Introduction: One of the key factors contributing to crop yield reduction is competition with weeds, which can greatly reduce the density and growth of crops. Among the most important legumes in the world, beans have become a popular substitute for animal protein and are one of the highest-producing legumes in Iran, following chickpeas. Weeds present a major challenge to maximizing bean production as they compete with beans for essential resources such as light, water, and nutrients. Additionally, weeds can impede harvesting operations and negatively impact the overall quality of the final product. In unmanaged environments, the presence of annual weeds caused a 70% reduction in the yield of white beans. Specifically, for each kilogram of dry matter comprised of annual weeds, the yield of white beans decreased by 0.38 kg per hectare. The choice of cultivar and planting date can have a significant effect on the weed population and growth in white bean fields. Different cultivars have varying levels of competitiveness with weeds, which can impact the overall weed population in the field. Similarly, the timing of planting can also affect weed growth and development. Research has shown that certain white bean cultivars, such as 'ICA Pijao' and 'Goyas', have greater competitiveness with weeds than other cultivars like 'Tacarigua'. This means that fields planted with these more competitive cultivars may experience lower weed populations compared to those planted with less competitive cultivars. Planting dates can also play a role in weed management. Early planting can allow for rapid crop establishment, which can help suppress weed growth by competing for light, nutrients, and water. However, early planting may also coincide with peak weed emergence, which can lead to increased competition between the crop and weeds. Conversely, late planting may result in slower crop establishment and reduced competitiveness with weeds, leading to higher weed populations. However, late planting may also allow for the use of pre-plant or pre-emergent herbicides, which can help to control weed populations prior to crop emergence.
Materials and Methods: An experiment was conducted at Boroujerd Research Station in 2015–2016 as a split factorial in a randomized complete block design with 4 replications to evaluate the effects of planting dates and white bean cultivars on the weed population. Planting dates (21 April, 10 May, 31 May, and 20 June), bean cultivars (Line GOYONOK98 and the Almas), and weed-free and weed-infested treatments were all investigated. Data variance analysis was done using SAS 9.4 statistical software, and graphs were drawn by Excel software. The mean comparison of the desired traits was also done by Duncan's test at the 5% probability level.
Results and Discussion: The findings revealed that delaying the planting date increased the percentage of frequency, density, and weed dominance. Pigweed (Amaranthus retroflexus L.) was the most important weed species in the experiment, with the highest frequency (85.41 percent), dominance rate (39.2 percent), and biomass (711.09 g/m²). The second planting date had the highest weed frequency (54.5 percent), which increased by 34.85, 29.61, and 19.16 percent, respectively, compared to the first, third, and fourth planting dates. Weed densities were lowest on April 20 and highest on May 30, with an average of 85.76 and 195.66 plants per m^-2, respectively. A 20-day delay in planting resulted in a 46.45 percent increase in weed biomass. In addition, the first and second plantings had the lowest and highest weed biomasses, with averages of 1139.65 and 2128.35 g. m^-2, respectively. According to the results of this experiment, planting an indeterminate -growth cultivar of Almas on April 21 was the best candidate for cultivation in Boroujerd due to reduced weed biomass.
Conclusion: The experiment's findings indicate that achieving the maximum yield of white beans is only possible when one has a good understanding of various factors such as climatic conditions, agricultural practices, and environmental stresses. Planting white beans at the beginning of May was observed to result in the lowest population and biomass of weeds due to unfavorable growth conditions for weeds like low temperature and light intensity. As a result, beans had ample growth opportunities without weed competition, resulting in considerable reductions in weeding and weed control costs and ultimately leading to the highest seed yield. In conclusion, early May planting is more advantageous than other dates regarding water resource accessibility and weed competition.