Adapting agroecosystems to water scarcity: Dry farming and crop rotation as transitions to diversified farming systems in California and the US Midwest

As climate change gives rise to water shortages and unstable growing conditions in California and across the United States, agricultural systems must be able to adapt to increasingly extreme environmental stressors. Diversified farming systems, which incorporate biodiversity across multiple temporal and spatial scales to support ecosystem services, offer an alternative to the fragility of the current industrialized regime that dominates US agriculture. When small-scale, thought-intensive, diversified farming systems are supported by research and socio-political movements that defend them and advocate for their wider adoption, food production will transition towards a science, practice, and movement known as agroecology. While many argue that agroecological transitions are necessary to achieve stable food production and climate, economic, and political justice in the US agricultural system, state and federal policies do not reliably support diversified farming systems. In order to craft effective policy interventions, we must have an intimate knowledge of how and why diversified farming practices work to properly support their success and spread. In my dissertation I explore two regional examples of diversified farming practices and their potential for wider adoption given current and possible future policy landscapes. In corn-based crop rotations in the US Midwest and tomato dry farming on California’s Central Coast, climate shocks have sparked a need for dramatic change, opening an opportunity for policy to guide agriculture towards an agroecological future. With the help of farmer collaborators, I ask how each of these systems functions, how policy has failed them, and where it may yet succeed./nThe first chapter of my dissertation examines the political and physical landscapes in which farmers grow corn-based rotations in the US Midwest, asking what factors lead farmers towards complex vs simplified rotations. I used publicly available, remotely sensed datasets to look at relationships between rotational complexity, and biophysical (land capability, precipitation) and policy-driven (distance to the nearest biofuel plant) factors on 1.5 million fields in the region, using bootstrapped linear mixed models to account for spatial autocorrelation. I found that policy and economic incentives continue to lead farmers towards simplified crop rotations, such as corn-soy and even corn monoculture. In particular, amidst already elevated corn prices from crop insurance structures and livestock feed, I saw that proximity to biofuel plants–where corn prices tend to be higher due to the federal biofuel mandate–encourages farmers to grow corn in as many years as possible. These policy and economic factors then play out in biophysical landscapes as well, where fields with the highest quality soils and precipitation–which can tolerate degradative soil practices without compromising yields in the near term–tend towards the most simplified rotations./nThe second and third chapters of my dissertation explore diversified farm management on California’s Central Coast in dry farm tomato systems, which rely on diversified farming practices (cover cropping, compost application, organic management, etc.) to build soil water holding capacity and fertility. Dry farming allows farmers to grow produce with little to no irrigation water, relying instead on water held in soils from winter rains to support crops through rain-free summers. As climate change increases water scarcity in California, farmers, advocacy groups and policymakers have begun looking to dry farming as a potential solution to the state’s overextended water budget. However, little research has been done on vegetable dry farming in the state, and no coordinated effort has been made to understand the policy conditions that would allow vegetable dry farming to thrive./nIn my second chapter, I collaborated with six dry farm operations in a participatory process, coming up with research questions that the farmers who most intimately understand tomato dry farming were eager to answer. After a season of intensive soil and harvest sampling on seven dry farm fields on California’s Central Coast, we were able to come to a better understanding of how the system functions, and develop concrete management suggestions for farmers to consider. We found that, due to quickly drying surface soils, harvest outcomes were only impacted by nutrients below 30-60cm in the soil profile, upending soil fertility management paradigms on irrigated fields, where focus is almost entirely on the top 30cm of soil. We were also able to caution against arbuscular mycorrhizal fungal (AMF) inoculants, which have been marketed to farmers with increasing intensity but, if anything, harm harvest outcomes in dry farm systems (as opposed to resident AMF communities, which are fostered through diversified management and typically improve harvest outcomes). Lastly we showed that dry farm soils develop a signature in their fungal communities that supports fruit quality, suggesting that farmers would likely benefit from developing full dry farm rotations where soils are kept irrigation-free for multiple years./nIn my third chapter, I conducted semi-structured interviews with the same farmers who participated in the field study to better understand the full context in which tomato dry farming operates on the Central Coast. As farmers, researchers, and policymakers consider an expansion of dry farm vegetable production in California, I wanted to ask how farmers understand the practice and what its environmental and economic constraints are. I emerged with a synthesis of farmer-stated environmental constraints that I used to create a map of California cropland that could be suitable for future dry farm production. As I considered an expansion of dry farming onto these new lands, I drew on farmers’ experience to explore how to maintain dry farming’s history as an agroecological alternative to the industrial style of farming that dominates the region. Farmers had a clear message about the small operations and direct-to-consumer marketing styles that have been the foundation of dry farming success, and that must serve alongside soil health practices as a model for an agroecological transition towards water savings in California. I identified policies such as publicly funded demonstration farms, participatory breeding programs, and public procurement that could promote dry farm expansion while preserving its fuller context and identity, rather than stoking a shift toward an industrial cooptation of the practice that could edge small growers out of dry farm markets./nTaken together, this dissertation follows on-farm diversification practices–especially those that can help farms guard against water scarcity–through an arc of past and possible future policy. I ask how policy has discouraged crop rotational complexity, and how policy might foster an environment in which dry farming could thrive as a model for an agroecological transition towards water resiliency. I strive to understand dry farming through the eyes of those who practice it to make management and policy recommendations that are grounded in deep knowledge of the system. Through these examples of how complex ecological and policy interactions play out in two separate regions, I highlight the resilience and importance of diversified farm systems, and the possibilities and pitfalls in policy interventions that attempt to prepare our agricultural system for changing climates.

Advisor: Bowles, Timothy M