Papers by Kerri Steenwerth
Science of The Total Environment
This report describes the potential vulnerability of specialty crops, field crops, forests, and a... more This report describes the potential vulnerability of specialty crops, field crops, forests, and animal agriculture to climate-driven environmental changes. Here, vulnerability is defined as a function of exposure to climate change effects, sensitivity to these effects, and adaptive capacity. The exposure of specific sectors of the agricultural and forestry industries varies across the region because the Southwest is climatically and topographically diverse. There is also variability in the sensitivity of different systems to the effects of climate change. Most significantly, there is potential within agricultural and forestry systems to adjust to climate-related effects either through inherent resilience or through conservative management practices. The purpose of this analysis is to describe regional vulnerabilities to climate change and adaptive actions that can be employed to maintain productivity of working lands in the coming decades.
Climatic Change
Increased temperatures in the Southwestern USA will impact future crop production via multiple pa... more Increased temperatures in the Southwestern USA will impact future crop production via multiple pathways. We used four methods to provide an illustrative analysis of midcentury temperature impacts to eight field crops. By midcentury, cropland area thermally suitable for maize cultivation is projected to decrease, while area suitable for cotton cultivation expands Climatic Change (2018) 148:403-417 https://doi.northward and nearly doubles in extent. The increase in area exposed to daily temperatures > 35°C was highest for oat and maize. Estimates of yield reduction from heat stress for both maize and cotton indicate that historically, SW heat stress reduced cotton yield by 26% and maize yield by 18% compared to potential yield. By midcentury, we predict yield reduction from heat stress will reduce cotton and maize yields by 37 and 27%, respectively, compared to potential yield. Our results contradict the notion that the warmest counties cultivating field crops will be the most impacted. Rather, future temperature, total crop area and crop sensitivity contribute to more complex county-level impacts. Identification of representative target environments under future temperature regimes can inform development of farm-based networks to evaluate new crop germplasm with increased heat tolerance and viable adaptation and management strategies to respond effectively to future temperatures.
Agricultural Water Management
Climatic Change
Increasing global temperatures are likely to have major impacts on agriculture, but the effects w... more Increasing global temperatures are likely to have major impacts on agriculture, but the effects will vary by crop and location. This paper describes the temperature sensitivity and exposure of selected specialty crops in California. We used literature synthesis to create several sensitivity indices (from 1 to 4) to changes in winter minimum and summer maximum temperature for the top 14 specialty crops. To estimate exposure, we used seasonal period change analysis of mid-century minimum and maximum temperature changes downscaled to county level from CMIP5 models. We described crop vulnerability on a county basis as (crop sensitivity index × county climate exposure × area of crop in county); individual crop vulnerabilities were combined to create an aggregate index of specialty crop vulnerability by county. We also conducted analyses scaled by crop value rather than area, and normalized to Climatic Change total specialty crop area in each county. Our analyses yielded a spatial assessment highlighting seasons and counties of highest vulnerability. Winter and summer vulnerability are correlated, but not highly so. High-producing counties (e.g., Fresno County in the San Joaquin Valley) are the most vulnerable in absolute terms, while northern Sacramento Valley counties are the most vulnerable in relative terms, due to their reliance on heat-sensitive perennial crops. Our results illustrate the importance of examining crop vulnerability from different angles. More physiological and economic research is needed to build a comprehensive picture of specialty crop vulnerability to climate change.
Soil Biology and Biochemistry, 2016
Little is known about the hierarchical effects of management practices, soil attributes and locat... more Little is known about the hierarchical effects of management practices, soil attributes and location factors on structure of vineyard soil microbiota. A hierarchical effect occurs when the specific influence of an experimental factor (e.g. cover crop type, compost application) on soil-borne bacterial communities is greater within a subset composing the larger set but not across the entire set (e.g. bacterial communities only respond to a management practice within a subset of soil types but not across the entire set composed of all soil types). To address this concept, we measured differences in soil bacterial and archaeal diversity in wine-grape vineyard soils throughout Napa Valley, California. We describe how vineyard management practices influence soil resources, which in turn determine shifts in soil-borne bacterial communities. Soil bacterial communities were structured with respect to management practices, specifically cover crop presence and cover crop mix, tillage, and agricultural system designation, i.e. conventional, organic and biodynamic production systems. Distinctions with respect to management were associated with differences in pH and soil resource pools: total carbon and total nitrogen of the <53 and 53e250 mm particulate organic matter fractions, and potentially mineralizable nitrogen. Findings in this study suggest management practices in vineyard production systems directly influence soil microbial community structure, as mediated by shifts in soil resource pools. However, hierarchical effects occur, in which b-diversity is more strongly affected by specific management practices only within certain soil types, tillage or no-till soils or winegrowing region. This work allows for subsequent assessments of interrelationships of vineyard management, microbial biodiversity and their combined influence on soil quality, vine health, and berry quality.
