Hannah’s mentorship has been invaluable at inflection points in my PhD process, and I can’t overstate how lucky her new grad students will be to have her as an advisor. I feel incredibly privileged to have the community support of more people than I can thank individually without making my acknowledgements longer than my dissertation. Communities that have given me particular encouragement, joy, and solace include the 2018 ESPM cohort, Friendship Village, the Sunset/Pomona/floating/CCST crew, my Park Palace queens, my sweet childhood friends, and every last Sheline and Socolar. You all make me feel connected to something I want to be accountable to. Within these communities, a few people stand out as being particularly instrumental in helping me thrive throughout this PhD. The folks at Rat Village–Abby, Alli, Brendan, and Charley–made a beautiful house into a beautiful home. You taught me how organization and communication can create abundance, and gave new meaning to what it can mean to live communally. Everything from fridge leftovers to card nights to casual kitchen encounters carried me through this experience, and I hope you will see my use of the term “Rat Village” in my dissertation as indicative of the lengths I am willing to go to to express my gratitude. Two dear friends, Erin Curtis Nacev and Claire Woodard, flood drain tray have been cornerstones of my PhD experience. They were both my gateway to the Bay Area–I would never even have arrived here if Berkeley hadn’t felt like the homecoming that you created.
Through med school, residency, and raising a child, Erin found time for visits and calls, and is my–and perhaps the entire world’s–best model for what a can-do attitude can be. She is generous, loyal, principled, a source of such joy, and capable of everything. Plus she and Zach made Evie, which is really the highest praise you can give a person. Of the narratives I have watched unfold over the course of my PhD, few have made me happier than watching Claire transform from the best of friends to the best of collaborators. It was her overwhelming loyalty as a friend and endless capacity for hard work that brought her to my first tomato field, and my own incredible luck that has kept her farming ever since. I marvel that the person I’m most likely to call crying on the phone is the same person I’m most likely to call about transplanting techniques. Claire’s accompaniment through this entire experience has been so thorough that it’s alarming to remember there was a time before Claire was a farmer, and to imagine what my field seasons would have looked like without her there. I have also been lucky to have the deep support of many family members on this journey. That my brother, sister-in-law, and sister-cousin all had PhDs when I arrived at Berkeley meant that my PhD did not have to be demystified, but rather was never mystified in the first place. Jacob, Bethanne, and Annelle’s guidance, encouragement, and commiseration have been the sweetest set of bumper rails as I ricocheted through this experience. Jacob in particular has fielded enough “hi how are you, but actually can we talk about statistics?” phone calls from me that you might think “random effect” is a family member we desperately need to gossip about. Luckily my niece, Isabelle, has been the most brilliant distraction when things get too heady–my heart remembers to refocus when I see her shining eyes. Though none of my grandparents are here to read this dissertation, I can see the way their faces would beam if I could show it to them. Their influences are almost comically obvious in my career choices–Grandpa Ray’s determination and proclivity for natural sciences, Grandma Yvonne’s steadfast commitment to social justice, Grandpa Milt’s philosophy and politics, and Grandma Molly’s effortless ability to connect to everyone she met.
From antiracism to interviews, DNA work to policy ideas, they have created a foundation that I want to build on, and their obvious pride in me has given me the confidence to start building. For my mom and dad, I reach the limits of what I know how to do with words. To say that your love and support for me was unwavering suggests the possibility that it might have wavered, and the knowledge that that is not possible is baked into the bedrock of my existence. You are the people I want to consult with every conundrum that comes my way, and the people who most celebrate my every success. Dad, you know it’s not possible to fill the space Mom left in our lives, and you fill every space around that. My luck at having Varun, my partner, in my life can be measured in the mornings I wake up happy, my growing ability to process out loud , the days my grump melts into grins, the times I go backpacking, the plants in our living room, the edited drafts of each chapter below, the width of our couch, and the number of dissertation-fueling treats in our cupboard. He is patient, joyful, loving, smart as all get-out, and an inspiration to me. His curiosity has brought a new perspective to the work I do, and I can navigate my decisions more clearly in the paths he reflects back to me. Varun, you extend yourself to nurture my growth, and you can see that growth written in these pages. I want to be with you everywhere. My final gratitude is to the land that made this work possible and its generations of stewards. These soils continue to inspire, feed, and live through millennia of care, and I am indebted to those who built relationship with these places. I want to acknowledge and pay my respect to the Awaswas speaking Uypi Tribe and Chochenyo-speaking Ohlone people, whose unceded territory encompasses the field sites and laboratories where this work took place. My work has benefited from the occupation of this land, and thus, with this land acknowledgement, I affirm Indigenous sovereignty.Over 70% of the 62 million ha of cropland in the Midwestern United States is grown in corn-based rotations. These crop rotations are caught in a century-long simplification trend despite robust evidence demonstrating yield and soil benefits from diversified rotations. Our ability to explore and explain this trend will come in part from observing the biophysical and policy influences on farmers’ crop choices at one key level of management: the field. Yet field-level crop rotation patterns remain largely unstudied at regional scales and will be essential for understanding how national agricultural policy manifests locally and interacts with biophysical phenomena to erode— or bolster—soil and environmental health, agricultural resilience, flood and drain tray and farmers’ livelihoods. We developed a novel indicator of crop rotational complexity and applied it to 1.5 million fields across the US Midwest. We used bootstrapped linear mixed models to regress field-level rotational complexity against biophysical and policy-driven factors. After accounting for spatial autocorrelation, there were statistically clear negative relationships between rotational complexity and biophysical factors , indicating decreased rotation in prime growing areas. A positive relationship between rotational complexity and distance to the nearest bio-fuel plant suggests policy-based, as well as biophysical, constraints on regional rotations. This novel rotational complexity index is a promising tool for future fine-scale rotational analysis and demonstrates that the United States’ most fertile soils are the most prone to degradation, with recent policy choices further exacerbating this trend.Biological simplification has accompanied agricultural intensification across the world, resulting in vast agricultural landscapes dominated by just one or two crop species. The Midwestern US is a prime example1, where corn currently dominates at unprecedented spatial and temporal scales. An area the size of Norway is planted in corn in the Midwest in any given year with little variation in crop sequence; over half of Midwestern cropland is dedicated to corn-soy rotations and corn monoculture. Directly and indirectly, this agricultural homogeneity causes environmental degradation that harms ecosystem health while also contributing to climate change and increasing vulnerability to climate shocks. Agricultural diversification in space and time reverses this trend towards homogeneity with practices like crop rotations that vary which harvested crops are grown in a field from year to year.
