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United States Department of Agriculture

Agricultural Research Service

Research Overview
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Cover Crops

The Columbia Basin of eastern Washington provides ideal conditions for high potato yields of up to 40 tons/acre. In the Basin, potatoes are grown on light textured soils that are low in organic matter and highly susceptible to leaching and wind erosion especially after harvest. Cover crops can play a vital role in filling open gaps in crop rotations where soil is left bare and further provide protective mulches under conventional tillage systems. The use of cover crops may serve as an alternative to fumigation as well as mitigating losses to soil and environmental quality.

Cover Crop

Additional benefits of cover crops in annual production systems include decreasing soil erosion, sequestering excess soil nitrogen, replenishing soil organic matter reserves, suppressing weeds and nematodes, increasing the size and activity of the soil micro-flora, as well as enhancing microbial populations antagonistic to pathogenic organisms (Figure 1). Various Brassica spp. and other cover crop systems have been evaluated in the PNW for their effects on individual crops, but research evaluating the impact of various cover crops on pest control and carbon and nitrogen dynamics in a total cropping system has not been conducted. Pest and nutrient problems are most effectively managed throughout the total cropping system rather than isolating a particular problem in an individual crop. Grasses and grains, because of their ability to quickly establish in the fall produce an extensive root system, that has been shown to be more efficient than legumes at capturing soil nitrate and preventing its late fall and winter leaching to ground water. Several studies have shown that certain cover crops (Sorghum sudanense, Brassica spp.) are also effective in reducing the incidence of pathogenic fungi, plant parasitic nematodes, and weeds  through the production of secondary plant compounds (cyanogenic and isothiocyanate compounds).

Soil Microbial Responses to Soil Fumigation and Mustard (Brassica hirta) Cover Crops in Potato Production Systems: On-farm trials demonstrated that fumigation significantly reduced selected soil pathogens and nematodes, but had minor affects on microbial functions. Although the mustard cover crop did not reduce the presence of plant pathogens, the incidence of disease caused by soil pathogens was not fully expressed and exhibited no reduction in tuber yield.



Nitrogen Transformation and Availability to Potatoes from Mustard Cover Crop: Mustard cover crop recovered 34 to 51% of the 50 lbs of 15N fertilizer applied. Nearly 30 % of the N in the cover crop biomass was taken up by the following potato crop. The mustard cover crop contributed 27 to 36 lbs N acre-1 towards the N requirement of a subsequent potato crop, saving farmers $19-25 / acre at current fertilizer prices.

Conservation Tillage

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. Potato production in irrigated regions typically occurs on soils low in organic matter that is highly susceptible to wind erosion when soils are left bare. Reduced tillage has had limited testing in irrigated potato production. Problems encountered in reduced tillage systems have been reduced crop yield, difficulty in planting, difficulty in controlling weeds, increases in weed pressure, and difficulty in harvest.  Modern herbicides have largely overcome the inability to manage weeds with reduced cultivation in potatoes. Commercial potato planters, hilling equipment, and reservoir tillage equipment however, are not designed to handle large amounts of crop residues. Tillage is primarily used in potato production to control weeds, facilitate planting, and increase the ease of later cultivation and harvest.  Reduced tillage has had limited testing in potato production systems under center pivot irrigation. 



Reduced Tillage in Potato Production: We developed reduced tillage protocols for potato production using standard field equipment an irrigated sweet corn/sweet corn/potato rotation. 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, including harvest. The eight year tuber yield average was not different between CT and RT, 37.2 and 36.4 T/acre, respectively.

Trace Gas Fluxes from Irrigated Sandy Soils within a Potato Based Crop Rotation: Nitrous oxide emissions accounted for 0.5% of the applied fertilizer to corn and 0.3% to potato; 60 and 76% lower, respectively, than the current estimated emissions factor of 1.25% used by the Intergovernmental Panel on Climate Change (IPCC). The lower emissions were due to split applications (“spoon feeding”) of N-fertilizer through the center pivot irrigation system during the growing season. This study was conducted within the GRACEnet network.

Organic Potato Production

Changes in Soil N pools and Microbial Activity Following Additions of Organic Amendments and Fertilizer Formulations: Organic production systems have been shown to modify the turnover of C and the formation of soil organic matter and stimulate nutrient cycling through enhancement of the soil microflora. The current ARS field trials involves the analyses of soil organic C, N, microbial characteristics and selected soil physical and crop quality measurements. The objectives of this study are to 1) evaluate the uptake of N by potato from a variety of organic sources and fertilizer formulations and 2) Quantify key soil agroecological processes (carbon and nitrogen cycling)


and application rates of organic amendments that

optimize physiological development (nitrogen capture,

plant growth rate) of potato under irrigated organic

cropping systems.

Effect of Foliar Applied Plant Elicitors on Microbial and Nematode Populations in the Potato Root Zone: Foliar applications of benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH) and the microbial protein, harpin reduced the nematode infection index of lesion and root knot nematodes but had no harmful effects on other soil organisms.


