Harnessing Forage Mixtures to Increase Ecosystem Services of Arthropod Predators and Weed Suppression

View the project final report

Commodities

• Agronomic: corn, sorghum sudangrass, soybeans, sunflower

Practices

• Crop Production: cropping systems, intercropping, multiple cropping, varieties and cultivars
• Natural Resources/Environment: biodiversity
• Pest Management: biological control, cultural control, integrated pest management, weed ecology

I aim to use forage crop mixtures to alleviate intensive inputs required by, and reduced biodiversity associated with, monocultures. Increasing plant species diversity in a cropping system can maintain or even increase crop productivity while improving ecosystem services, like arthropod predation and weed suppression. Using a combination of field and greenhouse experiments, I will study the productivity of forage mixtures and quantify one key ecosystem service that can be improved with species mixtures: weed suppression. Mixtures should help suppress weeds by two mechanisms, first, by increasing populations of weed-seed predators like ground beetles (Carabidae), and second by direction competition with weeds. In field experiments with mixtures of different complexities, I will track populations of weed-seed predators and characterize the weed seeds they prefer. I will also measure weed suppression associated with increased species diversity, and shifts in weed community composition as driven by functional groups of crop species. I will ultimately use these results to help farmers adopt forage crop mixtures rather than monocultures. My data will help farmers better predict weed emergence from their seed bank, better control weeds in forage crops and reduce or be more selective with the types of herbicides they use. This research will also influence a broader community via field days, international meetings, outreach events and publishing on website platforms and in peer-reviewed journals.

Objective 1: Determine how species diversity within crop mixtures can influence arthropod communities, particularly weed seed predators. Research has established that increased plant species diversity maintains a more stable community, is more productive, and provides additional habitats for animals. These additional niches allow greater diversity of arthropod species to inhabit crop mixtures compared to monocultures. I expect arthropod abundance and diversity, specifically weed-seed predators, to increase as crop mixture diversity increases, and increase weed suppression. If weed-seed predators show no preference for broadleaf and grass weeds, I expect weed functional groups to be suppressed equally and increased crop species diversity in mixtures will only increase the rate of consumption, but not alter the composition.

Objective 2: Determine how functional groups within crop mixtures can shift or suppress weed composition. I will test functional groups (grasses, broadleaves) in mixtures of forage crops to determine their influence on the weed community. I will measure both composition, the proportion of grass and broadleaves, and suppression, the total number of weeds. Because of planting density, herbicides and optimal timing and depth for rapid germination, I expect the forage crops to outcompete, and therefore suppress, weed populations of the same functional group. Consistent with my preliminary results, I expect grass forage crops to better suppress grass weeds, shifting the weed community to comprise more broadleaf weeds and the opposite for broadleaf forage crops.

Objective 3: Determine how an increase in weed seed predators and selective suppression of functional groups ultimately influences the number and composition of weeds in forage crop mixtures. I aim to quantify interactions of the first two objectives to determine the ultimate result of weed community suppression and composition. The dominant functional group of the forage mixture, regardless of the number of species, is likely to shift the weed composition. However, increased number of forage species is expected to increase the rate of consumption by weed-seed predators and therefore suppress overall weed abundance. By evaluating these interactions, I will identify which pressure, the functional group or the number of crop species, drives the weed community.

Objective 4: Quantify productivity of forage mixtures and tradeoffs among input costs, yield and quality. I will quantify forage yields to compare biomass, quality and determine gross profit. Input costs, including herbicides, will be used to calculate net return, quantify economic value of weed control and compare input and net return for each forage mixture.