Rice (Oryza sativa L.), maize (Zea mays L.), and wheat (Triticum aestivum L.) provide approximately two-thirds of all energy in human diets, and the four major cropping systems in which these cereals are grown represent the foundation of the human food supply (Cassman, 1999). These cereals are essential for food security, especially in the developing world. Wheat is the most important staple crop in temperate zones, ranking first in total harvested area and third in total harvested area after maize and rice, and is known for adapting to a wide range of climate, elevation, and soil characteristics (Kizilgeci et al, 2021; Shewry & Hey, 2015; Zhao et al, 2019). Wheat plays a vital role in ensuring food and nutritional security as the most important cereal; 36% of the world's population consumes food, from which 20% of the calories and 55% of the carbohydrates are derived (El Sabagh et al, 2021). Ethiopia is one of the largest wheat producers in sub-Saharan Africa, ranking second after South Africa in terms of total wheat area coverage and the amount produced (Hei et al., 2017). Wheat ranks fourth after teff, maize and sorghum in area coverage and third after maize and teff in total production (Anteneh & Asrat, 2020). However, the average national wheat yield is low due to biotic and abiotic factors despite showing an increasing trend from 0.23 to 2.97 t/ha between 2013 and 2018 (CSA, 2018).
Crop production systems are facing challenges due to climate change and an increasing population (Abi Saab et al., 2019), and crop management requires significant investment to achieve environmentally friendly and ecologically sustainable yield and quality production. Wheat research has focused mainly on attaining high yields and neglecting yield stability; however, yield stability has become increasingly important in the face of climate change driven by agronomic factors, including crop rotation, integrated crop protection, soil tillage, fertilization and seeding density, in addition to environmental and genetic factors (Macholdt and Honermeier, 2017). Weeds are among the major yield reducing factors in cereal-dominated cropping systems because they compete for water, light and nutrient resources, thereby reducing yield potential. Cereal monocropping coupled with repeated applications of broadleaf herbicides has increased the density of problematic grass weeds (Birhanu, 1985; Tanner and Giref, 1991), whose widespread infestations are aggravated by increased usage of N fertilizers as well as noncompetitive semidwarf wheat varieties (Balyan et al., 1991; Tanner et al., 1993). With the wide use of combine harvesters, the ability of wild oat plants (Avena fatua) to remain in the soil without loss of viability for many years and their morphological similarity with cereal crops during the early growth stage are factors that increase the difficulty of developing control strategies. Weeds can be effectively controlled by increasing plant density, proper tillage, delayed planting, crop rotations, hand weeding, chemical control, and a combination of these factors. Several reports have indicated that higher crop density reduces yield loss due to severe infestation of cereals by wild oat species (Radford et al., 1980; Carlson and Hill, 1985; Martine et al., 1987; Torner et al, 1991; Scursoni et al., 1999). Raising the seed rate from 120 to 150 kg/ha was 27% more effective at reducing wild oat in Egypt (Hassanien, 1998), and increasing the seed rate from 63 to 135 kg/ha reduced the wild oat density by 35% in Canada (Friesen, 1973). A preliminary observation conducted at the Sinana station during 1998–2000 indicated greater grain yield and effective weed suppression as a result of a greater seed rate of 200 kg/ha. However, in other studies, increasing the seed rate had no impact on weed density, but the fresh biomass of weeds and the labour required for weed removal decreased with increasing seed rate (Amanuel Gorfu and Assefa Taa, 1992). It is common for farmers in Ethiopia to lose up to 40% of their crops because of weed infestations (Desta, 2000; Rezene, 2005). A wide range of 48–86% yield loss was also reported at a maximum weed density of 320 weed plants/m2 across species (Taye et al, 1996; Rezene and Yohannes 2000). Hand weeding is a labour- and time-consuming task that takes up to 140 hr/ha because crops are normally not row-planted, making mechanical control difficult. Integrated weed management, which involves increasing the seeding rate, reducing the dose of herbicide and early application during the crop and weed growth stages followed by hand-weeding at later stages, has led to significant improvements in crop yield and sustainable weed management in major wheat-growing areas of southeastern Ethiopia (Deressa & Fana, 2010).
Depending on the management, environment, and genotype, the seeding rate impacts wheat tillering, grain yield and protein; hence, achieving higher agronomic performance and better end-use quality requires optimizing and periodically reviewing management practices such as seeding rates (Haile et al., 2013). Wheat quality was not reduced at higher seeding rates, as protein content, kernel weight and test weight were unaffected; however, in other instances, the protein concentration decreased as seeding rates and yield increased (Haile et al., 2013). Conservation tillage and crop rotation are among the factors that enhance the productivity of cropping systems via N fixation by legumes, life cycle interruption of yield-reducing biotic factors, improvement of soil tilth, crop diversification and reduced soil erosion (Bogale & Fana, 2018). The southeastern highlands of Ethiopia are dominated by cereal monocropping, where wheat and barley are dominantly grown annually. This monocropping trend aggravated the prevalence of grassy weed species that resemble cereals in terms of their growth requirements, increasing the difficulty of weed control. Therefore, the objective of the present study was to evaluate major weed management options for wheat production and weed control.