Weed Science, 2007
Vineyard weed communities were examined under the influence of an organic weed control practice, ... more Vineyard weed communities were examined under the influence of an organic weed control practice, soil cultivation with a Clemens cultivator, and applications of the herbicide glyphosate. Experimental treatments (winter-spring glyphosate, spring cultivation, fall-spring cultivation, fall cultivation-spring glyphosate) were carried out in a California wine grape vineyard for 3 yr. Cultivation alone was not as effective as glyphosate, based on lower weed biomass in the glyphosate-only treatment in 2 of 3 yr. However, given that two passes with the Clemens cultivator decreased weed biomass relative to one pass, it is possible that additional passes could bring about further reductions. Pairing fall cultivation with glyphosate was as effective at reducing weed biomass as two glyphosate applications in 2 of 3 years, suggesting that substituting a glyphosate application with cultivation may be an effective method of reducing herbicide use in vineyards. Canonical correspondence analysis revealed significant treatment effects on community structure. Weed composition in the spring cultivation treatment was significantly different from that of all other treatments. Based on our findings of high relative abundance of field bindweed and sowthistle species, which are problematic vineyard weeds that grow into the vine canopy and disrupt canopy management practices, it is possible that either the presence of soil disturbance or the absence of herbicides favored these species. Nomenclature: Glyphosate; annual sowthistle, Sonchus oleraceus L. SONAL; field bindweed, Convolvulus arvensis L. CONAR; spiny sowthistle, Sonchus asper (L.) Hill SONAS; wine grape, Vitis vinifera L. 'Merlot'.
PLOS ONE, 2015
How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a... more How farming systems supply sufficient nitrogen (N) for high yields but with reduced N losses is a central challenge for reducing the tradeoffs often associated with N cycling in agriculture. Variability in soil organic matter and management of organic farms across an agricultural landscape may yield insights for improving N cycling and for evaluating novel indicators of N availability. We assessed yields, plant-soil N cycling, and root expression of N metabolism genes across a representative set of organic fields growing Roma-type tomatoes (Solanum lycopersicum L.) in an intensively-managed agricultural landscape in California, USA. The fields spanned a three-fold range of soil carbon (C) and N but had similar soil types, texture, and pH. Organic tomato yields ranged from 22.9 to 120.1 Mg ha -1 with a mean similar to the county average (86.1 Mg ha -1 ), which included mostly conventionallygrown tomatoes. Substantial variability in soil inorganic N concentrations, tomato N, and root gene expression indicated a range of possible tradeoffs between yields and potential for N losses across the fields. Fields showing evidence of tightly-coupled plant-soil N cycling, a desirable scenario in which high crop yields are supported by adequate N availability but low potential for N loss, had the highest total and labile soil C and N and received organic matter inputs with a range of N availability. In these fields, elevated expression of a key gene involved in root N assimilation, cytosolic glutamine synthetase GS1, confirmed that plant N assimilation was high even when inorganic N pools were low. Thus tightlycoupled N cycling occurred on several working organic farms. Novel combinations of N cycling indicators (i.e. inorganic N along with soil microbial activity and root gene expression for N assimilation) would support adaptive management for improved N cycling on organic as well as conventional farms, especially when plant-soil N cycling is rapid.
Although not yet regulated in AB 32 Global Warming Solutions Act, the greenhouse gas nitrous oxid... more Although not yet regulated in AB 32 Global Warming Solutions Act, the greenhouse gas nitrous oxide (N2O) is a major concern for Californias agricultural industry. Since March 2011, we have evaluated carbon dioxide (CO2) and N2O emissions from vineyards across three soil types of different geologic history and under varying conventional management systems in the Lodi Wine-grape District in the Central Valley of California. Soils of the District vary in space as a result of the depositional history of the parent materials and subsequent weathering. We sampled the following soils from this soil sequence: 1) Slightly weathered granitic alluvium with low clay content located on the southern side of the district; 2) Intermediately weathered soils derived from granitic alluvium with high clay content located on the northern side of the district; and, 3) Highly weathered soils derived from metavolcanic and metasedimentary alluvium with intermediate clay content and rocky soils located on th...
