2008 Annual Report 1a.Objectives (from AD-416) 1)Determine the effects of reduced tillage and fall-planted cover crops in irrigated potato production systems on weed dynamics and develop weed management strategies that minimize the negative impacts of weeds. 2)Understand the processes controlling soil biological activity and community structure of the:(i)soil micro-flora, (ii)plant pathogens, (iii)nematodes, and (iv)insects under reduced tillage and cover crops in irrigated potato production systems. 3)Determine and understand the mechanisms controlling carbon and nitrogen cycling and trace gas fluxes under reduced tillage in irrigated potato production systems. 4)Evaluate potato crop performance, potato tuber quality, soil fertility and nitrate leaching below the rootzone under variable rates of preplant and inseason N applications under conventional and reduced tillage. 5)Evaluate the soil and plant growth parameters of a potato growth model, and validate the model for major potato cultivars and different management practices. 1b.Approach (from AD-416) 1)A standard and reduced tillage practice will be evaluated in a 3-year crop rotation of field corn/field corn/potato. The experimental design is a randomized strip split plot design with 4 replications, and includes 4 N treatments in each tillage treatment. The treatments consist of preplant N application rates of 56, 112, and 168 kg N ha-1 with remaining N (total N at 336 kg ha-1) applied as inseason fertigation beginning 3 weeks after emergence. 2)A 4-year crop rotation of winter wheat/sweet corn/sweet corn/potato and cover crop treatments will be investigated. Cover crops include white mustard, winter wheat, and oat-hairy vetch. 3)In a parallel experiment, the effects of different rates of preplant N and rates and frequencies of inseason N application on the tuber yield and quality of Ranger Russet and Umatilla Russet cultivars will be investigated. In all the above trials, effects of various treatments on:(i)microbial diversity and activity; (ii)nitrogen transformation, uptake, and losses; (iii)weed management; (iv)pathogens and nematodes populations; (v)gas fluxes; (vi)nutrient cycling and soil quality will be evaluated. 4)The data will be used to develop decision support systems for sustainable management of irrigated potato rotation system. Formerly 5354-13610-002-00D (11/03). 3.Progress Report Objective 1. Potato is produced on approximately 160,000 acres in the Columbia Basin of Washington on highly erodible, low organic matter soils. Weeds and their control cost growers from $35 to $200/acre. Utilizing Brassica and rye cover crops, when combined with herbicide banding and cultivation, reduce herbicide inputs 66%. As a result of this research Washington potato growers are currently planting Brassica cover crops on over 25,000 acres. Volunteer potatoes are difficult to manage weed in regions where mild winter temperatures fail to kill tubers left in the ground after potato harvest. The critical temperatures and time of exposure required to kill potato tubers were identified, leading to development of a prediction tool for volunteer potato severity. Growers using these management strategies can save up to $250/acre in hand weeding costs and reduce sources of late blight, green peach aphid, and corky ringspot disease. Objective 2. High costs of synthetic soil fumigants and potential loss of soil microbial functions have concerned potato growers. As an alternative we have used mustard cover crops containing high glucosinolate concentrations as green manures to reduce soil pathogens and offset fertilizer and chemical costs. Fumigation significantly reduced selected soil pathogens and nematodes, but only minimally affected microbial functions. We showed that a mustard cover crop recovered 34 to 51% of applied fertilizer with 29 % of the N in the cover crop available to the following potato crop. Growers can budget 30 to 44 kg N ha-1 present in the cover crop as a source of N to the potato crop and save $14-20 ha-1 at current fertilizer costs. Objective 3. We developed reduced tillage protocols using contemporary equipment and measured the impact of reduced tillage on potato yield, soil organic matter dynamics, and trace gas fluxes. The new tillage strategy reduced the total number of passes across the field from nine to six and soil disturbance operations from seven to four compared to conventional tilled potato treatments. For sweet corn, soil disturbance and field operations were reduced 100%. Crop yields and soil microbial characteristics were not changed by using reduced tillage. We found minor losses (0.4%) of the applied fertilizer as N2O from irrigated potato fields. Growers can account for 1 to 7% of the N-fertilizer applied as gaseous N2O loss depending on the form of fertilizer applied. Research is part of the USDA-ARS GRACEnet project. Objective 4 and 5. Research on potato N management was completed using ‘Russet Burbank’ and ‘Umatilla Russet’ cultivars grown in the Pacific Northwest. Results demonstrated that N application in excess of 336 kg·ha-1 rate did not show beneficial effects in terms of total tuber yields, or yields of different size grade tubers. Frequency of in-season N application (5 to 20 applications) did not show a significant effect on either the tuber yield or quality. Contribution of available N from soil organic N and N from prior crop residues accounted for 85, 83, 75, 59, and 44 mg·kg-1 soil for sweet corn, alfalfa, field corn, wheat, and potato residues, respectively. NP 216,Comp.3 4.Accomplishments 1. Mustard seed meals inhibit weeds. Weeds are the primary limitation and expense to organic onion and peppermint production. Mustard (Sinapis alba) seed meal, byproducts of oil extraction from the seeds, contain glucosinolates that release compounds that inhibit weed germination and establishment. Mustard seed meal applied by ARS scientists in the Vegetable and Forrage Crops Production Research Unit in Prosser, WA at 1 ton/acre at specific stages of organic onion and peppermint growth controlled annual weeds for about 3 weeks without significant injury to either crop. Use of mustard seed meal may be useful to producers of organic crops for weed suppression and help reduce excessive costs of hand weeding which can range from $500 to $2,000 per acre. NP 216 Component III. Examples of Integrated Agricultural Systems in ARS f. The Management Improvement Program. 