from both biological and economical perspectives. in practical view, the critical period is defined as a number of weeks after emerging crop during which a crop must be free from weeds in order to prevent yield loss greater than 5%. this study aimed to determine the critical period of weed competition in lentil under the growing conditions of the kermanshah province. materials and methods this experiment was done at campus of agriculture and natural resource, razi university, kermanshah, iran, during 2009-2010 growing season. the experiment was conducted as factorial arrangement based on randomized complete block design with three replications. experimental factors were two lentil cultivars (gachsaran and local) and treatments of critical period of weed control. for the second factor, there were two sets of treatments. in the plots of first treatments, weeds were allowed to grow for 15, 30, 45, and 60 days after crop emergence, after which the plots kept fully free of weeds by harvest time. in the plots of second treatments, weeds were kept fully free of weeds for 15, 30, 45, and 60 days after crop emergence and then weeds were allowed to grow until harvest time. for both of them, there were full season-long weed-infested and weed-free plots as control treatments. weeds were cut from the soil surface and sorted by species, counted, and finally dried to measure above-ground dry matter. after physiological ripening of lentil, the crop was harvested and biomass, grain yield, 1000 grain weight, the number of pods per plant, the number of grains per plant and plant height were measured. results and discussion analysis of variance showed that grain yield, biological yield, pod weight in plant, grain weight in plant and plant height effected significantly by the weed interference period, while it not influenced significantly on 1000 seed weight. increasing in weed-free period caused reduction in weed dry matter and weed density whereas by prolonging the interference period, weed dry matter increased and weed density showed an upward trend until 45 days after emergence and had a sharp fall after that. the maximum weed interference period (beginning of critical period) based upon 5 and 10% level of grain yield loss for gachsaran cultivar were 17 and 21 days after emergence, while for local was 15 and 20 days after emergence, respectively. the minimum period of weed control (the end of critical period) based upon 5 and 10% level of grain yield loss were 63 and 56 days after emergence for gachsaran cultivar, and 62 and 54 days after emergence for local, respectively. conclusion according to this research, under kermanshah climatic conditions, the critical period of weed control based upon 5% level of grain yield loss for gachsaran and local lentil cultivars were obtained 46 and 47 days after emergence, respectively, and based upon 10% level of yield loss, critical period of weed control were 35 and 34 days after emergence, respectively. there was no significant difference between gachsaran and local lentil cultivars in terms of critical period of weed control.