2012 Annual Report
1a.Objectives (from AD-416):
1. Improve databases and provide other information on the soil C stocks, C-sequestration, and greenhouse gas (GHG) emission and fluxes of current and/or new soil management and cropping systems by use of measurement and/or model based approaches.
2. Develop sustainable biofuel production systems and practices that result in improved soil C sequestration, efficient use and recycling of applied nutrients (especially N), and minimal GHG emissions.
3. Characterize and measure the influences and processes of environmental and plant-related controls on C and N cycling and storage in soils.
4. Develop processes, primarily microbiological, that.
1)minimize soil-borne disease thereby maintaining soil ecosystems and crop productivity,.
2)enhance biofuel production, and.
3)remediate damaged, and protect undamaged, soil and water.
5. Develop management practices and decision support tools that improve nutrient use efficiency and reduce losses in agricultural systems.
1b.Approach (from AD-416):
This research addresses priority science questions in the strategic plan for the Climate Change, Soils and Emissions Research (NP212) and provides a scientific foundation for decision-making and policy development. The five objectives in this project integrate studies focusing on effects of management practices on soil processes and sustainable crop growth and yield. Objective 1 addresses the need for improved databases and provides other information on the soil C stocks, C-sequestration, and GHG emission and fluxes of current and new soil management and cropping systems. These data bases will be used to improve models and decision support systems. Objective 2 studies address sustainable biofuel and irrigated conservation tillage production systems and practices to improve soil C sequestration, efficient use and recycling of applied nutrients (especially N), and minimize GHG emissions. Objective 3 studies focus on characterizing and measuring the influences and processes of environmental and plant-related controls on C and N cycling, pool dynamics, and storage in soils. Objective 4 examines soil productivity and remediation tools that reduce soil-borne diseases and protect soils and soil waters from damage from soil contaminants. The goal is to utilize microbial isolates and communities for bioenergy production, biocontrol of soil-borne pathogens, and to remediate damaged soils. Objective 5 studies focus on improving nutrient use efficiency, especially N, and developing more advanced decision support tools (e.g., indices and models) for improved nutrient management. The overall SPNR research focus is on biological processes and management practices that influence SOC, GHG emissions, microbial and rhizosphere biology, pesticide/nutrient/contaminant removal from soil, bioenergy production, and nutrient use efficiency. All of these research projects share the common goal of improving or maintaining farm profitability while practicing sustainable and environmentally friendly agriculture.
Objective 1: Improved relational databases are needed to assess land uses to reduce greenhouse gas (GHG) emissions. A general template allows comprehensive data entry from ARS GRACEnet and REAP locations, is adaptable for use by other ARS programs, and by other countries. Used with ‘process-based’ models, national inventories can be improved. Model testing and development continues to meet national needs such as input into national inventories of US greenhouse gas emissions and sinks.
Objective 2. Sustainable biofuel production systems continue to be investigated in relation to soil C sequestration. Research establishes that in the Western Cornbelt, over half of the C was sequestered below 30cm depth under dryland switchgrass and corn. Effect of tillage on grain yields and greenhouse gas (GHG) emissions are being investigated, as are GHG contributions of urban turfgrass systems that may improve C sequestration, and minimize GHG emissions. Plant biochemical markers and fragments in soil help understand linkages to production and post-production conditions for biochar on sorbed volatile organic compounds. Nearly 2000 bacterial isolates obtained from tropical rainforest sources continue to be screened for novel biochemical properties. Two isolates are being characterized for their ability to degrade lignin.
Objective 3. A CAST report and an Elsevier book, both on GHG and Global Change were published. In VA, most of the SOC across 48 farmer fields was mineral associated, and additional C storage was in aggregate and labile pools susceptible to management. Techniques including determination of particulate and mineral associated organic C, isotopic, and others allow soil characterization for influences and processes of environmental and plant-related controls on C and N cycling and storage in soils. Effects of temperature and moisture were used to estimate potential C and N losses that might result from global climate change across the US Great Plains during the next 30yr.
Objective 4. Shallow vadose zone remediation for soil and water degradation, enhancing residue decomposition for biofuels, and maintaining soil productivity include a pilot scale biobarrier designed to intercept runoff from cattle pens, to determine nitrate removal. Additional studies use aerobic and anaerobic biobarriers to remediate groundwater contaminated with hexazinone. A similar study was initiated with imidacloprid, a neonicotinoid insecticide. A study to investigate selenium movement through deep soils was completed and the results published. Twenty bacterial isolates with bioactivity against Phytophthora spp. have been identified and further assayed for siderophore production.
