SUSWECO - Sustainable weed control in cereals by combining subsidiary crops and minimal soil disturbance

There is a need for more sustainable agricultural production, e.g. farming systems that combine yield objectives with minimized ecological footprints. Two important aspects related to this in cereal production are (i) the use of cover crops to prevent erosion and leaching, and (ii) new methods of weed control with least possible use of herbicides and intensive soil tillage. The SUSWECO project focuses on weed control in cereals with cover crops, especially on perennial weeds such as Cirsium arvense, Sonchus arvensis and Elymus repens. These are a challenge with reduced use of herbicides and reduced tillage. In organic farming, perennials are mainly controlled through intensive soil tillage, which may cause unwanted impacts. Conventional and integrated farming systems have been relying on glyphosate for decades (especially if ploughing is omitted). In the future glyphosate may meet stronger regulations. The goal of SUSWECO is to develop new measures and strategies against weeds without intensive soil tillage and minimal herbicide use. The main objective of the project is to gain knowledge about the long-term effects of cover crops and low-intense tillage on grain yield, weed control and soil structure. Central to this is the continuation of a spring cereal trial in Norway that started in 2019 (the Long-Term Exp.). Results from the experiment have so far shown that the combination of cover crops (perennial ryegrass and clover species) and the use of a prototype tool with minimal soil disturbance, Root-cutter, makes it possible to combine cover crops and mechanical weed control. Results for this combination showed, however, that spring ploughing is necessary to obtain satisfactory control of all perennial weed species and also to kill the winter hardy cover crops without glyphosate. For optimizing treatments in the long-term exp., we started two new field experiments: (i) One with different cover crop seed mixtures in combination with root cutter (+/-). (ii) Another with different numbers of root cuttings (0;1;2) at different soil depths (8 and 16 cm). Until now, no studies have been carried out in winter cereals including combination of cover crops and root cutting. In SUSWECO, during autumn 2024, multi-year experiments were established in Sweden and Norway with cover crop mixture (white clover/Persian clover/black medic) and root cutting. We test in fields if new ‘bioherbicides’ and tools can be part of strategies to kill weeds and overwintering cover crops before sowing new crop in spring. Preliminary results show that ‘bioherbicides’ had poor efficacy, while strategies with harrowing could halve the amount of cover crops and E. repens. As part of machine vision developments to enable spot weeding of perennial weeds in cereals with cover crops, and thereby reduce risk of herbicides and mechanical weeding, drone imagery (DJI Mavic 3 Multispektral) was collected before harvest at low altitude (12 m) in 2023-2024 (experimental fields at Ås). In SUSWECO, energy consumption in various weeding strategies, i.e. comparison of root cutting and ploughing, and the effect different weeding methods have on soil structure, are measured. Measurements of energy consumption have been made in collaboration with the Julius Kühn Institute in Germany. Preliminary results showed approx. 30-40% reduction in diesel consumption for root cutting vs. ploughing. In the Long-Term Exp. soil strength measurements and soil samples were taken for aggregate size distribution and stability analysis after five years (autumn 2023). The soil strength measurements with a penetrometer clearly showed lower penetration resistance in ploughed than in unploughed plots. The penetration resistance was approximately twice as high in unploughed plots where the weeds were controlled chemically or with cover crops compared to corresponding ploughed plots. The difference was smaller where mechanical weed control was carried out. Aggregate size distribution and stability according to the rain method were determined in the laboratory. Aggregate stability was higher in plots with cover crops or with less intensive mechanical weed control (root cutter) that were not ploughed compared to the corresponding ploughed plots. A similar trend was found for several treatments. Ploughing also led to a trend towards a greater proportion of large aggregates (over 20 mm) and a smaller proportion of more desirable aggregate sizes (0.6 to 6 mm). The difference was greatest where no mechanical weed control was carried out. SUSWECO is coordinated by Norwegian University of Life Sciences. It is funded by Forskningsmidlene for jordbruk og matindustri and the project partners Kverneland Group AS, Felleskjøpet Agri and Myhres Maskinomsetning. Inland Norway University of Applied Sciences, Norwegian Institute of Bioeconomy Research, Norwegian Agricultural Extension Service, Swedish University of Agricultural Sciences and Research Institutes of Sweden participate.

Perennial weeds cause major concern in both integrated and organic cereal production due to risk of yield reductions. Control of perennial weeds is primarily done by intensive tillage in organic farming, whereas conventional farming for decades has relied on herbicides as glyphosate, particularly in reduced tillage systems. Glyphosate can soon be restricted or even banned in EU and Norway. Project SUSWECO will develop new weeding tools and strategies for control of perennial weeds in cereals without or with minimized use of herbicides or intensive tillage. Novel tillage tools. root cutters, that cause minimal soil disturbance will make it possible to combine use of subsidiary crops and mechanical weed control. We will test if bioherbicides (e.g. pelargonic acid) and a specially adapted harrow can be parts of strategies killing both subsidiary crop and weeds before new crop is established. Site-specific weed management (SSWM) can significantly reduce environmental loads of uniform chemical and mechanical weed management by applying control measures only at the weed patches in the field. The project will work on machine vision enabling site-specific management of perennial weeds in cereals with subsidiary crops. We will also assess impact on soil quality and energy consumption of selected strategies. We will communicate with end users and stakeholders during project. New knowledge will be disseminated nationally and internationally. SUSWECO is coordinated by Norwegian University of Life Sciences (NMBU). It is funded by Forskningsmidlene for jordbruk og matindustri and the collaborative partners Kverneland Group AS, Felleskjøpet Agri and Myhres Maskinomsetning. Inland Norway University of Applied Sciences (INN), Norwegian Institute of Bioeconomy Research (NIBIO), Norwegian Agricultural Extension Service (NLR), Swedish University of Agricultural Sciences (SLU) and Research Institutes of Sweden (RISE) also participate.