This recently-completed 3-year field study evaluated the effectiveness of winter cover crop incorporation and surface gypsum applications relative to conventional fallows for maintaining/improving soil physical properties, stand establishment and crop productivity in a cropping system relying on saline drainage water for irrigation. Six amendment/soil cover treatments were imposed on a rotation of tomato-tomato-cotton as summer crops. Drainage water accounted for about 70% of the total water applied over the course of the experiment. Yields of toamtoes irrigated with saline water were maintained relative to non-saline irrigation in year 1, but were decreased by 33% in year 2. Estimated cotton lint yields of plants irrigated with saline drainage water in 1994, following two seasons of drainage water irrigation, were similar to yields of plants irrigated exclusively with non-saline water. Soil surface crust strength, measured by micro penetrometer was lower in gypsum and cover-crop amended plots relative to saline water irrigated fallow plots during the period of cotton seedling emergence in 1994 in the third year of the experiment. Water stable aggregation was increased following cover crop incorporation relative to saline fallows. Following two seasons of saline drainage water reuse, emergence of cotton seedlings was highest in gypsum-amended plots, but considerably lower in cover crop incorporated plots. Mechanisms accounting for poor establishment following cover crop incorporation may include higher incidences of seed and seedling pathogens in plots where cover crop residues had been incorporated into the soil, and stubble-reinforced surface crusts that resulted in interconnected slabs that impeded timely seedling emergence. These findings and increasing soil surface ECe and SAR values during the course of this study point to the need for special management practices for sustained crop production if drainage water is routinely used.

In environmental circles there are frequent calls to reduce livestock agriculture as a means of improving sustainability of the food system. These appeals are placed upon—and indeed, frequently enflame—an already contentious relationship between environmental communities and livestock industry actors. In this dissertation I peel back some of the layers of this conflict via a focus on California dairy production. California dairy is an important player in recent state efforts to mitigate climate change, so the tense relationship between this livestock agriculture sector and environmental initiatives warrants attention. Understanding the variety of forces at play in the ongoing tensions can help to identify new strategies for mitigating livestock’s environmental impacts. In particular, this research brings attention to social, political, and economic drivers of surplus production as important components of the conflict, underscoring the need for supply management as a solution to both environmental and economic concerns in the industry. It also highlights the potential for new governance policy arrangements to circumnavigate some of the existing tension and implement new environmental initiatives to mitigate climate change.

The objectives of this study, conducted from 2005 to 2007, were (1) to assess the habitat quality of different hedgerow plants for insect natural enemies and pests, (2) to track the movement of insects from hedgerows into adjacent crop fields and (3) to test the effect of hedgerows on parasitism rates of an economically important pest, the cabbage looper (Trichoplusia ni). This study took place at four farms with hedgerows on the Central Coast of California.

Effective ecological management of agroecosystems for both productivity and sustainability is by design a messy and complex task, producing problems which benefit from highly data-focused analyses. Here, three case studies using quantitative approaches to these problems are presented. First, using results from soil nitrogen monitoring in a long-term organic vegetable/strawberry cropping dataset, an ensemble machine learning model and process model are contrasted and used to reveal key drivers of soil mineral nitrogen asynchrony and loss potentials. Environmental factors, nutrient inputs, and management practices interact to determine the magnitude of nitrogen mineralization, and key combinations of these factors, such as early- or late-season disturbance and irrigation, may increase the risk of generating loss-vulnerable pools. Second, a Bayesian network modeling approach is used to synthesize data across multiple lab and field experiments, using cross-experimental data in an integrative manner, furthering our understanding of treatment dynamics in anaerobic soil disinfestation, an ecological soil pathogen control method, and providing a step forward in recommendations to strawberry growers seeking to optimize implementation in their systems. A strong relationship between carbon inputs and soil temperatures suggests that growers may be able to ease environmental restraints with additional inputs during treatment applications. Finally, an unsupervised cluster analysis is applied to a broad survey of on-farm management practices and approaches to disease control in walnut production, detecting two primary groups of divergent management practices. These groups, broadly characterized by moderate versus high levels of data and technology use, utilize markedly different approaches towards the integration of information and technology into on-farm management decisions.

The late 20th and early 21st century have wrought drastic change in the lives and livelihoods of smallholder farmers in the Global South. This research evaluates how rural farming households in Senegal are navigating the intersecting pressures of globalization and environmental change while responding to new opportunities, including the arrival of new technologies. First, I assess farmers’ perceptions of and responses to changes in climate and socioeconomic circumstances, with attention to the factors shaping their adaptive strategies. Second, I evaluate the impacts of aid projects leveraging information and communication technologies (ICTs) and participatory farm trials to incentivize uptake of seeds and fertilizers among farmers. Finally, I follow up with direct beneficiaries of participatory farm trials to gauge post-project impacts on farmers’ production practices, with attention to how new technologies are applied in relation to farm soil fertility gradients. My research shows widespread perceptions of changing weather patterns and shifting socioeconomic circumstances that together undermine the viability of smallholder farming in Senegal. While farmers’ adaptive strategies are differentiated based on their access to resources, I find that youth emigration is playing a growing role in sustaining rural households. My findings further point to limitations and gender inequities in using ICT-enabled extension to disseminate information to rural farmers. Ultimately, farmers in semi-arid parts of Africa face an increasingly risky environment that limits the viability of costly agricultural technologies and increases farmers’ focus on resilience-oriented strategies. These findings provide insight into the future of farming under climate change and suggest ways that development efforts can—and cannot—better support rural smallholder farmers in a changing world.