Objective 5. Decision support tools to improve nutrient use efficiency and reduce losses in agricultural systems now include a Nitrogen Index app. The Smartphone app can be run at a given farm and results emailed to help users assess and improve N use efficiency. A report was published on the science of climate change and conservation practices entitled "Nitrogen in Agricultural Systems: Implications for Conservation Policy".
Model Testing and National Scale Simulations Performed: National scale, models are used to estimate emissions for the agricultural sector reported in the US greenhouse gas (GHG) inventory. ARS researchers at Fort Collins, CO, in collaboration with scientists from Colorado State University, tested the DayCent ecosystem model and then ran the model for over 300,000 locations across the US representing the vast majority of agricultural land in the USA. Model outputs for soil GHG fluxes were aggregated to the state and national levels and reported in the Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2010 (published by the EPA).
GRACEnet Data Used to Evaluate Greenhouse Gas (GHG) Flux Estimates: Most national inventories use IPCC Tier 1 methodology (a simple spreadsheet approach)to estimate agricultural GHG fluxes reported to the United Nations Framework Convention on Climate Change (UNFCCC). Process based models are potentially more accurate, but these must be tested using field observations. Fluxes of GHG using the DayCent ecosystem model and IPCC Tier 1 methodology were tested by ARS Scientists at Fort Collins across 8 GRACEnet and 7 other field sites. The DAYCENT estimates were less biased, showed a stronger correlation with measured values, and have less uncertainty than does the Tier 1 methodology.
Sequestration of Carbon under dryland Switchgrass. During a 9 yr C sequestration study near Lincoln, NE, ARS Scientists at Fort Collins in collaboration with other ARS Scientists, switchgrass and corn grown with best management had annual SOC increases exceeding 2 Mg C/ha/yr in the 0 to 150 cm depth. The project was conducted under two different projects for both crops, over 50% of the increase was below 30 cm. SOC sequestration by switchgrass was 2 to 4 times greater than used in models that also assume no SOC sequestration by corn. The results indicate that N rates and harvest management regimes can affect SOC sequestration. Use of uniform soil C effects for bioenergy crops from sampling depths of 30 to 40 cm across agro-ecoregions for large scale LCA is questionable.
Volatile organic compounds in biochar. Addition of biochar to soil is believed to increase soil carbon sequestration. ARS Scientists at Fort Collins in collaboration with Colorado State University have recognized that limited data exist on the chemistry of sorbed volatile organic compounds (VOCs) of biochars. Feedstocks, pyrolysis technology, and pyrolysis temperatures effects on sorbed VOCs of over 70 biochars were studied. Sorbed VOC composition dependence on feedstock was unclear, suggesting instead linkage with feedstock production and post-production conditions and processing. Users should recognize high inconsistency and chemical dissimilarity of sorbed VOCs to help explain the response variability to biochar addition to soils and the need for VOC characterization before land application.
More information is needed on the effects of manure management on greenhouse gas (GHG) emissions from agricultural fields. New studies on Dairy Manure are initiated by ARS Scientists in Fort Collins, CO. Field and laboratory work completed and two manuscripts submitted by ARS scientist in Fort Collins, CO—one accepted, on the effects of N source on nitrous oxide emissions from a clay loam soil under irrigated, no-till continuous corn management. A manuscript on N source effects on ammonia loss is revised and resubmitted. New studies were initiated in FY12 to examine the effects of dairy manure application on nitrous oxide compared to granular urea and stabilized urea under silage corn production and another study to evaluate the effects of N source on nitrous oxide loss from a golf course environment.
Urban Turfgrass may have Important Impacts as a source of Nitrous Oxide. ARS scientist in Fort Collins, CO have observed that fertilized and irrigated turfgrass in urban areas may have important impacts on emissions of greenhouse gases (GHG) into the atmosphere and be a source of N2O emission. Data is being collected and analyzed from a Fort Collins, CO golf course. GHG were collected from fairway, rough, green and native areas. Enhanced N Fertilizers to inhibit GHG emissions were applied to the fairway and rough areas. Sites under both high and well-drained soil moisture conditions are being studied. Data collection across several golf courses includes energy and fuel uses, DAYCENT modeling and trace gas emissions.
