This alternative outcome here suggests that while this soil chemical property shows sensitivity to differences perceived by farmers in their selected fields, this commonly used indicator does not adequately capture the direction of farmer knowledge of soil fertility between their selected fields. On the one hand, it is not surprising that total soil nitrogen was the only soil indicator able to detect differences between farmer-selected “most challenging” and “least challenging” fields, especially given that after nearly a century of research total soil nitrogen remains one of the most predictive measures of soil fertility status . However, the contradictory direction of our results for total soil nitrogen between farmer-selected “most challenging” and “least challenging” fields emphasizes that current scientific application of this soil indicator does not readily transfer for use on-farm. One potential reason for this inconsistency may be because as a soil indicator, total soil nitrogen reflects both the amount of chemically stable organic matter and more active organic matter fractions, and therefore gives a rough indication of nitrogen supplying power in the soil. However, in practice it is possible that fields deemed by farmers as “least challenging” have depleted their nitrogen supplying power due to more frequent crop plantings, for example— compared to fields that are “most challenging” and therefore may be less frequently planted with crops throughout the year. This finding underscores the current lack of interpretation of soil test results in community with both agricultural researchers and farmers present together; the current gap in interpretation of soil testing results was repeatedly emphasized by farmers during interviews, and suggests that— moving forward, seedling grow rack contextualizing and interpreting soil test results in local farming contexts is key to disentangling potential mismatches between farmer knowledge systems and agricultural researcher knowledge systems.
To move toward this outcome requires deep listening and relationship building on the part of agricultural researchers not currently widely applied .Whereas another similar study found that active carbon was the singular most sensitive, repeatable, and consistent soil health indicator able to differentiate between fields in their study on organic farms in Canada , we highlight that one potential reason for this difference in our results might be as a result of differences in management in each study. While our study consisted of farms along a gradient of organic management , the prior study focused on three organic farms with similar management. This divergence in results highlights the importance of accounting for a gradient in management when evaluating the efficacy of soil health indicators on working farms. Much remains to be learned about how inherent soil properties and dynamic soil processes interact with complex management systems on working farms . Limited prior research that has looked at the effects of multiple soil management practices indicates that metrics for soil health are a product of both inherent soil properties and dynamic soil properties . Whether available soil indicators could translate these soil properties and processes when management systems are complex remains unclear. As an added layer of complexity, field variability is hard to distinguish from management-induced changes in soil properties . To address this challenge, prior studies have suggested increasing samples, the number of sites, and sampling strategies that account for spatial and temporal variability ; however, as farmers themselves expressed in this study, such an approach requires additional time and resources, and may not increase their utility—at least to farmers—in the end.
In this sense, farmer knowledge may serve as an important mechanism for ground-truthing soil health assessments, particularly when management is synergistic and does not rely heavily on organic fertilizers. As emphasized by our results above, farmer involvement in soil health assessment studies is imperative to better converge soil indicators with farmer knowledge of their soil. Lastly, our results also highlight the utility of incorporating information about nitrogen-based fertilizer application on sampled field sites, particularly when assessing soil indicators on working farms with a large variation in the quantity of N-based fertilizers applied . Farms on the low end of additional organic fertilizer application showed minimal differences between farmer selected fields for soil fertility, particularly in terms of soil inorganic nitrogen —which suggests that differences in soil fertility in fields with more circular nutrient use may be less detectable using commonly available soil indicators. This cursory finding here corroborated farmer observations touched on in the previous section above, and requires further investigation to see if similar trends extend to other organic systems.In this dissertation, I have shared a small slice of farmer knowledge of soil from a region of northern California that represents a central node of the organic movement in the United States. I have also attempted to intersect this knowledge system with agricultural researcher knowledge systems of soil. Not surprisingly, I found that the frame of reference used among farmers in this dissertation mapped out quite differently from the frame of reference used among agricultural researchers that collaborated on this work. Of course, this broader conclusion is not to say that farmer knowledge bases of soil and agricultural researcher knowledge bases of soil did not overlap at all; indeed, the two ways of knowing had much in common, as outlined in Chapter 3. However, stepping back—as a person who was not born in the US and for whom English is not their first language—I see part of the divergence in knowledge systems among the two groups as partially stemming from a lack of a shared language .
