Relationship Between Plant Density and Grain Yield of Three Pinto Bean Cultivars at Different Sowing Dates

In order to investigate the relationship between plant density and grain yield of three pinto bean cultivars at three different sowing dates, a split plot factorial experiment based on randomized complete block design (RCBD) and three replications was conducted in Zanjan Agricultural Research Center in 2003. Three pinto bean cultivars (Talash, Khomein 5 and COS16) at three different sowing dates (9 May, 21 May and 2 June) with four densities (15, 20, 25 and 3 plants/m2) were sown in a loamy soil. Days to flowering, pods per plant, seeds per plant, 100 seeds weight, days to maturity and grain yield were significantly affected by sowing date, cultivar and plant density. The interaction effects of sowing date and cultivar were olso significant for days to flowering, days to maturity and grain yield but interaction effects of sowing date and plant density were only significant for days to flowering and grain yield. All these traits were decreased with delaying in sowing date. Grain yield of COS16 was higher than that of Talash and Khomein 5. Days to flowering, pods per plant, seeds per plant, 100 seeds weight and days to maturity decreased, but empty pods per plant and grain yield per unit area increased, with increasing plant density. The relationship between plant density and grain yield of the three pinto bean cultivars were analysed, using equations 1/w = a+bp and y = p/a+bp, where: 1/w = reciprocal of yield per plant, y = grain yield per unit area, p = plant density, a and b = constants. The results indicated that delayed sowings reduce grain yield of low densities more than that of high densities. Consequently, estimated optimum economic densities for delayed sowings were more than those for early sowings. Therefore, it is necessary to increase seeding rate at delayed sowings, in order to prevent or to reduce the yield loss.