DayCent Simulations of Biofuel Systems Validated: Biofuels may reduce greenhouse gas (GHG) emissions but rigorous life cycle GHG accounting is required to quantify this reduction. Collaboratively with other ARS and University scientists, ARS scientists at Fort Collins, CO tested the utility of the DayCent ecosystem model with biomass yields and GHG fluxes from biofuel studies in 4 states. The model was shown to accurately represent yields and emissions for corn, switchgrass, and miscanthus systems. DayCent can subsequently be applied to perform complete lifecycle analyses of GHG emissions for biofuel systems across the US at regional scales.
Biosolids and Carbon Sequestration Virginia Coastal Plains. We sampled 48 grower’s fields on 3 soil series. Soils under NT with BS had more SOC than the RT sites with no BS in 2 soils, and SOC were 3-3.4 Mg C ha-1 greater than reported before. Most SOC was mineral-associated. Few studies document the potential for the use of biosolids or their effects on C and N sequestration in producer fields. ARS scientist in Fort Collins, CO worked with the local soil conservation district and growers in the VA Coastal Plain. The growers practice rotational (RT) and continuous no-tillage (NT) and biosolid (BS) application, but few studies document the effects on C and N sequestration in producer fields. Practices with less soil disturbance and more C input are needed and future C storage will be in aggregate and labile pools that are potentially lost by changing management.
Two Major Publications dealing with Agriculture and Global Change. Two major contributions have been published to improve management and provide information to users and policy makers by ARS scientist in Fort Collins, CO and other ARS and University scientists nationally. The first is a 106 page report by the Council for Agricultural Science and Technology Report (CAST report number 142) entitled, Carbon Sequestration and Greenhouse Gas Fluxes in Agriculture: Challenges and Opportunities. In addition the 2012 Book (547 pages), entitled Managing Agricultural Greenhouse Gases: Coordinated Agricultural Research through GRACEnet to Address our Changing Climate (Elsevier Sci. Pubs.) provides perhaps the most complete evaluation of Agriculture and Global Climate Change available now and perhaps well into the future.
Potential effect of Climate Change on US Great Plains Soil C and N. Soils from across 14 sites in the US Great Plains were examined by ARS scientist in Fort Collins, CO. This study indicates that the potential effect of climate change, based on mean annual temperature (MAT) and the mean annual precipitation to potential evapotranspiration (MAP:PET) ratio are that a 1ºC increase in MAT could result in loss of 486 Tg of SOC (1.78 Pg CO2eq) and release of 180 kg SON/ha from the top 10cm of soil over 30 yr. Increased warming and land conversion from CRP to cropping may significantly decrease SOC stock. Management practices to minimize soil erosion and reduce ET may offset C and N loss.
Phytophthora is a serious fungal disease organism for many major US crops, including potato. Qualitative and quantitative changes in Phytophthora host and non-host plant gene expression were found to be significantly different. Samples were collected and analyzed for microbial diversity from a field trial of potato in the San Luis Valley. Host tannin contents and P. ramorum colonization and sporulation have been initiated. Plant material from 50 Port Orford cedar families have also been analyzed by GC-MS and P. lateralis susceptibility tests have been conducted by Oregon State University collaborators. Additional phenolic compound screens have been conducted to identify potential resistance biomarkers.
The goal of these collaborative studies is to better understand potato cultivar interactions with their soil and endophyte microbial communities. New plant material has been acquired by ARS Scientists in Fort Collins, CO. Plant and soil samples from 12 potato cultivars growing in three locations (CA, TX, CO) have been obtained from the Western Regional potato trials. Samples have been processed and submitted for analysis to determine the cultivar-specific microbial communities. The cultivars are also in the process of being analyzed by GC-MS and nutrient analysis to better understand the cultivar-microbial interaction and its influence of potato growth and nutrition.
Nearly 2000 Bacterial Isolates. ARS scientists in Fort Collins, CO have developed a collection of nearly 2000 bacterial isolates obtained from tropical rainforest soils and decaying logs. This collection continues to be screened for novel biochemical properties. Twenty isolates have been identified that have bioactivity against Phytophthora spp. and are further being assayed for siderophore production.