As climate change presents more and varied challenges for food production, there is a need for novel systems that can balance social and ecological outcomes. No till practices have shown incredible promise providing important ecological benefits, but these systems are still heavily reliant on chemical herbicides and fertilizers and have been limited in adoption to major commodity crops in humid regions without water limitations. Organic agriculture has proven to be a viable production system across a wide range of crops while excluding synthetic pesticides and chemicals that create downstream effects for human and non-human communities. There has been little success in developing the “holy grail” of organic no-till farming, especially for nutritionally important vegetable crop systems in California. I explore the history of organic no till research (Chapter 1), highlighting specific challenges and opportunities from regional syntheses of organic no till production in commodity crops as well as the slowly growing body of literature on organic no-till vegetable production. I then review the results of a 3-year field trial exploring a novel low-reside organic no till production system on yield and nutrient dynamics (Chapter 2). Finally, I explore the cooperative extension service (Chapter 3) and discuss why it has failed to support ecological innovations given its contested history. This work argues that while research on organic no till systems is still at a nascent stage, there are a number of meaningful research pathways to pursue: 1) a focus on basic agronomic challenges, 2) suitability of cover crops and specific cash crop/cover crop combinations, and 3) long-term studies without cash crops to assesses soil physical and chemical properties. Further, given the nature of highly commodified California vegetables, cooperative extension, despite its inconsistent track record, has an important role in supporting newer models of social learning, adaptive research and university/grower partnerships that are needed to support this and future endeavors.

The Vietnamese Mekong River Delta is an epicenter of cultural, environmental, and economic change. New irrigation infrastructure and Green Revolution rice production practice adoption in the 1990s propelled Vietnam into the regional rice market. Simultaneously, renovation policies prompted rural-to-urban migration patterns, with women surpassing men in this trend in 2006. Thus, men are increasingly managing the farm and the family, while women work wage labor jobs in the city to send remittances back home. These changes have influenced many aspects of Vietnamese life. This research explores how these economic, policy, and environmental shifts have influenced the familial relationships and farm practices of the delta.

This dissertation uses a mixed methods approach. Chapter 1 is summative rather than analytical. Chapter 2 uses remotely sensed radar data, combined with in-situ moisture readings, to determine water-saving practice adoption through change detection of a time series wetness index. Chapter 3 is a gender disaggregated plot-level study that uses a binary logistic regression to determine if livelihood approaches on male- and female-managed plots influence adoption of farming practices. Chapter 4 uses a spatial intersectionality approach, a grounded theory, exploring identities and spaces traversed by migrant families in the city and country.

The results of this research paint a nuanced picture of present-day Southern Vietnam. Chapter 2 illustrates a water-saving practice adoption likelihood scale across the delta, indicating promise for the change detection methodology. Chapter 3 finds that gendered plot management is directly associated with SI and CI practice adoption, and there is an indirect gendered impact due to unequal access between the sexes to natural and human capitals that are associated with increased SI adoption. Chapter 4 disrupts assumptions of gender roles by taking a spatial look at intersecting identities. These women and men negotiate a Portable Family identity, based on actions rather than interactions, and oscillating between the urban-productive home and the rural-reproductive home. Chapter 5 points to a trend opposite the “feminization of agriculture” seen across Southeast Asia and parts of Latin America by showing an increasingly male-managed farm.

This research brief explores the apparent conflict between new food safety rules designed to minimize the presence of wildlife around farm fields, and environmental protection efforts designed to decrease the impacts of pesticides, fertilizers, and sediments on the environment.

Using information from existing research, the brief examines the effectiveness of measures being used by Central Coast growers to address environmental problems. We then summarize the history of food safety issues on the Central Coast, and outline potential sources of crop contamination in the field. Finally, we discuss the ways that food safety guidelines conflict with environmental protection methods, proposing the idea that such methods could in fact be designed to reduce contamination sources and improve food safety.

In this research brief we present data from water quality monitoring conducted between October 2000 and September 2004, to demonstrate the way that agricultural land use influences phosphorus concentrations in streams and rivers. We discuss the nature of phosphorus pollution from agriculture along the Central Coast, examine the implications of these data for agricultural regulations, and offer suggestions for reducing phosphorus losses from farmlands.

Agricultural systems are highly complex, due to both inherent characteristics such as emergent processes and transient dynamics, and often high levels of ignorance and uncertainty regarding the relevant system components and interactions. Agricultural systems are also often targeted for change to increase various performance measures or decrease undesired social and environmental externalities. As a result, this complexity is not merely a theoretical issue, but also a practical one, and effective adaptation of these systems requires balancing an appreciation for complexity with the pragmatic goals and constraints of these efforts. This dissertation presents three related interdisciplinary studies that wrestle with this problem in three distinct contexts and for three often-distinct audiences. The first chapter focuses on the field of development studies, where academics, government officials, and members of non-government organizations discuss ways to bring about societal change, often relating to rural livelihoods and non-industrialized nations heavily dependent on agricultural systems. This chapter assesses the discussions among these diverse participants and provides a resolution for semantic entanglements so that the complexity of the problems does not undermine the practical efforts for change. The second chapter is directed towards land managers working in Mediterranean landscapes as they seek to influence land use changes and alternative agricultural practices to increase soil carbon storage. This chapter summarizes the relevant scientific literature and discusses related issues to both inform immediate action and direct future research. The third chapter is a multi-year study in Senegal and The Gambia that uses a network of farmer field trials to test alternative seed and soil management practices within a socially and spatially heterogeneous system. Rather than supporting the current recommendations or identifying alternative “best practices,” these trials identified a range of adaptive options that were comparably effective but varied widely in cost, risks, and availability. This finding encourages farmers to actively explore their alternatives rather then simply adopt official recommendations, and for researchers to support this through more collaboration and less prescription in agricultural research.