Natural Plant By-Products and Mulching Materials to Suppress Weeds and Improve Sugar Beet (Beta vulgaris L.) Yield and Quality

To reduce the use of herbicides in agriculture, there is an urgent need to look for cost-effective and environmentally friendly non-chemical methods to control weeds in field crops. Plant by-products could be exploited directly as plant residues or indirectly as plant extracts for weed control. Thus, the objective of this study was to evaluate the effectiveness of several plant wastes and extracts in controlling weeds of sugar beet ( Beta vulgaris subsp. vulgaris ) with enhancing yield and quality. Three weed control groups of twelve practices were examined. The first weed control group included three aqueous extract concentrations (15, 20, and 25%) of Plectranthus amboinicus L. The second weed control group involved six soil mulching plant materials [rice ( Oryza sativa L.) straw, wheat ( Triticum aestivum L.) hay, peanut ( Arachis hypogaea L.) straw, mango ( Mangifera indica L.) leaves, flax ( Linum usitatissimum L.) meal, and soybean ( Glycine max (L.) Merr.) meal], while the third group comprised of desmedipham/ethofumesate/lenacil/phenmedipham (DELP) herbicide 1.5 L ha −1 [desmedipham 70.5 g active ingredient (ai) ha −1 + ethomesufate 112.5 g ai ha −1 + lenacil 40.5 g ai ha −1 + phenmedipham 90 g ai ha −1 ], hoeing, and unweeded check. During a 2-year field trial (2019/20 and 2020/21), the 12 weed control treatments arranged in a randomized complete block design (RCBD) and replicated three times. Compared to the recommended applications (hoeing and herbicide), reduction averages of both seasons for total weeds biomass were 46.3–54.2%, 37.3–46.4%, and 23.0–34.4% due to rice straw, wheat hay, and mango leaves, respectively. Root and sugar yields of sugar beet divulged the highest values with hoeing in both seasons statistically equaling ( P ≥ 0.05) rice straw and wheat hay for root yield and wheat hay for sugar yield in the first season. Except flax meal, all weeded treatments in the first season as well as mango leaves, wheat hay, peanut straw, and hoeing in the second one caused significant ( P ≤ 0.05) reductions in sodium content of beet juice. Wheat hay, mango leaves, and hoeing in both seasons, in addition to rice straw, peanut straw, and herbicide in the first season, were the most efficient practices for improving sucrose % and extractable sugar %. Compared to hoeing, reductions in net return were –286.7 and –320.0 ($ ha −1 ) by percentage of 6.5 and 7.2, due to mulching soil by rice straw and wheat hay, respectively. Recycling the plant by-