Effect of Row and Plant Spacings on Weed Competition with Pinto Beans (Phaseolus vulgaris L.

Field experiment was conducted at the agricultural experiment station of Shiraz University at Kushkak in 1996 to quantify the competitive ability of pinto beans (Phaselus vulgaris L. var. Daneshjou) with a naturally occurring population of weeds. An attempt was made to increase the competitive ability of the plants by altering row and plant spacings. An uncontrolled population of weeds reduced pinto bean yields by 75%. The ability of plants to reduce weed dry weight was further enhanced in medium and narrow rows compared to wide rows. Row and plant spacing combinations which maximized leaf area index when grown under weedy conditions also had significantly less weed dry weight. however, row and plant spacings did not reduce weed density. A significant negative correlation was observed between weed dry weight with leaf area index and final yield of pinto bean. For each kg ha-1 increase in weed dry weight, the corresponding pinto bean yield loss averaged 260 g ha-1. Season-long weed competition significantly reduced total number of pods per plant, number of seed per plant, and 100-seed weight