Reducing Tillage and Herbicide Use: Can Weed-Induced Crop Yield Losses Be Limited?
Photo: Agroscope
Integrated weed management with reduced tillage and reduced herbicide inputs can successfully control weeds in wheat and prevent yield loss.
The Swiss Confederation’s action plan on plant protection products aims to reduce herbicide use. This can be achieved through integrated weed management (IWM) based mainly on a combination of preventive and curative measures. The lower the tillage intensity, especially no-plough strategies, the more difficult it is to reduce herbicide inputs.
Testing five integrated weed management strategies
Five different integrated weed management strategies with different levels of tillage intensity and herbicide use are being tested in a field trial based on a six-year crop rotation (2020‑2025) at the Agroscope Agricultural Research Station in Changins:
- annual ploughing without herbicide use
- annual ploughing with reduced herbicide use
- occasional ploughing (roughly every three years) with reduced herbicide use
- shallow tillage (max. 10cm depth) without herbicide use
- direct sowing with reduced herbicide use.
The objective is to measure the effects of these strategies on weed biomass (proportion of weed biomass relative to total aboveground plant biomass in %), weed density, weed species richness and crop yield.
Comparable yields can be obtained with the five integrated weed management strategies
Winter wheat and its preceding crops (soybean and barley) were grown from 2020 to 2022. During the three-year trial period, all tested strategies successfully controlled weeds and comparable yields were achieved. 2020 was the only year in which a moderate weed-related yield reduction in wheat was observed.
Ninety-one weed species were identified, with low weed densities observed in autumn and winter. The dominant weed species recorded were shepherd’s purse (Capsella bursa-pastoris), chamomile (Matricaria chamomilla), common field speedwell (Veronica persica) and goosefoot species (Chenopodium sp.). No differences were found between the tested strategies in terms of weed biomass (median < 8%) and the number of weed species (median < 20). However, in strategy 1 (ploughing without herbicide use) weed density increased over the trial period by an average of five plants per m2 each year.
Reduced herbicide use requires more intensive tillage, and vice versa
The indicator ‘herbicide use’ is quantified by the herbicide treatment frequency index (HTFI), which calculates the quantity of herbicide used based on the permitted application rate and the treated area. The indicator ‘tillage intensity’ is quantified by the soil tillage intensity rating (STIR). The higher the STIR value, the more intensive soil cultivation is. HTFI and STIR developed in inverse proportion in the tested strategies, i.e. tillage intensity increased over time when no herbicides were used. In contrast, more herbicides had to be applied with reduced soil cultivation.
Weeds can be controlled successfully in wheat through different combinations of measures. The key is not to adhere to rigid cultivation practices but to respond flexibly to the situation, soil conditions, weather, etc.
Conclusions
- In wheat, weeds can be successfully controlled through integrated weed management with reduced herbicide inputs and/or reduced tillage with less ploughing.
- A moderate weed-related yield reduction was observed in only one of the three trial years.
- In the herbicide-free strategies, the intensity of soil disturbance increased over time.
- In the direct sowing strategy, an increase in herbicide input was observed over the years.
- For effective weed control, different measures must be combined in addition to a diverse crop rotation.
Bibliographical reference
Reducing tillage and herbicide use intensity while limiting weed-related wheat yield loss.