While I am not in any way suggesting that both knowledge bases be “watered down” to a universal language that strips away the richness of each knowledge base, I am suggesting that careful translation between the two knowledge bases is needed to work toward a common language. Through my informal conversations with the local cooperative extension advisor in this region of northern California , this need for a shared language among diverse agricultural stakeholders is also surfacing among her communities and networks as well. Exactly what this shift looks like in academic research practice and within the academic research process is still unfolding and in emergence as I write these words. It is clear, however, that this shift should not be delegated to science communicators and/or extension advisors as their responsibility alone; and moreover, such a shift requires fundamental change in current research frames. In this dissertation, I have provided an offering to the collective murmurations of this critical need in agricultural research that is slowly resurging. So, in addition to widening our frame of reference as academic researchers in agriculture, there is also a need to work toward a shared language with other non-academic researchers—most imminently, farmers. Engaging in such a process can only further widen our frames as academic researchers in agriculture; ideally, greenhouse growing racks the hope is that we might widen our frames and enlarge our capacity for richer language and mutual understanding so much that we are collectively rewired to allow other ways of knowing into the academic lexicon of agricultural research. I have learned so much from these farmers with whom I had the honor and privilege to interact with through this dissertation work. But, if I had to elevate one nugget of wisdom that nearly every farmer always seemed to circle back towards—that was the power of listening, of observing, of being tactile, of tasting, of smelling, and of being in reciprocity to their particular milieu. Through such embedded, sensorial exchange, we can invite a multiplicity of perspectives and reanimate what is considered academic research in agriculture, and more importantly, how academic research in agriculture is carried out. In weaving together distinct perspectives and different voices, we can enlarge the whole and rewire the largely monochromatic traditions of agricultural research. In this process of rewiring, it is my modest hope that agricultural researchers can move towards creating a more textured and more complicated understanding of agricultural systems. I look forward, backward, inward, and outward to the unfurling of this hope.With its Mediterranean climate of moist, mild winters and dry moderate summers, a broad range of fruit and vegetable crops can be grown year round on the central coast of California. Monterey and Santa Cruz counties combined produced $912 million gross value of strawberries and over $2.7 billion worth of vegetables in 2011 . As the interest in organic farming and the demand for organic produce has increased during the last decade, organic farming on the central coast has also greatly increased. There were over 9,300 certified organic hectares in Monterey and Santa Cruz Counties in 2011, five times the number recorded in 1998 . The total farm gate revenue from organic farming in these counties was over $197 million in 2011, representing a dramatic 12-fold increase in 13 years . This trend is also true for organic strawberry production. In 2000, 77 ha of organic strawberries were grown in central coastal California, but by 2012 this had increased to 509 ha, representing 8.3% of the total strawberry production in the area .
Continued growth of organic strawberry production in this area, however, faces the challenge of managing soil-borne diseases without the use of synthetic fumigants and fungicides. Verticillium wilt is a soil-borne disease caused by Verticillium dahliae that can damage a wide range of important crops in California. Host crops include lettuce, tomatoes, potatoes, apples, cotton, artichokes, and strawberries . Due to its resilient overwintering structure , this pathogen can survive many years in soil even without host plants . In the premethyl bromide era, Verticillium wilt was a major limiting factor to strawberry production in California . Today, Verticillium wilt is one of several key soil-borne diseases facing California strawberry production and poses a long-term threat for organic strawberry production in the state.To avoid Verticillium wilt and other soil-borne diseases, as well as meet the requirements of the USDA National Organic Program , organic strawberry growers must implement crop rotation. Due to its high sensitivity to the disease, several years between strawberry plantings are necessary . For specialized strawberry growers in California, establishing a crop rotation system implies a major change in the design and management of the farming system. Due to the high costs of production and the high leasing fees of crop lands , specialized organic strawberry growers need to minimize the break time between strawberry crops as much as possible to stay in business. The following biological and cultural approaches to soil-borne disease management in strawberries have been tested: host resistance ; small cell transplants ; organic amendments such as compost ; high nitrogen organic fertilizers ; broccoli residues ; mustard residues , Sudan grass , and other cover crops ; microbial amendments including vesicular arbuscular mycorrhizal fungi ; plant growth promoting rhizobacteria ; crop rotations with broccoli, lettuce or Brussels sprouts ; mustard seed meal ; soil-less trough production ; and anaerobic soil disinfestation . Further, a minimum of a three-year rotation is recommended for strawberries that do not use chemical fumigants in Europe , the Northeast and Midwest United States, and in eastern Canada . However, no research has yet integrated multiple biological and cultural practices for different rotation periods of organic strawberries in California. The objective of this project was to demonstrate the effects of strawberry planting frequency in organic strawberry/vegetable rotations and combined biological and cultural practices on fruit yield and disease level. We hypothesized that the use of non-host rotation crops for Verticillium wilt plus bio-fumigation with broccoli, mustard cover crop residues, relatively resistant strawberry cultivars, and compost application would suppress disease sufficiently to grow strawberries in rotation every two or three years. To test the above hypothesis, in 2001, we initiated a fiveyear organic strawberry/vegetable rotation experiment in a commercial California field.The on-farm research site for this project was the Elkhorn Ranch in Moss Landing, Monterey County, CA, USA . The ranch is adjacent to the Elkhorn Slough National Estuarine Research Reserve, one of the state’s largest and the last remaining coastal wetlands and a habitat for hundreds of plant and animal species, including more than 135 aquatic bird species . The last conventional strawberry was grown in the 1997–1998 season and the last methyl bromide/chloropicrin fumigation was applied in the fall of 1997. Divided into three 8-ha parcels, in 1998 the land was placed into the mandatory three-year organic transition period, alternating winter cover crops with summer fallow.