Understanding the Long-Term Weed Community Dynamics in Organic and Conventional Crop Rotations Using the Principal Response Curve Method

Abstract

Weeds have acquired evolutionary adaptations to the diverse crop and weed management strategies used in cropping systems. Therefore, changes in crop production practices such as conventional to organic systems, tillage-based to no-till systems, and diversity in crop rotations can result in differences in weed community composition that have management implications. A study was carried out to understand the weed community dynamics in a long-term alternative cropping systems study at Scott, SK, Canada. Long-term (18-yr) weed community composition data in wheat (Triticum aestivumL.) in ORG (organic), RED (reduced-input, no-till), and HIGH (high-input, conventional tillage) systems with three levels of crop rotation diversity, LOW (low diversity), DAG (diversified annual grains), and DAP (diversified annuals and perennials), were used to study the effect of different cropping systems and the effect of environment (random temporal effects) on residual weed community composition using the principal response curve (PRC) technique. The interaction between cropping systems and year-to-year random environmental changes was found to be the predominant factor causing fluctuations in weed community composition. Furthermore, the single most predominant factor influencing the weed composition was year-to-year random changes. Organic systems clearly differed from the two conventional systems in most years and had more diverse weed communities compared with the two conventional systems. The two conventional systems exhibited similar weed composition in most years. In this study, the use of the PRC method allowed capture of the real temporal dynamics reflected in the cropping systems by time interaction. This study further concludes that moving from a tillage-based, high-input conventional system to a no-till, reduced-input system did not cause significant changes in the weed community composition throughout the time period, but diversity in organic systems was high, probably due to increased occurrence of some difficult to control species.

Plant community responses to integrating livestock into a reduced‐till organic cropping system

“…In conventional, high input systems synthetic herbicides provide a strong influence on weed communities by selecting against susceptible species (Smith and Mortensen 2017), and studies have consistently found lower weed biomass, species richness, and diversity in conventional systems compared with organic systems (Menalled et al 2001, Pollnac et al 2008, 2009, Benaragama et al 2019). Consistent with these findings, our conventional no‐till cropping system had the lowest weed biomass, species richness, and diversity of the three cropping systems.…”

Integrated Soil and Crop Management in Organic Agriculture: A Logical Framework to Ensure Food Quality and Human Health?

“…In between leys, organic farming regulations prescribe that farmers alternate crops from different plant families, and with contrasting life-cycles, canope structures, rooting patterns and periods of growth, to minimize the accumulation of crop species-specific weeds, disease and pest populations [6,[25][26][27][28]. Organic rotations are therefore thought to be, overall, more diverse than conventional crop rotations [31], but there is concern that organic ley/arable rotations are not diverse enough to deliver the desired agronomic gains (e.g., reduced weed pressure; optimum nutrient-use efficiency) [35,36]. Therefore, the identification of agronomically useful and economically viable break crops for organic ley/arable rotations remains a major challenge [36].…”

Weed competition in organic and no-till conventional soils under nonlimiting nutrient conditions

“…Common lambsquarters (Chenopodium album L.) was chosen as the model weed to impose competition on the crop, as it was the most common weed observed in the ACS study (Benaragama et al 2019). Weed competition treatment differed in the two years.…”