Evaluating Seedbed Preparing Methods and Herbicide Application in Weed Management of Common Bean (Phaseolus vulgaris L.)

Phaseolus vulgaris L., known as the common bean and green bean among other names, is a herbaceous annual plant grown worldwide for its edible dry seeds or unripe fruit. Weeds are one of the most important factors in reducing the yield of common bean. Since tillage promotes germination of many weed species, tillage followed by destruction of weed seedlings with minimal further soil disturbance often leads to lower weed density in the crop. This is referred to as the stale seedbed method of planting. In false seedbed technique, preparation of a seedbed is followed by one or more superficial cultivations as about one-week intervals prior to planting the crop. Although these procedures are widely used by farmer, they have received little scientific study. This experiment was conducted to investigate the combined method of using seed bean bed preparation with application of herbicides such as EPTC, linuron, and trifluralin, in order to bean weeds control in Aleshtar region.

In order to investigate the effect of seedbed preparing methods and soil applied herbicides in weed management and yield of common bean, an experiment was carried out as factorial in a randomized complete block design with four replications in 2015-2016 growing season in Hatam Abad village, Selseleh, Aleshtar, Lorestan, Iran. Experimental factors included seedbed at two levels (fasle seedbed and stale seedbed) and soil applied herbicides at three levels (EPTC (3 L ha-1), linuron (1.5 L ha-1), and trifluralin (1.5 L ha-1)). Two treatments including weed infested (as control) and weed free (as treatment), are also considered. Each plot was divided into two parts, one infested with weed (as contaminated control) and the other treated with herbicide. The percent reduction of weed density and dry weight were calculated at 30 and 60 days after spraying. The studied traits were plant height, number of pods per plant, number of branches per plant, length of pod per plant and number of seeds per pod, economic and biological yield and harvest index. The SAS9.2 software was used to analyze the data.

The results showed that weed dry weight reduction (79.09% and 78.57%) was greatest in stale seedbed plus EPTC and trifluralin at 30 days after herbicide application (DAHA), respectively. While, the lowest reduction in weed dry weight (28.27% and 35.41%) was observed in stale and false seedbed with linuron application. Weed dry weight reduction at 60 DAHA in false seedbed (76.58%) was lesser than stale seedbed (84.34%). The highest and lowest weed density and dry weight reduction percentages (90.38% and 89.69%) and (64.48% and 64.48%)) were obtained trifluralin and linuran, respectively. The highest percentage of increase in number of pods per plant belonged to weed free (52.01%), followed by linuron (42.5%), EPTC (40.43%) and trifluralin (34.34%). The highest percentage of increase in the number of seeds per pod belonged to weed free (36.14%) and then EPTC (29.54%), linuron (28.06%), and trifluralin (28.06%). Regarding grain yield, the highest percentages were weed free (52.92%), EPTC (44.11%), linuron (31.13%) and trifluralin (30.30%), respectively. The highest percentage of biological yield increase belonged to weed free (32.46%), linuron (25.5%), EPTC (20.81%), and trifluralin (17.83%), respectively. The highest percentage of harvest index belonged to weed free (34.33%), followed by linuron (21.37%), EPTC (19.55%), and Trifluralin (18.23%).

The result of present study showed that trifluralin could control weed more than EPTC and linuron. The weed dry weight reduction percentage in the stale seedbed was also higher than that of the false seedbed. In all treatment, the percentage of yield increase of weed free was higher than the other treatments. Except for grain yield, which showed a significant difference in herbicide treatments, other treatments did not differ significantly. Totally, the false seedbed technique has several limitations. First it can only be effective if the soil is warm and moist enough to allow germination of weed seeds. A second limitation is that the soil is kept bare and loose for a more period, and this may lead to more erosion. A third limitation is that yield may be lost if planting is delayed by the pre-plant cultivation. A fourth problem is that although cultivation prior to planting may greatly reduce one set of species, if planting is delayed, a new set of species may become physiologically ready to germinate.