"Perennial Crops As Leverage Points in Agroecosystems".

As the volatility and intensity of weather patterns increase under global change, diversifying cropping systems with perennial plant species may offer one means of buffering against these events. Because the phenology, life history and physiology of perennial crops contrast strongly with those of the annuals that currently dominate much of the agricultural landscape, they are likely to exert outsized influence, with the potential for leveraging both positive and negative effects at the agroecosystem level. In this presentation, I will use effects on weed management as a frame of reference for examining potential impacts of diversifying with perennials in two contrasting study systems. First, in a long-term study in Boone, IA, lengthening a corn-soybean (2-yr) rotation to include oat underseeded with alfalfa, followed by an alfalfa phase (4-yr), provided strong weed management benefits by disrupting weed life cycles, suppressing weed germination and preventing seed return. This resulted in negligible weed biomass and similar rates of weed seedbank decline in the 2 and 4-yr systems, while achieving large reductions in the amount of herbicide applied and ecotoxicity in the 4-yr system. The second example consists of quantitative risk analysis of the potential for perennial bioenergy crops to escape cultivation and become invasive. Consideration of such risks prior to widespread deployment of bioenergy feedstock crops can help generate management guidelines for their safe production. Viewing perennials as potential leverage points in cropping systems may aid their judicious application to maintaining and enhancing cropping system performance in a changing climate.