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

Abstract

Adoption of reduced tillage in organic cropping has been slow, partly due to concerns about increasing weed infestation. Undersown cover crops (CCs) are considered to be a feasible option for weed management but their potential for weed suppression is insufficiently investigated in low-till organic cropping. The possibilities to reduce primary tillage by introducing CCs to maintain weed infestation at a level that does not substantially jeopardize crop yield were studied in a field experiment in southern Finland during 2015-2017. Eight different CC mixtures were undersown in cereals and the response in weed occurrence was consecutively assessed in spring barley, winter wheat, and finally, as a subsequent effect, in spring wheat. Growth of CCs was too slow to prevent the flush of early emerging weeds in spring barley whereas in winter wheat, CCs succeeded in hindering the growth of weeds. However, CCs could not prevent the increase of perennial weeds in a reduced tillage system in which the early growth of spring wheat was retarded in cool 2017. Consequently, after 2 years of reduced tillage, weed biomass was about 2.6 times higher and spring wheat yield was 30% lower than in plowed plots, respectively. No major differences in weed control efficacy among CC treatments were evident. A grain yield benefit was recorded after repeated use of leguminous CCs. The need for long-term field studies remains of particular interest regarding post-harvest performance and influence of CCs on perennial weeds before the inversion tillage.

A Review of Non-Chemical Management of Couch Grass (Elymus repens)

“…At the same time, incentives for farmers were introduced in many countries with the aim to reduce soil cultivation and to preserve soil structure and moisture and prevent erosion. Unfortunately, reduced tillage tends to favor perennial weed species, thus changing the composition of plant populations towards species which are difficult to control and have a high crop yield reduction potential (e.g., [72,73]). Glyphosate made it possible to control E. repens and some other perennial weeds as well as overwintering annual species such as Tripleurospermum inodorum, Stellaria media, and Poa annua when reducing tillage [74,75].…”

Evaluating Different Catch Crop Strategies for Closing the Nitrogen Cycle in Cropping Systems—Field Experiments and Modelling

“…However, within the last decade agricultural policies focused increasingly on the integration of CC in arable systems. This has been driven by the 'multifunctional benefits' of CC, including reduction of runoff and soil erosion, increases in soil C sequestration, weed suppression, a reduction in N leaching, and in the case of a legume CC a valuable N source [4,5], and especially Catch crops in the autumn/winter period are mandatory in Denmark, and subsidized in Norway, Sweden, and Finland [6]. Triggered by the 'greening direct payment strategy' in Germany [7], the arable land with CC is also rapidly expanding [8].…”

Thirty‐six years of no‐tillage regime altered weed population dynamics in soybean

“…Annual dicot weed species were more dominant in NT than in CT in both study years (2016 and 2017). Studies have reported that long‐term NT systems recorded greater total as well as broadleaf weed densities compared to CT (Kadziene et al., 2020; Salonen & Ketoja, 2020). The generally higher densities of winter species compared to summer species in the seedbank can be explained by the absence of weed control measures during the winter fallow season.…”