Yield Effects of Potato Common Scab (Streptomyces scabies) from Manure Applications.

The potential for utilizing dairy manure as a fertilizer

by reducing potential pathogen issues could create a significant market for dairy manure that could facilitate the export of nutrients off regional dairies and reduce purchased, fertilizer inputs for potato production. We demonstrated that the application of anaerobic

digested manure in absence of the pathogen reduced tuber yield 12%. Tuber yields of two potato cultivars

(Chieftain, Cal white) when grown with Streptomyces scabies decreased 15% to 32% depending on potato cultivar under low and high levels of the pathogen, respectively. The scab pathogen was shown to exert significant negative impacts on potato other than the formation of lesions that are unreported losses in production.


Carbon Farming

BioEnergy Research-Oilseeds: Biodiesel

·         Develop and evaluate bioenergy crop production options in irrigated specialty crop rotations and utilize the byproducts of bioenergy production to control weeds and disease and enhance soil quality.


Oilseeds: Biodiesel

Sustainability is a requirement for all new biobased technologies. Sustainability is dependent upon; acceptable environmental impacts of products; economic viability for all participants; and a positive social impact of the product and its production. We have initiated a series of studies evaluating a number of oilseed crops grown to maturity for an emerging biodiesel market and how they will fit into current high value irrigated vegetable cropping systems. We are evaluating five oil seed crops that can be grown in the PNW, as well as, nationally. These include: spring and winter rapeseed, mustard, sunflower, safflower and camelina.

Fig. 1. Winter canola in mid-March under center pivot irrigation near Othello, Washington (photo by Becky Lyle).


Our data indicates that it will require approximately 30,000 acres to support a 5 M gal biodiesel facility using such crops as safflower or winter rapeseed. In the Midwest, production of biodiesel using soybeans averages 1 M gallons on equivalent acreage. The developing U.S. bioenergy market is an opportunity for PNW growers to fill a feedstock production niche. The use of petrodiesel in the U.S. averages about 43 billion gallons a year. The U.S. currently has an oil supply problem with the Middle East, as well as competition from developments in China and India. U.S. agriculture can add to the fuel pipeline by producing biodiesel which would have significant impacts on local economies.”


Oilseed Production under Deficit Irrigation and Variable N Fertilization The production of oilseed crops represents a unique opportunity for PNW producers to provide a biodiesel feedstock for a renewable energy industry. The inclusion of oilseeds in rotation offers producers an additional strategy to improve farm economies and gain additional benefits that improve soil and water conservation, reduce pest cycles, and diversify cropping systems. Canola, rapeseed and safflower can supply oil for the emerging biofuel industry. Oilseed yields under deficit irrigation (70-80% of ET) ranged from 3000 to 4500 lbs with oil concentrations of 35 to 40% depending upon crop variety and year of production.

Safflower under deficit irrigation.




BioEnergy Research-Perennial Biomass Crops: Ethanol

Perennial Biomass Crops: Ethanol

Hal Collins,
Rick Boydston
Ashok Alva
S. Fransen

   Another group of bioenegy crop we are studying are residues and perennial warm season grasses like switchgrass. About 90% of the domestic ethanol feedstock supply is derived from corn grain (Zea mays L.). Reasons for having selected corn include: 1) corns’ high starch content which can be rapidly distilled to alcohol, 2) corns’ higher distillation efficiencies are greater than most other feedstocks, 3) most of the ethanol produced is in the mid-West where corn is widely grown, and 4) many refineries are located in the Gulf Coastal States, close to current ethanol distillation centers.

Total dependence of the ethanol market on corn has inherent problems in sustaining feedstock supplies including: 1) as a warm-season crop, corn cannot be grown in all areas, such as those with short growing seasons or low rainfall, 2) corn requires high inputs of fertilizers, herbicides and insecticides to ensure high yields, 3) as an annual crop, corn grown under rain-fed conditions has yield potentials varying significantly from “bin busters to empty bins”, making it risky to grow due to the uncertainty of shifts in rain fall as a result of global climate change, and 4) wind erosion of soils resulting from annual cropping is a major problem in the arid west.
        Switchgrass is adapted to the warmer and irrigated regions of the Pacific Northwest (PNW) and therefore a viable alternative to corn. Switchgrass contrasts to corn in the west by: 1) being a perennial crop, eliminates the need for annual tillage, reducing soil loss from wind erosion, 2) having lower fertilizer requirements, and fewer pest issues decreases fertilizer and pesticide use, 3) ability to produce a harvestable biomass and becoming dormant if irrigation water is restricted compared to corn which would senesce and produce little harvestable yield, and 4) since 2001, switchgrass has proven to be productive and adapted to the lower Columbia Basin region of the PNW in joint ARS/WSU research trials. To be economical for the grower and local ethanol production facilities, a low-cost, high-return sustainable crop is required. Many questions surround the feasibility of switchgrass as an ethanol feedstock in the PNW.

