Abstract
The adoption of conservation agriculture (CA) techniques by farmers is changing the dynamics of weed communities in cereal fields and so potentially their spatial distribution. These changes can challenge the use of site-specific weed control, which is based on the accurate location of weed patches for spraying. We studied the effect of two types of CA (direct drilling and harrow-tilled to 20 cm) on weed patches in a three-year survey in four direct-drilled and three harrow-tilled commercial fields in Catalonia (North-eastern Spain). The area of the ground covered by weeds (hereafter called “weed cover”) was estimated at 96 to 122 points measured in each year in each field, in 50 cm × 50 cm quadrats placed in a 10 m × 10 m grid in spring. Bromus diandrus, Lolium rigidum, and Papaver rhoeas were the main weed species. The weed cover and degree of aggregation for all species varied both between and within fields, regardless of the kind of tillage. Under both forms of soil management all three were aggregated in elongated patterns in the direction of traffic. Bromus was generally more aggregated than Lolium, and both were more aggregated than Papaver. Patches were stable over time for only two harrow-tilled fields with Lolium and one direct-drilled field with Bromus, but not in the other fields. Spatial stability of the weeds was more pronounced in the direction of traffic. Herbicide applications, crop rotation, and traffic seem to affect weed populations strongly within fields, regardless of the soil management. We conclude that site-specific herbicides can be applied to control these species because they are aggregated, although the patches would have to be identified afresh in each season.
Highlights
Weeds are one of the most significant threats to crop production worldwide
Agronomy 2020, 10, 452 the reduction of grain crop yield due to competition by the major winter annual grass weeds such as Lolium rigidum, Avena sterilis, and Bromus diandrus and broad-leaved weeds such as Papaver rhoeas is the main concern of the farmers
The three most important weeds were Lolium rigidum, Bromus diandrus and Papaver rhoeas, and we focus on them in our analyses
Summary
Crop losses in yield and quality due to weeds, as well as costs of control, have a significant economic impact on crop production. In Australia, Llewellyn et al [1] reported that weeds in their Mediterranean climate area cost Australian grain growers $100/ha in expenditure and losses, with an average expenditure estimated at $75/ha, including herbicide and non-herbicide practices. We know of no data on economic impact of these weeds on the crops of this region, but yield losses in cereals have been quantified to be as large as 85% for severe infestations (1000 plants/m2 ) of Lolium [2], 50% for infestations of more than 300 panicles/m2 of Avena [3] and 71%. Papaver has been reported to reduce crop yields between 6% and 70%, depending on crop density, degree of infestation and season [5]
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