Investigating the Effect of Weeding and Plant Density on some Characteristics and Yield Loss of Red Bean (Phaseolus vulgaris L.)

Introduction Beans (Phaseolus vulgaris L.) are one of the most important sources of protein and minerals for humans, and their residues and straw are also rich in nutrients necessary for animal nutrition. This plant species plays an important role in sustainable agriculture due to its morphological characteristics and nitrogen fixation. Crop husbandry practices are very important in maximizing plant’s access to environmental factors and hence its yield potential. Among the most important crop management practices is weed management. Weed control practices such as using optimal planting density and weeding at the right time are more appropriate particularly in terms of minimizing pesticide applications and hence achieving sustainable agriculture. In addition to reducing the quantity and quality of grain yield of beans, weeds cause problems in planting, maintaining, and harvesting operations of this plant. It has been reported that the lack of weed management and control may cause grain yield reductions of up to 83% in beans, as weeds outcompete the weed crop in accessing water, nutrients, and light. Materials and Methods This research was conducted in Agriculture Center of Al-Mahdi town, Azna, Lorestan Province, west of Iran as a factorial experiment in randomized complete blocks design ith three replications in 2011. Experimental treatments included weeding factor at six levels of: 0 (no weeding), 14, 28, 42 and 56 days after crop emergence (DAE), and complete weeding during the growth period and the planting density at two levels: 40 and 50 plants/m2 of red beans (Sayyad cultivar(. The land had been left fallowed the year before planting. After moldboard-plowing and disc-harrowing the land, seeds were planted into a depth of 5 cm in plots of 3 × 3 m. Irrigation was carried out during the growing period of beans by flooding method, every 5 to 7 days according to the environmental conditions. Fertilizers were used as 100 kg ha-1 triple superphosphate and 50 kg/ha urea before planting and also at 50 kg ha-1 urea as top-dressing at the beginning of flowering. The evaluated traits included plant height (cm), days to physiological maturity, pods/plant, grains/m2, grains/pod, branches/plant, 100-grain weight (g), plant above-ground dry weight (g/m2), grain yield (g/m2), harvest index (%), yield loss due to weed competition (%). SAS statistical software was used to analyze the data and LSD test was used to compare means of main effects and interactions. Results and Discussion The effect of experimental factors on all measured traits in red beans (Sayyad cultivar( was significant. Among the weeding treatments, besides complete weeding, the most desirable values of measured traits including plant height, days to physiological maturity, pods/plant, 100-grain weight, plant above-ground dry mass, grain yield and yield loss due to weed competition were obtained in weeding at 28 DAE. However, the highest grains/pod and harvest index were obtained in weeding at 42 and 56 DAE, respectively. Increasing planting density increased the plant height, plant above-ground dry mass, grains/m2, and grain yield, despite decreasing the remaining traits. The interaction effect of planting density and weeding time were significant on branches/plant, grains/m2 and grain yield. The highest branches/plant (4.8) was obtained in weeding at 28 DAE and planting at 40 plants/m2, the highest grains/m2 (1815) and grain yield (3869 kg/ha) were observed when weeding was done in 28 DAE and planting was done in 40 plants/m2. The correlation coefficients of grain yield with grains/m2, 100-grains weight, pods/plant and grains/pod were 0.88**, 0.85**, 0.79** and 0.40*, respectively, indicating a greater role of grains/m2 in regulating grain yield than other yield components. Therefore, crop management practices toward appropriate time of weeding and planting density will guarantee a maximum grain yield of bean, at leat when Sayyad cultivar is cultivated in Azna region. Conclusions Our results suggested that weeding time and planting density are crucial in obtaining acceptable grain yield in red bean (Sayyad cultivar). With weeding at 28 DAE and planting at 50 plants/m2, it is possible to obtain 82% of grain yield obtainable in complete weeding and achieve the appropriate productivity of red bean cultivation in Azna.