7: Pairing down the effects of plant architectural complexity on organic urban food production

Johnson County in Arkansas is designated as a “food desert” by the USDA, meaning households lack access to fresh, affordable food. Community gardening is an attempt to mitigate this shortage, a source of income for others, as well as an educational opportunity.           

Integrated pest management (IPM) may be a viable alternative to pesticides. Natural enemies may prefer diverse plant habitats with architectural complexity compared to simpler habitats. In 2018, we determined the influence of plant diversity and complexity on IPM in a garden setting. Plantings of Swiss chard (monoculture treatment) and Swiss chard, tomato, kale, and beans (polyculture) were compared. We added barriers of non-crop plants to increase complexity compared to wood chips. Species diversity and herbivore abundance were compared. We recorded chlorophyll fluorescence, content, and plant yield. In 2019, we conducted a smaller study standardizing the more effective wood chip treatment to isolate the effects of monoculture and polyculture.

In 2018, we found greater natural enemy diversity in monoculture plots, greater herbivore diversity in polyculture plots, and those surrounded by green manure. Plants had higher chlorophyll content, fluorescence, and yield when planted next to wood chips. The 2019 results support community relationships. 

Our findings in a small-scale horticultural system suggest that microclimates created by a matrix of wood chips may be more protective and provide better refuges for natural enemies. Wood chips may better retain moisture and buffer temperature extremes compared to green manure. Additionally, prey abundance in polyculture may be too scarce to support natural enemies.