Progress 10/01/19 to 09/30/20
Outputs
Target Audience:The target audience includes: 1) undergraduate students through formal classroom instruction, who were targeted to enhance their knowledge of how agrobiodiversity can support more sustainable agriculture systems, and to teach them ecological principles underpinning more sustainable systems; 2) graduate students and postdoctoral scholars through mentoring, who were targeted to enhance their capacity for independent research related to agrobiodiversity and soil-based ecosystem services; 3) California vegetable growers and California extension personnel (from University of California Cooperative Extension, Resource Conservation Districts, and Natural Resources Conservation Service) through workshops, webinars and presentations, who were targeted to share results from research activities; 4) Other researchers in the fields of agroecology, soil biogeochemistry, soil science, agronomy, and ecology through conference presentations and publications, who were targeted to share research results; 5) NGOs working on climate change and agriculture and soil health. Changes/Problems:The COVID pandemic presented major challenges to conducting field research, interviews with growers, and laboratory analyses. While no major changes resulted, the work has taken considerably longer than it otherwise would have. What opportunities for training and professional development has the project provided?The project has provided numerous training opportunities and professional development for undergraduate, graduate, and postdoctoral scholars. Six PhD students, three postdocs, and 12 undergraduates have received training in laboratory and field methods in agroecology, soil biogeochemistry, and soil ecology. Several PhD students have presented work at national or international conferences, which provides training in public speaking and professional development through networking. The two postdocs gained valuable experience mentoring graduate students and undergraduate students. Two undergraduate students competed senior honors theses, which provided foundational experiences in designing, conducting and analyzing research and in science writing and presentation skills. How have the results been disseminated to communities of interest?Results have been shared with communities of interest through formal classroom instruction, scientific conferences, and workshops and webinars for practitioners and extension personnel. PD Bowles teaches two large undergraduate courses (Agroecology - 80 students; Introduction to Environmental Science - 300 students) and incorporates relevant research results into both courses. A number of presentations at state and international conferences were given. What do you plan to do during the next reporting period to accomplish the goals?Goal 1 We plan to analyze two large datasets on soil microbial community composition to improve understanding of how planned diversification at the field scale and landscape structure improve soil biodiversity. The first dataset is from five long-term experiments on crop rotational diversity (see Accomplishments) and includes bacterial (16S) and fungal (ITS2) sequencing from bulk and rhizosphere soil. The second dataset is from 28 farm fields growing organic lettuce in California's central coast that vary in "diversification practices" and the surrounding landscape, and also include both bacterial and fungal sequences. Goal 2 From the same 28 fields on which we have data on microbial community composition (See Goal 1), we are also in the process of measuring four key ecosystem services - soil carbon sequestration, soil nitrogen supply and retention, soil suppression of foodborne human pathogens and water provisioning. We plan to finish analyzing laboratory samples and conduct statistical analyses to understand linkages between multiple ecosystem services and soil microbial communities and agricultural management. Goal 3 We will continue research into how AMF inoculation affects tomato responses to deficit irrigation and dry farming, and how tomato responses to AMF vary depending on soil nutrient levels and the resident AMF community. Goal 4 We plan to complete analysis of a California statewide survey of technical assistant providers on the factors influences growers to adopt or not adopt soil health practices, and to publish and share results of in depth semi-structured interviews with California organic vegetable farmers on the same topic.
Impacts
What was accomplished under these goals?