The International Journal of Life Cycle Assessment, 2015
ACS Symposium Series, 2011
ABSTRACT
Weed Science, 2007
Vineyard weed communities were examined under the influence of an organic weed control practice, ... more Vineyard weed communities were examined under the influence of an organic weed control practice, soil cultivation with a Clemens cultivator, and applications of the herbicide glyphosate. Experimental treatments (winter–spring glyphosate, spring cultivation, fall–spring cultivation, fall cultivation–spring glyphosate) were carried out in a California wine grape vineyard for 3 yr. Cultivation alone was not as effective as glyphosate, based on lower weed biomass in the glyphosate-only treatment in 2 of 3 yr. However, given that two passes with the Clemens cultivator decreased weed biomass relative to one pass, it is possible that additional passes could bring about further reductions. Pairing fall cultivation with glyphosate was as effective at reducing weed biomass as two glyphosate applications in 2 of 3 years, suggesting that substituting a glyphosate application with cultivation may be an effective method of reducing herbicide use in vineyards. Canonical correspondence analysis rev...
Weed Science, 2008
Vineyard weed communities were examined under four dormant-season cover-crop systems representati... more Vineyard weed communities were examined under four dormant-season cover-crop systems representative of those used in the north-coastal grape-growing region of California: no-till annuals (ANoT) (rose clover, soft brome, zorro fescue), no-till perennials (PNoT) (blue wildrye, California brome, meadow barley, red fescue, yarrow), tilled annual (AT) (triticale), and a no-cover-crop tilled control (NoCT). Treatments were carried out for 3 yr in the interrows of a wine grape vineyard. Glyphosate was used to control weeds directly beneath the vines, in the intrarows. Treatments significantly impacted weed biomass, community structure, and species diversity in the interrows. Orthogonal contrasts showed that tillage, and not the presence of a cover crop, impacted interrow weed biomass. Distance-based redundancy analyses (db-RDA) revealed significant effects of the cover-crop systems and of tillage on weed community structure in the interrows. For scarlet pimpernel and spiny sowthistle, the ...
ABSTRACT Greenhouse gas emissions from agricultural soils can differ greatly across the landscape... more ABSTRACT Greenhouse gas emissions from agricultural soils can differ greatly across the landscape depending on soil type, landscape formation and management, making the implementation of mitigation practices challenging. In our study, we evaluated the carbon dioxide and nitrous oxide emissions from vineyard soils across a broad landscape in the Lodi Wine-grape District representing three soil types of different geologic history and under varying conventional management systems in the Central Valley of California. Soils of the District vary in space as a result of the depositional history of the parent materials from which the soils formed and subsequent weathering. The nature of the deposition of these materials has resulted in systematic patterns of soils in space. We sampled the following soils from this soil sequence over the larger landscape: 1) Slightly weathered granitic alluvium with low clay content located on the southern side of the district; 2) Intermediately weathered soils derived from granitic alluvium with high clay content located on the northern side of the district; and, 3) Highly weathered soils derived from metavolcanic and metasedimentary alluvium with intermediate clay content and rocky soils located on the eastern side of the district. The climate is Mediterranean with cool, moist winters and hot, dry summers. Initial results indicated that under wet conditions, the soils had similar carbon dioxide emissions with little variation between management or landscape formation. However, carbon dioxide emissions were typically higher in the alley than in the vine row. Nitrous oxide emissions were more variable in the higher clay soils as compared to sandier soils (0-180 g N/ha/day and 0-20 g N/ha/day, respectively). Nitrous oxide emissions were similar from the soil in the alley and vine row. We expect to see similar variability for carbon dioxide emissions under drier conditions later in the summer, but predict that it will differ by landscape position during pulse events (i.e., precipitation, irrigation, tillage) and that the magnitude of the differences will lessen with increased soil moisture and cooler temperatures in the winter. Though management such as tilling and irrigation can cause pulses of greenhouse gases from vineyard soils, our initial findings suggest that on a landscape level over longer time periods, differences between the soils and geologic history may be a better predictor of greenhouse gas emissions than management alone.
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Papers by Kerri Steenwerth