Relationship between speed, soil movement into the cereal row and intra‐row weed control efficacy by weed harrowing

Abstract

Summary Field trials were carried out at a single Danish and two Spanish locations. In Denmark, winter wheat was sown at 24‐cm row spacing allowing hoeing in the inter‐row area. Hoeing speeds of 2, 5 and 8 km h−1 were tested at the end of tillering, at the beginning of stem elongation or on both occasions. The crop was harrowed immediately after hoeing at the same speed. At the Spanish locations the winter barley was sown at a 12‐cm row spacing and harrowed only, at either pre‐emergence plus post‐emergence, or once post‐emergence at mid‐tillering at 2, 4, 6 and 8 km h−1. The depth of the soil layer thrown into the cereal row was measured at all locations. This layer ranged between 0.4 and 1.4 cm, depending on the site and on the treatment, but was generally higher following a single harrow treatment at all sites. The soil layer only tended to increase with faster speeds at the Danish location. On a more sandy soil and soil rolled prior to treatment, less soil was thrown into the cereal row. When two hoe + harrowing treatments were made, a finer soil structure was achieved. However, this did not affect the weed control. At the Danish location, initial intra‐row weeding efficacy of Brassica napus, based on plant number before and 7 days after treatment, was found to be low (21–41%) but increased to 74–79% when assessed after 45 days. Partial burial and bending of B. napus, together with crop competition, probably suppressed weed growth and enhanced final mortality. Uprooting was probably a more important cause of mortality for Stellaria media. At the Spanish locations, weeding efficacy of Papaver rhoeas was similar, ranging between 58% and 83% and this was achieved soon after harrowing. A thicker soil layer did not result in a greater weed kill. It was therefore suggested that burial alone could not be the main factor responsible for weed control in any of the cases studied. No reduction in wheat biomass, measured at the end of May, was found with increasing speed, or with repeated passes of the harrow. The results suggested that faster harrowing, which is economically more attractive for farmers, could be recommended. The soil layer thrown into the row was not found to be a useful parameter to predict the weed control efficacy in the cases presented.

Weed harrowing in winter cereal under semi-arid conditions

“…Rasmussen (1990), however, did not find a clear relationship between both. Also Cirujeda et al (2003) did not find efficacy increases when comparing 2, 5 and 8 km h -1 and Rydberg (1993) described the biggest weed reduction at 5 km h -1 and increasing harrowing speed up to 9 or 13 km h -1 did not improve weed control but could affect grain yield.…”

“…It tills the soil surface superficially, so that weed seedlings are uprooted and covered by soil. Some authors have suggested that the most important effect is covering (Jones et al, 1995), while in other experiments uprooting was probably the main cause (Kurstjens and Kropff, 2001;Cirujeda et al, 2003). Uprooting and covering may not completely kill the weeds, but the damage caused may be enough to slow down their growth (Lambain et al, 1993) although Rasmussen (1992) did not find that surviving weeds had a lower competitive ability.…”

“…Efficacy in pre-emergence is only expected if the majority of weeds germinate earlier than the crop (Rasmussen, 1996). Most of the trials described in the literature have been conducted in early postemergence of both the weeds and the crop and it is often recommended to harrow in early stages of the weeds, especially when tap-rooted weeds dominate (Wilson et al, 1993;Welsh et al, 1997;Cirujeda et al, 2003). Selective harrowing is not usually conducted as weeds are better controlled at early stages.…”

Weed Biology and Weed Management in Organic Farming

“…Under favourable conditions, weed harrowing may provide similar efficacy as herbicides but usually the control effects from harrowing are lower than those which can be achieved with chemical control. Efficacy of harrowing depends on many factors including crop species and weeds present, the development stages of crop and weeds, weather, soil type and harrow type (Cirujeda et al, 2003;Hansen et al, 2007;Jensen et al, 2004;Rydberg, 1994). Weed harrowing may be divided into two categories; pre-emergence harrowing, and post-emergence harrowing.…”

Mechanical weed control in organic winter wheat

“…In particular, the recent automated harrowing systems designed to vary in real-time the harrowing intensity, on the basis of crop and weeds detection by sensors, have showed to increase the harrowing efficacy and balance the trade-off between crop damage and weed control (Rueda-Ayala et al, 2013). Indeed, harrowing intensity refers to the cultivation aggressiveness of the tines penetrating into the soil surface that can be varied by varying the tine angle relative to a perpendicular axis to the field surface, varying the depth of the implement, varying driving speed or through various consecutive passes on the same day of cultivation (Cirujeda et al, 2003;Rasmussen et al, 2007). All these setting parameters can be manually or automatically adjusted; however, changing the harrowing intensity by varying the tine angle seems the most appropriate way to develop an automated harrowing system (Rueda-Ayala et al, 2015).…”