Does yield loss due to weed competition differ between organic and conventional cropping systems?

Abstract

High weed abundance in organic crops is thought to be a key factor contributing to the greater yield loss in organic as compared with conventional cropping systems. However, even with greater weed densities than conventional systems, some organic systems have yields comparable to conventional systems, suggesting that cropping systems might differ in yield loss due to weed competition. The diversity in soil nutrient resources due to diversity in crop rotations and variable inputs might enhance crop tolerance to weed competition. We assessed the long-term effects of contrasting levels of crop rotations (low, medium and high diversity) on weed density, weed biomass and wheat yield loss in organic and no-till conventional cropping systems using a microplot study within a long-term cropping systems trial at Scott, Saskatchewan, Canada. Weed density and biomass were found to be four times higher in the organic systems than in the conventional systems. Under standard weed management practices, organic had 44% lower yield than the conventional system. Lower yields in organic, even without weed competition, suggest that the lower yields are due to low soil productivity rather than weed competition. No differences in yield loss were observed among the organic and conventional systems or among the diverse crop rotations. We conclude that the organic management practices and/or increased crop rotation diversity did not enhance yield or reduce yield loss due to weed competition, due to the factors associated with lower soil fertility.

Undersown cover crops have limited weed suppression potential when reducing tillage intensity in organically grown cereals

“…The weak crop stand in RT was naturally a poor competitor against weeds, resulting in high weed biomass production. The confounding factors affecting weed occurrence, and consequently crop yield, were demonstrated in earlier studies (e.g., Benaragama et al 2016;Woźniak and Soroka 2018).…”

Density of Competition between Species of Urochloa Sp. in Soybean Cultivation

“…These authors reported the plasticity of the more tolerant species as submitted to competitions with other plants. Benaragama et al (2016) found an invasive plant population of 40% higher in relation to the conventional organic crop system with a lower production of approximately 50%, showing the necessity of controlling invasive plants in crops.…”

Weed-plant interactions

“…However, these empirical studies without a theoretical base often conclude with the requirement for more knowledge about what drives the crop-weed interaction in order to recommend general outcomes. A mounting number of studies have been conducted to evaluate how cover crops can influence weed population dynamics by maximizing competition with weeds (Mirsky et al 2013;Den Hollander et al 2007) and, when intercropped, minimize competition with the cash crop while maximizing competition with the weed (Benaragama et al 2016;Hartwig and Amon 2002). In addition, some cover crops with legume species change the soil nitrogen dynamics favouring the crop or some of the weed species with little knowledge to base generalized weed management recommendations.…”