2. Conservation tillage in potato. Adoption of conservation tillage in irrigated potato cropping systems has been limited due to a perception of poor crop stands, increase in disease and pest problems and the high cost to replace equipment. Intensive agriculture and increased N-fertilizer use have also contributed to elevated emissions of the greenhouse gases, CO2, CH4, and N2O. The new tillage strategy by ARS scientists in the Vegetable and Forrage Crops Production Research Unit in Prosser, WA reduced the total number of passes across the field from nine to six and soil disturbance operations from seven to four, including harvest, compared to conventional tilled potato treatments. For sweet corn, soil disturbance field operations were reduced 100%. This new tillage strategy means that growers can account for 1 to 7% of the N-fertilizer applied as a gaseous N2O loss depending on the form of fertilizer applied. NP 216 Component III, Integrated Nutrient and Water Management. No Problem area 3. Carbon Sequestration under Irrigated Switchgrass. Current USDA initiatives and research opportunities (Biomass Research and Development Initiative, 2007 (USDA/DOE)) show the need for new research evaluating the impacts of producing bioenergy biomass crops or removing select crop residue components for bio-fuel production. Perennial herbaceous bioenergy crops have the potential to sequester soil C, supply a portion of U.S. energy needs, and reduce atmospheric CO2 enrichment when used as a fuel. This research by ARS scientists in the Vegetable and Forrage Crops Production Research Unit in Prosser, WA showed that switchgrass (Panicum virgatum) production in the warmer irrigated regions of the Pacific Northwest is a viable bioenergy feedstock, can improve soil quality and sequester C in soil. Above ground biomass yields averaged 20.4, 16.9, and 14.5 metric tons dry matter per hectare per year for Kanlow, Shawnee, and Cave in Rock cultivars, respectively. The C-sequestration potential of switchgrass and its below ground productivity averaged 3.0 metric tonnes per hectare with an average 15% increase in soil C after three years. This data will be useful in the development of secondary markets such as C-credit trading or by ethanol producers interested in nutrient recovery for production of fertilizers or animal feed supplements. NP 216 Component III, Sustainable and Organic Farming. 5.Significant Activities that Support Special Target Populations None 6.Technology Transfer Number of Non-Peer Reviewed Presentations and Proceedings 10 Number of Newspaper Articles and Other Presentations for Non-Science Audiences 2 Review Publications Hamm, P., Boydston, R.A., Hoy, C.W., Stevenson, W.R., Hutchinson, P. 2007. Applying Pesticides in Potato Health Management, ed. D. Johnson. APS Press. Potato Health Mangement 2nd Edition APS Series. Chapter 13, Pg 113-122. Boydston, R.A., Vaughn, S.F., Collins, H.P. 2008. Response of weeds and ornamental plants to potting soil amended with dried distillers grains. HortScience. 43:191-195. Mojtahedi, H., Boydston, R.A., Crosslin, J., Brown, C.R., Riga, E., Anderson, T.L., Spellman, D.E., Quick, R.A. 2007. Establishing a Corky Ringspot Disease Plot for Research Purposes. Journal of Nematology. 39(4):313-316. Metzger, C., Boydston, R.A., Ferguson, H., Williams, M., Zack, R., Walsh, D. 2008. Interactions between population density of the Colorado potato beetle, Leptinotarsa decemlineata, and herbicide rate for suppression of solanaceous weeds. Journal of Insect Science 8:38. Available: http://www.insectscience.org/papers/2008/. Boydston, R.A., Vaughn, S.F., Anderson, T.L. 2008. Mustard (Sinapis alba) Seed Meal Suppresses Weeds in Container Grown Ornamentals. HortScience. 43:800-803. Boydston, R. A. 2008. The Canon of Potato Science: 19. Non-parasitic Weeds. Potato Research 50:279-282. http://dx.doi.org/10.1007/s11540-008-9075-4. Williams, M., Boydston, R.A., Davis, A.S. 2008. Differential tolerance in sweet corn to wild proso millet (Panicum miliaceum) interference. Weed Science. 56:91-96. Boydston, R.A., Mojtahedi, H., Crosslin, J., Brown, C.R., Anderson, T.L. 2008. Effect of hairy nightshade (Solanum sarrachoides) presence on nematode, disease, and insect pests of potato. Weed Science. 56: 151-154. Haile-Mariam S., H.P. Collins, and S.S. Higgins. 2008. Greenhouse Gas Fluxes from an Irrigated Sweet Corn (Zea mays L.) - Potato (Solanum tuberosum L.) Rotation. J. Environ. 37:759-771. Haile-Mariam, S., H.P. Collins, S.E. Wright, and E.A. Paul. 2008. Fractionation of soil organic matter following long-term laboratory incubation. Soil. Sci. Soc. Am. J. 72:370-378. Alva, A.K. 2008. Set points for potato irrigation using real-time continuous monitoring of soil water content in soil profile. J. Crop Improvement. 21:117-137. Alva, A.K. 2008. Water management and water uptake efficiency by potatoes. Archives of Agronomy and Soil Science. 54:53-68. Liu, G., Y.C. Li, and A.K. Alva. 2007. Moisture quotients for ammonia volatilization from four soils in Potato production regions. Water, Air, and Soil Pollution. 183:115-127. Sajwan, K.S., S. Paramasivam, A.K. Alva. 2007. Effects of different rates of fly ash and sewage sludge mixture amendments on cation availability and their leachability. Journal of Environmental Science and Health, Part A 42:1155-1160. 2007. Liu, G., Y Li, and A.K. Alva. 2007. Temperature quotients of ammonia emission of different nitrogen sources applied to four agricultural soils. Soil Science Society of America Journal. 71:1482-1489.