The main impact of the research and outreach conducted over the project period (see specific goals below) is increased capacity for individual growers, environmental regulators, and NGO personnel to make decisions and design policies that increase the potential for agroecological approaches to soil management that generate multiple benefits while adapting to climate change challenges. For instance, during the prior reporting period PD Bowles showed that crop rotational diversity reduces the negative impacts of drought on corn yields. This information was used during the reporting period in collaboration with a soil health-focused NGO to promote policies for crop insurance and lending that incentivize management that mitigates risk. In another example, knowledge generated on key barriers to adoption of soil health building-practices in cool season vegetable systems in California's central coasts led to conversations with regional regulators of water quality and cooperative extension personnel, ultimately resulting in some support for cover-cropping and compost applications to be included in a new proposed regulatory approach for improving water quality. Below we summarize new research accomplishments under each goal. Goal 1 Agricultural systems that increase reliance on belowground interactions for nutrient uptake can decrease reliance on fertilizers that are costly and cause environmental degradation. Arbuscular mycorrhizal fungi (AMF) are a key group of soil microbes that associate with plant roots and trade nutrients for carbon (energy) from the roots. Yet many agricultural practices are detrimental to AMF. Agricultural management systems with greater plant diversity may increase the diversity and community composition of AMF in ways that could increase resource use efficiency and/or responses to stress. Led by PhD candidate Aidee Guzman, we examined how increasing greater crop diversity affected AMF across farms in an intensive agricultural landscape, defined by high nutrient input, low crop diversity, and high tillage frequency. We assessed AMF communities across 31 field sites that were either monocultures or polycultures (growing >20 different crop types) in three ways: (1) richness, (2) diversity, and (3) composition. We also determined root colonization across these sites. We found polycultures drive the available AMF community into richer and more diverse communities while soil properties structure AMF community composition. AMF root colonization did not vary by farm management (monocultures versus polycultures), but did vary by crop host. We demonstrate that crop diversity enriches AMF communities, counteracting the negative effects of agricultural intensification on AMF, providing the potential to increase agroecosystem functioning and sustainability. Goal 2 Despite their centuries of use in agriculture and scientific evidence of crop rotation's benefits, little is known about the mechanisms by which crop rotations affect soil organic matter (SOM) dynamics through plant-soil interactions and microbial feedbacks. We tested the effect of crop rotational diversity on SOM chemistry, potential extracellular enzyme activities, and microbial community composition across five long-term experiments, each composed of contrasting intensive corn-based cropping systems, ranging from monocultures to complex five-crop rotations in the Central U.S. and Canada. At each site, we sampled three corn-based crop rotations (low, mid and high crop rotational diversity). We selected rainfed cropping systems using no-till practices and synthetic N fertilizer to isolate the effect of crop rotation history to the extent possible. Agroecosystems with the same crop rotational diversity shared similarities in molecular SOM patterns with a strong microbial signature, pointing to common transformation processes. Differences in SOM chemistry between rotations were mainly characterized by shifts in microbial necromass markers and in lipids produced or transformed by microbes rather than by intact plant lipids. The mechanisms of microbial decomposition of organic matter differed between systems, with lower resource investment into recalcitrant C-degrading enzymes with increasing crop diversity. Our results suggest that this is regulated via relative changes in microbial functional groups - emergence of relatively more non-oxidase producing microorganisms, such as arbuscular mycorrhizal fungi, rather than an absolute decrease in oxidase producing microbes. These uniform responses to increased crop rotational diversity over a wide geographical area point to altered stabilization of microbial-derived SOM and functional shifts in the microbial community as one of the main mechanisms underlying the positive plant-soil feedback in cropping systems. Goal 3 While irrigated cropping systems may not be as vulnerable to short term droughts as rainfed systems, multi-year droughts that reduce the availability of water in reservoirs or in groundwater (i.e. blue water) can result in reduced water for irrigation. In these circumstances, annual crop growers can plant the same crops on fewer acres, transition to less water intensive crops, or grow on the same acreage while using deficit irrigation. In a project led by postdoc Janina Dierks and PhD candidate Yvonne Socolar, we examined how a commercial AMF inoculant affected production of fresh market and Roma-type tomatoes under full and deficit irrigation. We found that AMF inoculation did not affect fresh market tomato yields but increased processing tomato yields by 10% in the deficit irrigation treatment, and actually decreased processing tomato yields by 18% in a full irrigation treatment. This suggests that while inoculation may be one strategy growers could use to increase yields when water availability is limited, more research is needed to understand when, where, and under what circumstances inoculation will not lead to tradeoffs for yields. Goal 4 We do not have anything new to report under this goal for the reporting period.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Bowles, T. M., Mooshammer, M., Socolar, Y., Calder�n, F., Cavigelli, M.A., Culman, S.W., Deen, W., Drury, C.F., Garcia y Garcia, A., Gaudin, A., Harkom, W.S., Lehman, R.M., Osborne, S.L., Robertson, G.P., Salerno, J., Schmer, M.R., Strock, J., and Grandy, A.S. Long-term evidence shows crop rotation diversification increases agricultural resilience to adverse growing conditions in North America. One Earth 2: 1-10
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Wade, J., Maltais-Landry, G., Lucas, D. E., Bongiorno, G., Bowles, T. M., Calder�n, F. J., et al. (2020). Assessing the sensitivity and repeatability of permanganate oxidizable carbon as a soil health metric: An interlab comparison across soils. Geoderma 366, 114235.
