Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Abstract

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2-year crop rotation were carried out in south-east Norway (60°42 0 N, 10°51 0 E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha À1 ). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, preemergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre-and post-emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre-emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4-year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.Keywords: annual weed, cover crop, weed control, non-herbicide weed management, manure fertiliser and cereals. STENERUD S, MANGERUD K, SJURSEN H, TORP T & BRANDSAETER LO (2015). Effects of weed harrowing and undersown clover on weed growth and spring cereal yield. Weed Research 55, 493-502.

Effect of annually repeated weed harrowing against Chenopodium album (L.) in organically grown spring cereals

“…Weed seed production is related to weed biomass (Wilson et al 1995), which implies that annually repeated weed harrowing could reduce the input to the weed seed bank in the long term. The suggestion is not supported by Norwegian studies (Stenerud et al 2015) in which the seed bank increased after post-emergence weed harrowing with a cover crop during the 4-year study period. Therefore, seed bank dynamics merit more comprehensive studies.…”

“…In Norway, Brandsaeter et al (2012) reported that the average control effect of pre-emergence weed harrowing on C. album was 36% and that of post-emergence harrowing was 62% in spring cereals. Furthermore, Stenerud et al (2015) succeeded in reducing the weed density by 59% and weed biomass by 67% when combining pre-and post-weed harrowing in spring cereals. However, the combination did not provide more long-standing weed suppression than pre-and post-emergence weed harrowing applied alone.…”

“…Typically, annual broad-leaved weed species are the main targets of weed harrowing (Wilson et al 1993, Rasmussen et al 2010 and the timing of harrowing should strike a balance between susceptibility of weed seedlings and avoidance of crop damage (Hansen et al 2007, Lundkvist 2009). Knowledge about weed control efficacy and yield response is available from field experiments with cereals in the Nordic countries, where pre-emergence ("blind harrowing"), post-emergence weed harrowing and their combinations have been studied (Lötjönen and Mikkola 2000, Rasmussen and Rasmussen 2000, Lundkvist 2009, Stenerud et al 2015. However, results have not been consistent, depending on target weed species, soil type, crop competition and time and subject of assessment.…”

“…Competitive ability of the crop plays a central role in weed management, both from an annual and a long-term perspective (Lundkvist et al 2008). It has been hypothesized that crop competition could be increased, and consequently weed biomass decreased, by sowing cover crops in cereal stands, but this has not been fully supported by the results from the field experiments under northern European conditions (Rasmussen et al 2006, Sjursen et al 2012, Stenerud et al 2015, Salonen and Ketoja 2020.…”

Intercropping with service crops provides multiple services in temperate arable systems: a review

“…Queen et al (2009 showed that the amount of light reaching red clover through a wheat canopy was greatly lower with the application of increasing amounts of nitrogen. Conversely, legume service crop biomass is generally greatest in the absence of nitrogen application (Pearson et al 2014;Stenerud et al 2015;Vrignon-Brenas et al 2016a). Furthermore, the localized application of fertilizer to maize rows did not favor ryegrass grown as a service crop (Garibay et al 1997).…”