Development of Sustainable Potato Production Systems for the Pacific North West

1991 Annual Report for LW91-029

Project Type: Research and Education
Funds awarded in 1991: $330,000.00
Projected End Date: 12/31/1993
Matching Non-Federal Funds: $428,000.00
Region: Western
State: Idaho
Principal Investigator:
Jeffrey C. Stark
University of Idaho

Development of Sustainable Potato Production Systems for the Pacific North West


1.Collect and compile existing information on sustainable production practices for potato rotations and identify additional research and information needs.
2.Determine the effects of alternative rotation crop management practices on crop yield and quality, and weed, insect and disease populations and development.
3.Determine the feasibility of using green manure rotation crops and cover crops to reduce reliance on synthetic nitrogen fertilizer in potato rotations and reduce nitrate leaching and erosion.
4.Inform and train growers, field advisors and extension agents on the short and long term effects of sustainable crop management practices and on approaches for converting to sustainable systems.
5.Develop decision support system components that will assist producers in evaluating alternative production practices in terms of sustainability, environmental quality and profitability.

Abstract of Results
The initial draft of an information guide on alternative management practices for potatoes has been completed. The guide cites references on alternative cultural, nutrient, and pest management practices. The initial draft of a Pacific Northwest production manual for sustainable potato production systems is in the final stages of preparation. The manual will provide producers with information on the agronomic, economic, and environmental effects of alternative potato production practices, as well as approaches for converting to alternative management systems.

Potato growers in Idaho and Washington were surveyed to determine current production practices, major pest problems, levels of pesticide use, and information on production costs and yields. Survey results indicate a heavy reliance on herbicides, fungicides, and insecticides by the majority of potato growers. However, there was also significant interest in alternative pest control methods. Compared to conventional growers, organic growers placed greater emphasis on variety selection, crop rotation, green manures, and utilized a much wider variety of pest control strategies.

A number of alternative management practices have been used effectively in on-farm tests to control pests and supply nutrients to potatoes. Several mineral and biological compounds have been successfully used to selectively control Colorado Potato Beetle without producing any environmental contamination.
Rapeseed grown as a winter cover crop has reduced weed biomass from 50 to 96 percent in the following potato crop. White mustard green manures have also greatly reduced weed populations in potatoes. Studies have shown that by adding one post-hilling cultivation, potato growers should be able to reduce the total amount of herbicide applied by about 25 percent. Rapeseed, white mustard, sweet corn, and sudangrass have been successfully used to improve control of nematodes and soilborne potato diseases. Incorporation of sweet corn residues following harvest reduced Verticillium wilt in potatoes by 37 to 41 percent and increased marketable yields by 50 to 66 percent compared to previously fallowed fields. Following sudangrass green manures, Verticillium wilt of potato was reduced by 24 to 29 percent and U.S. No. 1 potato yields were increased by 24 to 38 percent compared to potatoes following barley or fallow. Rapeseed and sudangrass green manures provided up to 72 and 86 percent control, respectively, of root-knot nematode in the following potato crop. These results show that selected green manure and cover crops have considerable potential for reducing reliance on herbicides, fungicides, and fumigants.

Single season legume green manures such as Nitro alfalfa, Austrian peas, and hairy vetch have provided 80 to 100 percent of the nitrogen required by the following potato crop. If these crops are harvested to provide an additional economic return to the grower, the amount of nitrogen contributed to potatoes is reduced by about 40 percent. Nitrogen mineralization patterns for Nitro alfalfa and Austrian pea residues incorporated by fall plowing synchronized reasonably well with potato nitrogen uptake patterns. This resulted in relatively high nitrogen use efficiency and minimal nitrate leaching potential. On-farm tests conducted by growers showed that the inclusion of alfalfa hay or pea green manure in grain-potato rotations increased marketable potato yields by 8 to 18 percent with greatly reduced conventional fertilizer inputs.

A summary of an analysis of enterprise budgets for 18 matched conventional and organic farming systems shows that average material costs were lower for the organic systems, while labor costs were higher. However, there were no significant differences in overall fixed and variable costs or projected net returns for the two systems. Additional economic analyses of a number of alternative potato farming systems were also completed. Evaluating the farming systems on a rotational basis showed a significant economic benefit from including alfalfa or peas in grain-potato-grain rotations.

A computerized plant nutrient diagnosis and recommendation system was developed for crops grown in potato rotations. Use of the program should lead to more efficient use of plant nutrients and a reduced potential for nitrate leaching.

Potential Contributions
Nutrient Management. Results of this project show that alternative nutrient management practices can be practical and cost effective. Nitrogen fertilizer costs for commercial potato production in the Pacific Northwest range from about $75 to $135 per acre. Legumes grown as green manures can provide 80 to 100 percent of a subsequent potato crops nitrogen requirement, while harvested legumes can provide about 40 to 60 percent. Animal manures can supply sufficient nutrients to produce a high yielding potato crop and are often very low cost.

Pest Management. Fumigation of potato fields for nematode and Verticillium wilt control typically costs more than $200/acre. Rapeseed and sudangrass green manures grown prior to potatoes have provided up to 86 percent control of root-knot nematode, while sudangrass has reduced Verticillium wilt by 25 to 50 percent. Residues incorporated from a harvested sweet corn crop can significantly reduced Verticillium wilt and increase marketable yield of potatoes. Rapeseed cover crops also can reduce or eliminate herbicide applications in potatoes ($30 to $45/acre) without affecting yields. Depending on the weed species infesting a field, 0.5 to 7.5 lb/acre of herbicide could be eliminated by cultivation.

Economics. Analyses of alternative potato farming systems on a rotational basis show that adding crops such as peas, alfalfa, and canola to traditional grain-potato rotations can be cost effective.

Operational Recommendations
In areas with a relatively long growing season such as Western Idaho and the Columbia Basin in Washington, fall-planted legume cover crops can be a practical and cost effective means of supplying nitrogen to potatoes. However, in areas with shorter growing seasons such as eastern Idaho, fall-planted legume cover crops will likely not produce sufficient growth and nitrogen accumulation to provide adequate nitrogen for the following potato crop. In these areas, full-season cropping to legumes prior to potatoes should be considered. Delaying residue incorporation until the following spring should result in more efficient use of the legume nitrogen. Harvesting the legumes for hay or seed will reduce nitrogen contributions to potatoes by about 40 percent compared to green manure incorporation.

Yields of potatoes fertilized with a combination of animal manures and fall-planted green manures were similar to those of potatoes fertilized with conventional fertilizer sources. In many cases, animal manures were available at a relatively low cost. Potato growers should investigate the local availability of animal manure sources and consider the feasibility of including manure or compost application in their management system.

Potato growers rely heavily on high rates or sequential applications of herbicides for weed control because of the concern that root pruning resulting from cultivation will reduce marketable yields. Data from this project show that hilling plus one cultivation does not reduce marketable yields. Therefore, growers may be able to reduce herbicide applications by 25 percent or more if one cultivation was added to their weed management program. Growing full-season or fall-planted Brassica species such as rapeseed or mustard prior to potatoes should also help suppress weed populations and reduce the heavy reliance on herbicides.
Lengthening rotations and including rapeseed, mustard, or sudangrass as rotation crops or winter cover crops shows considerable potential for reducing reliance on fungicides and fumigants for disease and nematode control, while still maintaining an economically-viable farming system.
Reported in 1995