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Schnecker, J., Bowles, T.M., Hobbie, E., Smith, R.G., Grandy, A.S. Carbon concentration controls decomposition and microbial strategies in a model soil system. Biogeochemistry 144: 47-59.
- Type:
Book Chapters
Status:
Published
Year Published:
2020
Citation:
Rainey, C., Egerer, M., Herrmann, D., Bowles, T.M. Restoring soil and supporting food sovereignty in an urbanizing world: An interdisciplinary perspective. In: Urban Agroecology Interdisciplinary Research and Future Directions. Eds Egerer, M., Cohen, H. CRC Press.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Bowles, T.M., Carlisle, L., Ory, J., Iles, A. Perceptions of cover cropping challenges and opportunities in California's complex socioeconomic and climate environment. California Plant-Soil Conference, Fresno, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Bowles, T.M., Mooshammer, M., and Socolar, Y. Diversifying cropping systems to enhance soil microbial processes that build soil carbon and crop resilience. Soil Science Society of America Conference, San Antonio, TX
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Progress 10/01/18 to 09/30/19
Outputs
Target Audience:The target audience includes: 1) undergraduate students through formal classroom instruction, who were targeted to enhance their knowledge of how agrobiodiversity can support more sustainable agriculture systems, and to teach them ecological principles underpinning more sustainable systems; 2) graduate students through mentoring, who were targeted to enhance their capacity for independent research related to agrobiodiversity and soil-based ecosystem services; 3) California growers (vegetables, nuts)and Californiaextension personnel (from University of California Cooperative Extension, Resource Conservation Districts, and Natural Resources Conservation Service)through workshops, webinars and presentations, who were targeted to share results from research activities; 4) Other researchers in the fields of agroecology, soilbiogeochemistry, soil science, agronomy,and ecologythrough conference presentations and publications, who were targeted to share research results. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project has provided numerous training opportunities and professional development for undergraduate, graduate, and postdoctoral scholars. Six PhD students, two postdocs, and ten undergraduates have received training in laboratory and field methods in agroecology, soil biogeochemistry, and soil ecology. SeveralPhD students and two postdocs have presented work atnational or international conferences, which provides training in public speaking and professional development through networking. The two postdocs gained valuable experience mentoring graduate students and undergraduate students. Two undergraduate students competed senior honors theses, which provided foundational experiences in designing, conducting and analyzing research and in science writing and presentation skills. How have the results been disseminated to communities of interest?Results have been shared with communities of interest through formal classroom instruction, scientific conferences, and workshops and webinars for practitioners and extension personnel. PI Bowles teaches two large undergraduate courses (Agroecology - 80 students;Introduction to Environmental Science - 250 students) and incorporates relevant research results into both courses. A number of presentations at state and international conferences were given. A webinar given by PI Bowles for the NRCSon soil health has been viewed 415 times since summer 2019. What do you plan to do during the next reporting period to accomplish the goals?Goal 1 We will look at the effects of arbuscular mycorrhizal fungi on tomatoes under drought stress in Yolo County, California. We will examine how fungal inoculants and compost- by way of AMF associations -affect tomato productivity under drought and fully watered conditions. We hope to also include management practices (e.g. cover cropping or crop rotation) in the analysis, asking whether these management techniques can have comparable impacts to those that are already being tested. Goal 2 For our ongoing investigation of organic lettuce in the central coast of California, over the next year, we will be collecting our field data on soils, and beginning analyses of how different farm management practices impact soil microbial communities, and other important soil functions. These measures are important particularly in light of their role in maintaining productive and sustainable farms. With this data, we also hope to begin modeling some of these key ecosystem processes to better understand how management may impact critical ecosystem services. Goal 3 We will continue to analyze soil samples collected from five long-term experiments on crop rotational diversity, analyze data, and prepare publications. Goal 4 We will focus on qualitative and quantitative analysis of survey and inteview data, with the goal of preparing two publications during the next reporting period.
