Date of Award

Fall 2021

Project Type

Dissertation

Program or Major

Earth and Environmental Sciences

Degree Name

Doctor of Philosophy

First Advisor

Richard G Smith

Second Advisor

Serita Frey

Third Advisor

Rebecca Sideman

Abstract

Agriculture must adapt to and mitigate multiple environmental crises including climate change, overuse of herbicides, and soil degradation. Cover crops are a promising tool to do so because they protect soil from erosion, increase perenniality (i.e. year-round plant cover) and carbon contributions to farming systems, capture, recycle, and fix nitrogen, and suppress weeds through multiple mechanisms. Terminating high-residue cover crops to produce an in situ mulch for no-till production has added benefits of eliminating the need for tillage, protecting soil against extreme precipitation events and drought, and contributing to weed suppression. However, there are few non-chemical ways to terminate cover crops without tillage. We performed three experiments to investigate whether using reusable plastic tarps is an effective strategy to terminate a winter rye (Secale cereale L)- hairy vetch (Vicia villosa Roth) cover crop and suppress weeds for no-till production. In the first experiment, we studied the difference between clear and black plastic tarps as well as roller-crimping to terminate cover crops and found that black plastic tarps are the most efficacious method, providing significant yield benefits (+58%) to a no-till cabbage (Brassica oleracea var. capitata) crop compared to clear tarps and roller-crimping alone. In the second experiment, we investigated the effects of tillage and tarping in a factorial combination, with and without weed control, on cabbage yields. We found that no-till cabbage following a cover crop terminated with a black tarp produced greater or equal yields to all other treatments. In some years, the weed suppression provided by this system is significant, but weeding enhanced cabbage yields in all years. In the last experiment, we investigated the effects of termination time and termination method (tarping for 10, 20, or 30 days vs. glyphosate or roller-crimping) on ecosystem services including weed suppression and weed community dynamics, cover crop biomass C and N, mulch provisioning, residue decomposition, and N mineralization. We examine these results in two chapters. The first assesses the effects of termination time and method on weed biomass and community dynamics using a community assembly approach. We found that mulch, which is affected by both termination time and termination method, appears to be a strong driver of weed biomass and community, and that both termination time and method can select for weed species based on periodicity. Finally, we examined the tradeoffs between termination time and method on ecosystem services, planting date, and the larger picture of farming systems and environmental consequences of production systems. Differences of 10-20 days termination time significantly affected cover crop biomass, which ranged from <4 Mg ha-1 at the first termination time at one site to nearly 8 Mg ha-1 at the third termination time at another site. The effects of termination time on cover crop biomass were especially pronounced for the vetch component of the rye-vetch mixture, which doubled between the first and third termination times at both sites. Although cover crop biomass quantity and quality (C:N ratio) were drivers of ecosystem services in these systems, termination method and resulting crop planting dates also played a significant role.

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