Organic farmer mental models: Associations between weed seedbanks and management philosophies on New England farms

Background/Question/Methods

Organic agriculture is a rapidly increasing sector globally, and serves as a broad systems-based approach to conserving both biodiversity and ecosystem functions while providing healthy food. Although weed management is a major challenge for organic farmers, we know little about why farmers do or do not decide to use ecological approaches to manage weeds. We interviewed 23 organic farmers in northern New England about their weed management knowledge and philosophies. Interviews were recorded, transcribed, and coded to yield a qualitative data set for construction of farmer mental models to compare with expert educator mental models. To characterize weed pressure on each farm, we collected soil samples from 5 fields at each farm (115 fields total) and measured by germinable weed seedbank density. The main objective of this study was to assess whether farmer knowledge explains variation in weed pressure on their farms. 

Results/Conclusions

Weed seed density per farm ranged from 2,775 seeds per m-sq to 24,678 seeds per m-sq to a soil depth of 10 cm. Evenness and diversity varied across the 23 farms, and the most uneven seedbank communities were consistently dominated by crabgrass Digitaria species. In the interviews, farmers most often reported hairy galinsoga Galinsoga ciliata and crabgrass as their most problematic weeds. The proportion of these two most problematic weeds in each farm’s seedbank ranged from 0 to 73% of total weed seed density. Both total seed density and proportion of problematic weeds were associated with key interview variables. The number of mentions of “risks of weeds” by farmers was negatively associated with weed seed density, such that farmers who had lower weed seed densities mentioned agricultural risks of weeds, such as biological competition and harvest interference, more frequently. Greater knowledge of ecological weed management was associated with a smaller proportion of problematic weeds. In summary, farmer knowledge explained a significant component of the variation in weed seedbank densities. Targeted education efforts could potentially lead to improved success of ecological weed management in the future, thus decreasing labor costs and time necessary for farmers to manage weeds.