Lignin-degrading Bacterial Isolates. A collection of nearly 2000 bacterial isolates obtained from tropical rainforest soils and decaying logs continue to be screened for novel biochemical properties. Two novel degrading isolates are being further characterized for their associated enzymes and ability to degrade lignin.
Removal of Nitrate. Nitrate is a major agricultural groundwater contaminant in areas where cattle are raised. A field study found that biobarriers placed in shallow vadose zone soils can intercept and remove nitrate from percolating soil water providing a remediation recommendation for an important agricultural water contaminant.
Removal of Insecticide from Groundwater. A study that used aerobic and anaerobic biobarriers to remediate groundwaters contaminated with hexazinone was completed and a manuscript submitted, accepted and published. A study has been initiated with imidacloprid, a neonicotinoid insecticide. Ho 4.4c: A collaborative study investigating selenium movement through deep soils was completed and the results were published.
Corn grain yields were significantly greater with polymer-coated urea than with conventional urea. All planned field and laboratory work was completed by ARS scientists in Fort Collins, CO as scheduled. Field work on this project is completed (3 years of data collection). Data is being summarized and a manuscript is in preparation. Corn grain yields were significantly greater with polymer-coated urea than with conventional urea. Corn grain yields were not different between a stabilized urea and conventional urea
The first Nitrogen Index app was just released in 2012. Nitrogen losses from agricultural systems negatively impact ecosystems. The new smartphone app can be run at a given farm and can even email the results, helping users assess and improve nitrogen use efficiency. The Index has been downloaded hundredths of times by national and international users (http://www.ars.usda.gov/npa/spnr/nitrogentools). An invited SWCS workshop was conducted and the tool was covered in an ASA online nitrogen course.
Conservation Practices to Mitigate and Adapt to Climate Change. ARS scientists in Fort Collins, CO published a feature article on conservation practices to adapt to climate change. The Soil and Water Conservation Society, a national and international society with 5,000 members, requested a publication reviewing the science of climate change and conservation practices. This paper was used as a scientific reference by the SWCS to develop its position statement on climate change and conservation. Conservation practices are key for adaptation to climate change.
Nitrogen in Agricultural Systems: Implications for Conservation Policy. The USDA-ERS publication “Nitrogen in Agricultural Systems: Implications for Conservation Policy” was published. Only about one-third of U.S. cropland is meeting three criteria for good nitrogen management (rate, method, time). This key paper was written in cooperation with ARS and was transferred to other USDA agencies and the general public (http://www.ers.usda.gov/publications/err-economic-research-report/err127.aspx). Scientific societies have also advertised the link to the paper to thousands of members.
Relational Database Populated. Relational databases are needed so researchers can access data generated by ARS and other scientists. In collaboration with other ARS scientists a general data entry template was designed by ARS Scientists at Fort Collins, reviewed, and revised for comprehensive data from more than 35 ARS Research Units for various cropping, biofuel, and grazing studies. Data have been populated into the template and uploaded to an SQL (Structured Query Language) for managing data in a relational database. Easy access to greenhouse gas (GHG) flux, soil, vegetation, and model driver data allow meta-analyses, testing of existing GHG flux and crop growth models, and for developing new models.
Berrada, A., Halvorson, A.D. 2012. Manure and nitrogen fertilizer effects on corn productivity and soil fertility under drip and furrow irrigation. Archives of Agronomy and Soil Science . p. 1-9.
Halvorson, A.D., Del Grosso, S.J. 2011. Nitrogen source effects on nitrous oxide emissions from irrigated cropping systems in Colorado. American Chemical Society Symposium Series. American Chemical Society Symposium Series. 1072:15-27.
Paul, E., Follett, R.F., Haddix, M., Pruessner, E.G. 2011. Soil N dynamics related to soil C and microbial changes during long-term incubation. Soil Science. 176: 527-536.
Follett, R.F., Mooney, S., Morgan, J.A., Paustian, K., Allen Jr, L.H., Archibeque, S., Del Grosso, S.J., Derner, J.D., Dijkstra, F., Franzluebbers, A.J., Kurkalova, L., Mccarl, B., Ogle, S., Parton, W., Petersen, J., G. Philip, R., Schoeneberger, M., West, T., Williams, J. 2011. Carbon sequestration and greenhouse gas fluxes in agriculture: Challenges and opportunities. Council for Agricultural Science and Technology Issue Paper. 112 p.