Crop rotations are a traditional agricultural practice with ample evidence that complex rotations— ones that include more species that turn over frequently—benefit farmers, crops, and ecosystems. As one of the principles underlying agricultural soil management, diverse crop rotations promote soil properties that provide multiple ecosystem services including boosting soil microbial diversity, enhancing soil fertility, improving soil structure and reducing pest pressu. These soil benefits combine to increase crop yields and stabilize them in times of environmental stress. Crop rotations’ environmental and economic benefits typically increase with the complexity of the rotation , while conversely, biophysical aspects like soil structure and microbial populations are degraded as rotations are simplified. Despite its benefits, crop rotational complexity continues its century-long decline in the Midwestern US. Corn-soy rotations increasingly dominate over historical crop sequences that included small grains and perennials, with corn monocultures also on the rise. This increasing simplification is in part the result of a set of interlocking, long-standing federal policies aimed at maximizing production of a handful of commodity crops that distort farmers’ economic incentives. Regional rotation simplification is clear from analyses of crop frequency, county-level data, and farmer interviews. However, fine-grained patterns that more completely reflect farmers’ rotational choices across the region, and how those choices relate to influences from policy and biophysical factors that play out across agricultural landscapes, remain largely unstudied. This knowledge is essential for understanding how national agricultural policy manifests locally and interacts with biophysical phenomena to erode—or bolster—soil and environmental health, agricultural resilience, and farmers’ livelihoods. Bio-fuel mandates and concerted efforts to craft industrial livestock systems as end-users of these corn production systems make corn lucrative above other commodities, while federal crop insurance programs push farmers to limit the number of crops grown on their farms. These policies, along with the current corporate food regime, drive pervasive economic incentives to grow corn, and farmers must increasingly choose between growing corn as often as possible to provide a source of government guaranteed income, and maximizing soil benefits and annual yields through diversified rotations. These policies both alter agricultural economics at a national level by boosting corn prices and manifest locally in grain elevators and bio-fuel plants that create pockets of high corn prices with rising demand closer to each facility. Biophysical factors like precipitation and land capability that are highly localized and spatially heterogeneous can catalyze or impede this simplification trend. For example, increasing rotational complexity is one strategy that farmers may employ to manage marginal soils or greater probability of drought, while ideal soil and climate conditions allow for rotation simplification to be profitable, at least in the short run. As these top-down and bottom-up forces combine, we ask: how do farmers optimize crop rotational diversity in complex social-ecological landscapes, with top-down policy pressures to simplify intertwined with bottom-up biophysical incentives to diversify? Because biophysical factors and even policy influences vary greatly at the field scale at which management decisions occur, an approach is needed to assess patterns of crop rotation that can capture simplification and diversification at this scale. Though remotely sensed data on crop types can now show fine-scale crop sequences, previous approaches to quantifying rotational complexity have relied on classifying rotations based on how often a certain crop appears in a region over a given time period, aggregating over large areas, or examining short sequences. To date, methods to capture rotational complexity have therefore been unable to address management decisions at the field scale , and/or lose valuable information about the number of crops present in a sequence and the complexity of their order . At the other end of the spectrum, farmer surveys have impressively detailed the economic and biophysical considerations that go into farmers’ rotation decisions, yet are limited by the number of farmers they can reach and who chooses to respond. Here, we explore how aspects of farm landscapes influence field-scale patterns of crop rotational complexity across the Midwestern US. We developed the first field-scale dataset of rotational complexity in corn-based rotations, covering 1.5 million fields in eight states across the Midwest and ranking crop sequences based on their capacity to benefit soils. We examined rotations from 2012-2017 to coincide with the introduction of the Renewable Fuel Standard, or “bio-fuel mandate,” which took full effect in 2012.