determination of effect of concentration and application time of paraquat desiccant on grain yield and yield components of faba bean (vicia fabae l.) in different planting dates

faba bean is one of the proper crops for cultivation in guilan climate conditions in rotation with rice. one of the limiting factors in development of cultivating this plant is late maturity and synchronizing of its ripening with rice transplanting. to investigate the effect of planting date, timing and consumption rate of paraquat herbicide on the ripening, grain yield and some of the agronomic traits of vicia faba l. (var. barekat), a split factorial experiment was conducted in a complete randomized block design with 21 treatments and three replications at rice research institute of iran (rasht) in 2009-2010 cropping season. experimental treatments were three planting dates of 2 and 17 october and 1 november as main factors, consumption rate of paraquat in three levels of 0.2, 0.4 and 0.6 kg.ha-1 of active ingredient and two application times of grain moisture content of 40% and 60% for pods in one third of plant bottom as sub plots as well as three control treatments of the planting dates of 2 and 17 october and 1 november. the results showed that there is not statistical difference between the use of desiccant and control in grain yield and yield components. although, the use of desiccant had negative effects on protein percent and protein yield. among the studied treatments, maximum grain and protein yields were obtained in planting date of 17 october, consumption rate of 0.2 and 0.4 kg.ha-1 of active ingredient in application time of 40% of grain moisture with average of 830.7 and 824.8 g/m2, respectively. planting date of 2 october, consumption rate of 0.6 kg.ha-1 of active ingredient in application time of 60% of grain moisture had the lowest grain and protein yields. maximum and minimum growth duration were obtained for control treatment in planting date of 2 october with average of 239 days and planting date of 1 november, spraying in the step of 60% of grain moisture and concentration of 0.6 kg.ha-1 of paraquat active ingredient with average of 221 days, respectively. based on the obtained results, it seems that consumption of the desiccant had no negative effect on grain yield and can be used for early harvesting faba bean. planting date of 17 october, consumption rate of 0.4 kg.ha-1 of active ingredient in application time of 40% of grain moisture reduced the growth duration (4 days) and is recommended as better treatment.