Weed management in sorghum [Sorghum bicolor (L.) Moench] using crop competition: A review

The food security of many developing countries relies on sorghum production due to its low input requirements and ability to endure extreme climatic stresses. This C4 grass species is widely cultivated for grain, feed/fodder, and bio-fuel uses in tropical and semi-arid areas of the world. A high efficiency water utilization mechanism and tolerance to drought and high temperatures favours it as an alternative crop to maize in areas with marginal water availability. Despite of its potential, this crop is underutilized given few weed management options. In addition to other biotic and abiotic factors, weeds are considered to be a major constraint, causing 15-97% losses for sorghum growth and yield under different climatic conditions. Previous studies where the crop spacing, seeding rate, and selection of competitive cultivars were altered, highlighted the importance of weed management through cultural practices or crop competition. Narrowing the crop rows and increasing plant densities were found effective in reducing the growth, biomass, and competitive ability of several weed species in sorghum. In addition, selection of competitive and allelopathic sorghum cultivars affected the weed seedling emergence by decreasing light interception and by releasing numerous allelochemicals. However, a review of the literature directed our attention towards some neglected points of weed management through crop competition in sorghum. For instance, crop row orientation has not been studied yet to investigate its influences on weed competitiveness against sorghum around the world. There is a dire need to diversify cultural practices in agro-ecosystems as much as possible to provide competitive advantage for the sorghum crop. Future research should be planned to evaluate the effectiveness of different sowing rates, dates, and directions on the crop yield and weed suppression under different cropping systems. Furthermore, cultural practices should be integrated with other weed management techniques for the development of a more reliable and sustainable weed control program in sorghum.