Qian, Y., Follett, R.F. 2011. Chapter 8. Carbon dynamics and sequestration in urban turfgrass ecosystems. In: Lal, R. and Augustin, B., editors. Carbon Sequestration in Urban Ecosystems. Springer Science+Business Media B.V. 2012. DOI 10.1007/978-94-007-2366-5_8
Del Grosso, S.J., Grant, D. 2011. Reducing agricultural greenhouse gas emissions: role of biotechnology, organic systems, and consumer behavior. Carbon Management. 2(5); 505-508.
Badri, D.V., Chaparro, J.M., Manter, D.K., Martinoia, E., Vivanco, J. 2012. Influence of ATP-binding cassette transporters in root exudation of phytoalexins, signals, and disease resistance. Frontiers in Plant Science. 3(149):1-17.
Bailey, R.T., Hunter, W.J., Gates, T.K. 2012. The influence of nitrate on selenium in irrigated agricultural groundwater systems. Journal of Environmental Quality. 41:783-792.
Chaparro, J.M., Sheflin, A.M., Manter, D.K., Vivanco, J.M. 2012. Manipulating the soil microbiome to increase soil health and plant fertility. Biology and Fertility of Soils. 48:489-499.
Davis, S., Parton, W., Del Grosso, S.J., Keough, C., Marx, E., Adler, P.R., Delucia, E. 2011. Impact of second-generation biofuel agriculture on greenhouse gas emissions in the corn-growing regions of the US. Frontiers in Ecology and the Environment. 10:69-74.
Follett, R.F., Stewart, C.E., Pruessner, E.G., Kimble, J. 2012. Effects of Climate Change on soil carbon and nitrogen storage in the US Great Plains. Special Issue "Mitigation of Climate Change". Journal of Soil and Water Conservation. 12:115-125.
Halvorson, A.D., Schlegel, A.J. 2012. Crop rotation effect on soil carbon and nitrogen stocks under limited irrigation. Agronomy Journal. 104:1265-1273.
Halvorson, A.D., Jantalia, C. 2011. Nitrogen fertilization effects on irrigated no-till corn production and soil carbon and nitrogen. Agronomy Journal. 103: 1423-1431.
Halvorson, A.D., Del Grosso, S.J., Jantalia, C.P. 2011. Nitrogen source effects on soil nitrous oxide emissions from strip-till corn. Journal of Environmental Quality. 40:1775-1786.
Hunter, W.J., Shaner, D.L. 2012. Removing hexazinone from groundwater with microbial bioreactors. Current Microbiology. 64:405-411.
Hunter, W.J., Manter, D.K. 2012. Pseudomonas kuykendallii sp. nov.: A novel y-Proteobacteria isolated from a hexazinone degrading bioreactor. Current Microbiology. 65:170-175.
Santhanam, N., Badri, D., Decker, S., Manter, D.K., Reardon, K., Vivanco, J. 2012. Lignocellulose Decomposition by Microbial Secretions. In: Baluska, F. and Vivance, J.M. editors. Secretions and Exudates in Biological Systems. Springer, NY. pp. 125-153.
Sherrod, L.A., Hunter, W.J., Reeder, J., Ahuja, L.R. 2012. A rapid and cost effective method for soil carbon mineralization under static incubations. Communications in Soil Science and Plant Analysis. 43:6. 958-972. http://dx.doi.org/10.1080/00103624.2012.653031.
Spokas, K.A., Novak, J.M., Stewart, C.E., Cantrell, K.B., Uchimiya, S.M., Dusaire, M.G., Ro, K.S. 2011. Qualitative analysis of volatile organic compounds on biochar. Chemosphere. 85(5):869-882.
Stewart, C.E. 2011. Evaluation of angiosperm and fern contributions to soil organic matter using two methods of pyrolysis-gas chromatography-mass spectrometry. Plant and Soil. 351:31-46.
Stewart, C.E., Follett, R.F., Wallace, J., Pruessner, E.G. 2012. Biosolid and Tillage Effects on Physically Isolated Fractions: Implications for Conservation Management of three Virginia Coastal Plain Soil Series. Soil Science Society of America Journal. 76:1257-1267.
