Crop–Weed Competition

Abstract

Competition from weeds is the most important of all biological factors that reduce agricultural crop yield. This occurs primarily because weeds use resources that would otherwise be available to the crop. The magnitude of yield loss is affected by numerous agronomic and environmental factors, most importantly, weed density and time of emergence relative to the crop. Practices that (1) reduce the density of weeds, (2) maximise occupation of space or uptake of resources by the crop or (3) establish an early‐season size advantage of the crop over the weeds will minimise the competitive effects of weeds on crops. Longer term management of crop–weed competition can be achieved through crop rotations, specifically crop sequences that reduce the weed seed bank, and therefore seedling density, and prevent proliferation of perennial weeds. Key Concepts Plant growth requires sunlight, water and nutrients, which in turn are converted into biomass that captures additional resources. In crop or weed monocultures, increasing density increases total production to a maximum that is determined by the resource status of the site, generally with a corresponding decrease in per plant mass. In crop–weed mixtures, increasing weed density results in large initial reductions in crop yield, again reaching an asymptote of maximum yield loss that varies among crop species, environments and weed cohorts. Farmers manage crop–weed competition by (1) reducing weed density (i.e. ‘weeding’), (2) establishing an early‐season competitive advantage to the crop and (3) maximising resource capture by the crop using competitive species, competitive cultivars, high sowing densities, optimal spatial arrangement, intercropping complimentary species or transplanting.

Effects of Intra- and Interspecific Plant Density on Rhizosphere Bacterial Communities

“…Plant-plant interactions can be both positive (facilitation) and negative (competition). In most plant communities, the latter dominate, reducing individual plant growth, including root growth, and although positive effects can also be important in some situations (Gallandt and Weiner, 2015), competition among plants is one of the major determinants of plant community structure and dynamics (Hortal et al, 2017). Neighboring plants can belong to the same or different species, referred to as intraand interspecific interactions, respectively.…”

Effect of the relative time of emergence on the growth allometry ofGalium aparinein competition withTriticum aestivum

“…In cereals, their height and enhanced ability to compete for light are traits that confer great competitive ability (see Gallandt & Weiner ). Experiments with spring barley ( Hordeum vulgare L.) cultivars of contrasting competitiveness indicated that the genotypes with a strong competitive ability against weeds emerged earlier and had early stem extension, longer main shoots in the tillering stage and small leaf angles (Didon ).…”

Annual ryegrass (Lolium rigidum Gaud) competition altered wheat grain quality: A study under elevated atmospheric CO2 levels and drought conditions

“…In designing this investigation, it was recognised that weed competition with crop species is generally evaluated by growth and yield characteristics of the target plant, such as plant height, leaf area, tillering, vegetative biomass production and crop yield (Ziska & Dukes, 2011). It has also been shown that weeds negatively affect crops in many ways other than economic yield levels (Gallandt & Weiner, 2015).Work presented here specifically focuses on whether weed competition has an impact on wheat grain quality, a question which has been paid only minor attention in most previous studies. In this respect, there are three components of community assembly that are potentially relevant to crop-weed interactions: species richness/abundance, functional traits diversity and polygenetic diversity (Gibson, Young & Wood, 2017).…”