Research yields of switchgrass have ranged from  22 to 30 Mg dry matter per hectare depending upon the cultivar grown. At these sustained yields 7-10,000 hectares would be needed to support a 75 million L per year. When placed in context of the energy return balance of 4.4 and 1.2 (energy output:input ratio) for switchgrass and corn, respectively, corn will be a more expensive feedstock than switchgrass. Comparatively, irrigated corn producers currently grow high yields of grain while our switchgrass research indicates a significant potential for crop improvement and improved ethanol yields.

To produce sustainable feedstocks as alternative energy supplies in the PNW we would likely see a shift from less profitable crops to those that meet feedstock demands while increasing grower returns. 


Carbon Sequestration under Irrigated Switchgrass: 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. Switchgrass production in the warmer irrigated regions of the PNW is a viable bioenergy feedstock producing greater than 12 tons dry matter per acre. Switchgrass production improved soil C reserves; 1.5 tons per acre with an average 15% increase in soil C after three years. This information is useful in the development of secondary markets such as C-credit trading.

Carbon Sequestration and Greenhouse Gas Emissions from the Sustainable Intercropping of Switchgrass and Hybrid Poplar for BioEnergy:  

     This five year research project addresses the “Carbon Sequestration and Sustainable Bioenergy Production” Program Area Priority of the Sustainable Bioenergy Research Program A6121. The overall goal of the project is to quantify biofuel energy biomass production potentials, C sequestration and greenhouse gas emissions within a switchgrass-hybrid poplar intercrop system.

     The objectives are to: 1) Determine the influence of poplar varieties of contrasting leaf area index and canopy architecture on switchgrass biomass production. 2) Determine changes in soil C cycling and C sequestration; 3) Monitor greenhouse gas production and; 4) Produce lifecycle analyses on all aspects of the production chain within an intercropped poplar switchgrass production system.

    The benefits and outcomes include: utilizing local animal waste streams; sustainable reductions in biofuel feedstock production costs; improved environmental quality through increased C-sequestration and reduced greenhouse gas emissions. Our approach of intercropping switchgrass within a perennial non-food crop (poplar) will alleviate “food for fuel” concerns.  Adoption of this intercropping strategy will replace 49 M L of fossil fuels per year and sequester >5,250 Mg C per year in the Pacific Northwest.



Nutrient Removal by Switchgrass Grown for Bioenergy: Perennial herbaceous bioenergy crops have the potential to improve soil quality, sequester soil C, enhance nutrient cycling improve wildlife habitat, and supply a portion of U.S. energy needs when used as a fuel. Removal of plant biomass removes substantial soil/plant nutrients. Assessments of the export of nutrients off-farm showed removal of 200 lbs N per acre; 40 lbs P per acre; 310 lb K per acre; and 15 lb S per acre. ARS-Prosser data indicate that future bioenergy refineries need to develop technology to recover plant nutrients for return to production fields.


2011 Biomass Biofuel Feedstocks

BioEnergy Research-Biochar



Influence of Biochar on Soil pH, Water Holding Capacity, Nitrogen and Carbon Dynamics:

The thermo-chemical conversion (pyrolysis) of plant biomass is being evaluated by ARS for its potential to produce second generation liquid biofuels and the co-product biochar, which can be used as a soil amendment. Biochar was found to improve soil pH, water holding capacity (WHC) and soil C pools. In irrigated production systems, appropriate choice of biochar feedstock could increase soil WHC and reduce either the frequency or amount of irrigation.


Remediation of Phosphorus from Dairy Lagoon Waters using Biochar:

Estimates of animal manures produced in the United States by feedlot cattle, dairy cattle and swine exceeds 78 million tons annually. ARS-Prosser developed a strategy to utilize dairy waste as an alternative energy and fertilizer source. The fiber component exiting an anaerobic digester was used as a feedstock to produce bio-gas or bio-oil under low temperature pyrolysis. The co-product, biochar was applied to dairy waste water to remove nutrients. Our approach resulted in the removal of >32% of the P from the dairy effluent. Dairies in Washington State could produce 230,000 tons of biochar a year from manure.

Phosphorous Uptake by Potato from Biochar Coated with Anaerobic Digested Effluent: Removal of nutrients by biochar from dairy storage lagoons and use as a supplemental fertilizer off site is a beneficial strategy to reduce nutrient contamination around dairies and supply nutrients in potato production. Biochar amended with dairy effluent applied at 2.5 T per acre maintained recommended soluble P levels (1000 ppm) in Ranger and Umatilla potato variety petioles through 60 days after emergence. Biochar amended-P from dairy lagoons can be used successfully as a P fertilizer supplement in potato production. Secondary benefits of biochar additions improve soil pH, water holding capacity and soil C pools.


2011 Biochar

Last Modified: 4/5/2012