The Effect of Weeds Interference Time and Plant Density on Weeds Control and Broad Bean (Vicia faba L.) Yield

Broad bean (Vicia faba L.) belongs to the Fabaceae family and is the most important protein plant in the world. Although broad bean used as cover crop is able to deal with weeds, but the evidence show that yield of the plant decreased 32-82% because of competition with weeds. Using crop density is one of the ecological approaches in weed management. Broad bean density can produce biomass, weed competition, seed yield and ultimately influence the economic yield. Many reports show that increasing crop density reduced negative effects of weeds. The aim of this experiment was to evaluate the effect of weeds interference and different densities of broad bean on density and biomass of weeds and broad bean seed yield.
The experiment was carried out as split plot in randomized complete block, with four replications, during 2009-2010 in a field experiment at Ramin Agricultural and Natural Resources University, Ahwaz. Weeds interference was investigated on 5 levels, including V5, V9, V13 broad-bean phonological stages, full season weeding and full season weeds interference selected as main plots, and broad-bean density on 3 levels: including 8, 11 and 14 plants m-2 as subplots. Density, dry weight and diversity of weeds and seed yield of broad bean were evaluated.
The results showed that the weeds including wild beet, field bindweed and mallow had the highest occurrence (26.35, 21.17 and 18.46 plants m-2 respectively) in V9 broad-bean phonological stage, where the peak abundance of weeds was observed. The frequency of mallow, clover and yellow alfalfa were high until V5 broad-bean phonological stage, but in the next stages, they were replaced by other weeds and sorrel. It was also observed that the environmental factors can affect composition of weeds, for example, as the temperature increased in the early spring, an increase in the density of field bindweed was recorded. In the treatment of 8 plants m-2 of broad-beans, the highest frequency was recorded for mallow, clover and wild beet (15.2, 14.18 and 13.68 plants m-2). With the increased interference time period, from V9 broad-bean phenological stage on, the weed density was reduced due to "within species"(intra_species) competition of weeds and "between species" (inter_species) competition of weeds and the crop. As the time period of weeds interference increased, the dry weight reached its highest level, so that in full season weeding treatment, it reached 172.99 g m-2. Increasing the density of broad-bean from 8 to -14 plants m-2, decreased the weeds total dry weight from 92.42 to 83.76 g m-2 .Also increasing the weeds interference duration, reduced the seed yield, so that the highest yield, with the average of 2473.5 kg ha-1, was obtained in full season weeding treatments. Among the treatments of broad-bean density, the highest seed yield of 1342 kg ha-1 in average, was obtained from density treatment of 14 plants m-2. Among the treatments of interaction, weeds interference and Broad-bean density, Broad-bean density had a significant effect on the seed yield. The highest seed yield was observed in full season weeding treatment and the density of 14 plants m-2, with an average of 2699.87 kg ha-1, and the lowest seed yield was recorede in the treatment of full season interference and density of 14 plants m-2 with an average of 228.309 kg ha-1.
Considering the results of this study, where weeding is not to be applied in V13 broad -bean phenological stage and next stages, the minimum density (8 plants m-2) is recommended, because density had no significant effect on broad-bean yield, this would reduce the cost of production.
It can be concluded that increasing the duration of weeds interference, reduced the seed yield and weeds density while it increased the weeds dry weight. Increased broad-bean density, also, reduced the density and dry weight of all the weeds. The best time to control weeds for optimum performance of broad-bean, was prior toV13 broad-bean phenological stage.