Sugiyama, A., Manter, D.K., Vivanco, J. 2012. Co-adaptationary Aspects of the Underground Communication Between Plants and Other Organisms. In: Witzany, G. editor. Biocommunication of Plants. G. Witzany (ed). Springer, NY. pp. 361-376.
Adler, P.R., Del Grosso, S.J., Inman, D., Jenkins, R.E., Spatari, S., Zhang, Y. 2012. Mitigation opportunities for life cycle greenhouse gas emissions during feedstock production across heterogeneous landscapes. In: Liebig, M., Franzluebbers, A.J., Follet, R.F., editors. Managing Agricultural Greenhouse Gasses: Coordinated agricultural research through GRACEnet to address our changing climate. New York, NY: Elsevier Inc. p. 203-219. DOI: 10.1016/B978-0-12-386897-8.00012-7.
Del Grosso, S.J., Parton, W.J., Keough, C., Reyes-Fox, M.A. 2011. Special features of the dayCent modeling package and additional procedures for parameterization, calibration, validation, and applications. Soil Science Society of America Special Publication Book Chapter. p. 155-176.
Del Grosso, S.J., Parton, W., Adler, P.R., Davis, S., Keogh, C., Marx, E. 2012. DayCent model simulations for estimating soil carbon dynamics and greenhouse gas fluxes from agricultural production systems. Book Chapter. New York, NY: Elsevier Inc. p. 241-250.
Halvorson, A.D., Steenwerth, K.L., Suddick, E.C., Liebig, M.A., Smith, J.L., Bronson, K.F., Collins, H.P. 2012. Management to reduce greenhouse gas emissions in western U.S. croplands. Elsevier. New York, NY: Elsevier Inc. p. 167-182.
Liebig, M.A., A.J. Franzluebbers, and R.F. Follett (Editors). 2012. Managing agricultural greenhouse gases: Coordinated agricultural research through GRACEnet to address our changing climate. San Diego, CA:Academic Press. 547 pp.
Follett, R.F. 2012. Beyond Mitigation: Adaptation of agricultural strategies to overcome projected climate change. New York, NY: Elsevier Inc. p. 693-718.
Vogel, K.P., Follett, R.F., Varvel, G.E., Mitchell, R., Kimble, J. 2012. Soil carbon sequestration by switchgrass and no-till maize grown for bioenergy. BioEnergy Research. DOI 10.1007/s12155-012-9198-y.
Follett, R.F., Liebig, M.A., Franzluebbers, A.J. 2012. Preface to book entitled: Managing Agricultural Greenhouse Gases: Coordinated Agricultural Research through GRACEnet to Address our Changing Climate. New York, NY: E;sevier Inc. p. xi - xiii.
Figueroa-Viramontes1, U., Delgado, J.A., Cueto-Wong, J., Núñez-Hernández, G., Reta-Sanchez1, D., Barbarick, K. 2011. A new nitrogen index to elvaluate nitrogen losses in intensive forage systems in Mexico. Agriculture, Ecosystems and Environment. 142:352-364.
Ribaudo, M., Delgado, J.A., Hansen, L., Livingston, M., Mosheim, R., Williamson, J. 2011. Nitrogen in agricultural systems: Implications for conservation policy. United States Department of Agriculture Economic Research Service Proceedings. 1.
Ribaudo, M., Delgado, J.A., Livingston, M. 2011. Preliminary assessment of the potential for nitrous oxide offsets in a cap and trade program. Journal of Agricultural and Resource Economics. 40:1 - 6.
Herrera, J.M., Delgado, J.A., Dillon, M., Barbarick, K., Mcmaster, G.S. 2011. Accumulation of late-applied nitrogen and root dynamics during grain filling in irrigated spring wheat. Communications in Soil Science and Plant Analysis. 42:2235-2249.
Delgado, J.A., Khosla, R., Mueller, T. 2011. Recent advances in precision (Target) conservation. Journal of Soil and Water Conservation Society. 66:167A-170A.
Shumway, C., Delgado, J.A., Bunch, T., Hansen, L., Rubaudo, M. 2012. Best Nitrogen Management Practices Can Reduce the Potential Flux of Nitrogen Out of the Arkansas Delta. Soil Science. 177:198-209.
Essah, S., Delgado, J.A., Dillon, M., Sparks, R. 2012. Cover crops can improve potato tuber yield and quality. HortTechnology. 22:185-190.