Impacts
What was accomplished under these goals?
Goal 1 Agricultural systems that increase reliance on belowground interactions for nutrient uptake can decrease reliance on fertilizers that are costly and cause environmental degradation. Arbuscular mycorrhizal fungi (AMF) are a key group of soil microbes that associate with plant roots and trade nutrients for carbon (energy) from the roots. Yet many agriculitural practices are detrimental to AMF.Agricultural management systems with increased periods of roots being present in soil, e.g. through cover cropping, have been shown to promote the abundance and diversity of AMF. Moreover, cropping systems with reduced inputs of synthetic fertilizers and pesticides can exert positive effects on AMF communities. We testedthe contribution of differently abundant and diverse AMF communities, as shaped by long-term agricultural management to crop yield, plant nutrition and nutrient cycling in tomato cropping systems.Tomato yield was lowest in the organic (OMT) system and highest in the Alfalfa -Corn -Tomato rotation (ACT). Muting the AM fungal symbiosis reduced tomato yields in all systems, except for OMT. The biggest effect of AMF on tomato yield was observed in the ACT-system, wherereduced mycorrhizal-plants had 33% lower tomato fresh yield than wildtype tomatoes.Muting AMF functioning caused yield reductions in allbut one system investigated. These results show that AM fungal communities significantly support tomato yields. However, long-term agricultural management affects the ability of AMF to provide benefits. Further analyses will revealwhether differences in AM community composition and/or AMF abundance are responsible for the observed effects and which particular management characteristics are likely to cause the observed differences in AM fungal functioning. For instance, in the ORG system, build up of soil phosphorus may have impaired AMF functioning.The findings imply that crop yields, nutrient use efficiency and overall sustainability of tomato systems can be enhanced by management practices that support AM fungal communities. Goal 2 Microbial carbon use efficiency (CUE) reflects the partitioning of organic carbon (C) taken up between respiration and growth, with the latter having the potential to be stabilized in soils, and thus plays a fundamental role in soil C sequestration and soil health. Several agricultural management practices, including crop rotation, have been shown to have the potential to increase soil C storage, but the underlying mechanisms are yet to be understood. Crop rotations are characterized by greater diversity of plant litter inputs and often higher litter quality, and have been shown to sustain soil quality and productivity by enhancing soil C, nitrogen, and microbial biomass. We assessed how crop rotational diversity affects soil microbial physiological parameters across five long-term experiments in the Central U.S. and Canada along a soil-climate gradient. Specifically, we analysed microbial CUE, growth and organic C uptake in maize-based crop rotations ranging from monocultures to five crops in rotation. To determine microbial CUE, we used a substrate-independent method that quantitatively traces18O from water into microbial DNA. We found that microbial CUE, ranging between 0.1 and 0.4, significantly varied among sites, whereas organic C uptake rates of the microbial communities were similar across the five sites, despite different organic C availabilities. These results indicate that the rate of microbial biomass production was driven by how organic C taken up was partitioned between anabolic and catabolic processes and not by the soil organic matter decomposition flux. Microbial growth rates increased with increasing crop rotational diversity. However, microbial biomass turnover was not affected because higher growth rates were accompanied by higher microbial biomass carbon pools. Microbial CUE, in turn, did not show a clear response pattern to crop rotational diversity; Compared to simple rotations, CUE increased in the mid-diverse crop rotations but not in the most diverse rotations. At the field scale, CUE may be controlled by changes in soil properties and microbial community structure induced by the type and sequence of crops included in the rotation. Therefore, we will further explore environmental and microbial community controls on microbial CUE and growth at both the regional and field scale. Goal 3 A grand challenge facing humanity is how to produce food for a growing population in the face of a changing climate and environmental degradation.Though empirical evidence remains sparse, management strategies that increase environmental sustainability, like increasing agroecosystem diversity through crop rotations, may also increase resilience to weather extremes without sacrificing yields.We used multilevel regression analyses of long-term crop yield datasets across a continental precipitation gradient to assess how temporal crop diversification affects maize yields in intensively-managed grain systems. More diverse rotations increased maize yields over time and across all growing conditions (28.1% on average), including in favorable conditions (22.6%). Notably, more diverse rotations also showed positive effects on yield under unfavorable conditions, with yield losses reduced by 14.0 to 89.9% in drought years. Systems approaches to environmental sustainability and yield resilience like crop rotation diversification are a central component of risk reduction strategies and should inform enabling policies. Goal 4 Statistics from the 2017 Census of Agriculture on cover cropping in California are grim, yet also show some optimistic signs. With 4.8% of "available" cropland planted to cover crops, California ties for 33rdplace among the 50 states. In addition, California has one of the lowest increases in cover crop acreage between 2012 and 2017, at 2.9%. Given the potential for cover crops to play a strong role in building soil health, reducing environmental impacts of agriculture, and helping farms adapt to climate change, why has progress on increasing cover cropping acreage been so limited? But at the same time, California ranks in the top ten states for number of operations reporting cover crop use, with a 26.5% increase in operations using cover crops over the same time period. To shed light on these trends, we examined the factors that influence adoption, no adoption, and abandonment of cover crops and other practices through a survey and interviews with growers and technical assistance providers. In 2018, we conducted a statewide survey of UCCE, RCD, and NRCS personnel, asking questions regarding which "soil health" building practices (including cover crops) are most commonly recommended, which federal and state policies discourage or encourage the adoption of particular practices, and what factors are the strongest motivators for farmers to implement such practices. We also conducted in-depth interviews with growers in two contrasting production systems, almonds and lettuce, to identify more specific factors and hear growers' experiences and stories with cover cropping. We found that cover cropping was the most widely recommended practice by technical assistance providers to build soil health, with 33% of respondents (n = 143 with a 36% response rate) saying they always recommend cover cropping. Barriers cited by almond and lettuce growers had differing proportions of technical vs structural factors (e.g. markets, supply chain requirements, regulatory and incentive policies). Almond growers identified several main barriers, including water availability and water competition with trees, increased risk of frost damage, and challenges with harvest. For lettuce growers, the main barriers included the cost of land, tight production schedules, and perceived conflicts with food safety policies.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Bowles, T.M. Crop rotational diversity improves maize yields and resilience in intensive cropping systems. Ecological Society of America Conference, Louisville, KY.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Bowles, T.M. Arbuscular mycorrhizas and nitrogen acquisition and cycling in agroecosystems. Soil Science Society of America Conference, San Diego, CA
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Bowles, T.M. Soil health for productive and sustainable agriculture: Evidence and Barriers. NRCS Conservation Webinar series. Online.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Yvonne Socolar, Benjamin R Goldstein, Perry de Valpine, and Timothy M Bowles. Tradeoffs between soil quality and soil health: A novel high-resolution spatial analysis of crop temporal diversity and its landscape determinants in the central U.S.. Presented at the Soil Health Institute Annual Meeting (July 2019)
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Yvonne Socolar, Benjamin R Goldstein, Perry de Valpine, and Timothy M Bowles. Crop temporal diversity is negatively associated with inherent soil quality across the Central U.S.: A novel high-resolution spatial analysis. Presented at Ecological Society of America conference (August 2019)
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Mooshammer M., S. Grandy, K. Geyer, F. Calder�n, S. Culman, B. Deen, K. Dunfield, S. Frey, V. L. Jin, M. Lehman, S. Osborne, M. Schmer, T. Bowles. Response of microbial carbon use efficiency and biomass turnover to crop rotational diversity. April 7-12, 2019, EGU General Assembly 2019, Vienna, Austria.
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Jackson, L.E., Bowles, T.M., Ferris, H., Margenot, A., Hollander, A., Garcia-Palacios, P., Duafresne, T., S�nchez-Moreno, S. Plant and soil biodiversity across the borders between arable and forest ecosystems in a Mediterranean landscape. Applied Soil Ecology 136: 122-138
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Mooshammer M., S. Grandy, K. Geyer, F. Calder�n, S. Culman, B. Deen, K. Dunfield, S. Frey, V. L. Jin, M. Lehman, S. Osborne, M. Schmer, T. Bowles. Response of microbial growth and carbon use efficiency to crop rotational diversity across a soil-climate gradient. August 11-16, 2019. ESA & USSEE 2019 Joint Meeting.
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