Assessment and Demonstration of the Sustainability of Long vs. Short Potato Rotations

Project Overview

Project Type: Research and Education
Funds awarded in 2005: $179,403.00
Projected End Date: 12/31/2006
Region: Western
State: Idaho
Principal Investigator:
Bryan Hopkins
University of Idaho

Annual Reports


  • Agronomic: potatoes


  • Crop Production: crop rotation
  • Soil Management: soil analysis, soil quality/health

    Proposal abstract:

    Potatoes are a relatively high income potential crop and, as a result, many growers respond to economic pressures by shortening the time between when they grow this crop. A farm must generate a certain amount of revenue each year above expenses in order to service debt, invest in equipment, and meet family expenses. Because potato prices have declined while costs have increased, the margin on potatoes has declined steadily in recent years. Growers need to farm more acres or farm existing acres more intensively to generate needed revenue. Potato growers also seek to spread the high cost of equipment over more acres. If more acres cannot be acquired, growers shorten rotations to increase potato acreage and lower per acre machinery ownership costs. Increasing the frequency of potatoes in a rotation might seem to increase profitability, but this may not be reality when long-term negative consequences are considered. An extended period of time between potato crops interrupts the life cycles of many pests destructive to the potato plant. Alternatively, short rotations require increased expenditures for pesticide usage due to increased pressure from weeds, insects, disease, and nematodes. Furthermore, potato production places a relatively high nutrient demand on the soil and, as a result, short rotations require increased fertilization expenditures. Additionally, it is possible with most crops to have little or no tillage, but potatoes generally have pre-season ground preparation, in-season cultivation, and end-of-season harvest activities that severely disturb the soil and, as a result, contribute to a decrease in soil organic matter and an increase in soil compaction and erosion. These soil- and pest-related factors associated with short rotations result in increased expenses and decreased income due to reduced yield and tuber quality. Not only do growers generally fail to consider these costs, but they also fail to account for increased land and equipment costs associated with decreasing the frequency between potato crops. Consumer appeal is also an issue associated with poor quality tubers and affects the profitability of the entire potato industry. Individual researchers have documented many of these issues, but most studies have been short-term, focused on one crop and, consequently, are limited in scope. In actuality, the true effects and costs of rotations are dependent upon the entire cropping system and take many cropping cycles to come to equilibrium (having been in either a long or short potato rotation for a period of time sufficient for the positive or negative effects to have materialized). Studies that occur over just a few years and/or evaluate only part of the system cannot provide adequate information on the total costs of short rotations. The overall objective of this project is to bring growers together with scientists in a multi-state, interdisciplinary effort to examine the long-term economic, agronomic, and environmental sustainability of short vs. long potato rotations. This objective will be met by intensively studying pest and soil relationships in 108 paired fields over three years, with pairs consisting of one field each of a long and a short rotation history. This project is unique because the data collected and disseminated will be from whole fields already equilibrated over many years, as opposed to the traditional approach of initiating and quantifying treatment effects within the relatively short time period of a typical research project.

    Project objectives from proposal:

    1. Outcomes – Impacts:
    a. Increasing producer knowledge, awareness, attitudes, and skills: An anticipated outcome of this project is an increase in producers’ awareness of the costs of shortening potato rotations. They will receive tools and training in order to use this information as they make cropping system decisions on their farms. It is generally asserted that shortened potato rotations result in losses in soil quality and tuber yield, size, grade, and storability, as well as increased pesticide, fertilizer, and equipment usage. It is anticipated that the research portion of this project will substantiate and quantify these assertions, giving growers needed information to more accurately calculate their budgets. Developing and relying on accurate cost of production figures will enable growers to make proper management decisions needed to achieve efficiency and to maintain competitiveness in a market-based economy. The bottom-line is that growers will learn how to achieve a more environmentally and economically sustainable production system based on sound agronomic principles. These outcomes will be measured by assessing the number of acres switched from short to long rotations. Growers involved in the project (both field and workshop participants) will be surveyed annually to track whether they are making crop rotation decisions by adopting the use of the crop enterprise budget information developed in this project.
    b. Information dissemination: The study results and “model” growers will be highlighted at the WSU Potato Field Days and at the UI Sustainable Potato Production Field Days. Based on previous attendance figures, well over 100 growers and their advisors will be exposed annually to this information. The information will also be published on the UI Potato Cropping Systems web page and linked with other university and sustainable agriculture websites. Press releases will be distributed annually to advertise the research findings and educational resources generated by this project. Workshops at the Idaho, Oregon, and Washington Potato Conferences will be conducted in year 3 (possibly year 2 as well) to provide growers and farm managers with project information and training on the use of the University of Idaho’s Crop Enterprise Budget Worksheet (CEBW) program. This will allow them to more easily generate accurate cost of production estimates using their own farm data on rotation-specific scenarios and will provide them with a management tool to help them assess the rotation-specific impact on operating and ownership costs. The CEBW program will be available to producers on CD as well as from the UI Agricultural Economics and Rural Sociology website. The most effective information dissemination tool will be the one-to-one consulting with growers and their crop advisors at the hands-on workshops and with those participating directly in the project.
    Final results will be presented during a Soil Quality & Pest Management Symposium at the Idaho Potato Conference and the proceedings published as a Pacific Northwest (PNW) Extension Bulletin. The practical aspects of this project will be published in various popular press magazines and extension publications, including: Spudvine, Western Farmer Stockman, Potato Grower, Spudman, Potato Country, Vegetable Grower, etc. The summarized scientific findings of the project will be published in the Journal of Sustainable Agriculture or the Journal of Agricultural Systems. Depending on research results, individual discipline publications may also be pursued in the Journal of Extension, Western Economics Forum, Soil Science Society of America Journal, Journal of Environmental Entomology, Plant Disease, Journal of Nematology, Weed Technology, and American Journal of Potato Research.
    c. Resources impacted: It is generally known that increasing the time between potato crops will result in reduced pesticide and fertilizer needs. Although most people believe that judicious pesticide and fertilizer use is appropriate and necessary, there is an associated risk to people and natural resources. Reducing pesticide use will lessen potential risks to farm workers, livestock, fish, wildlife, beneficial soil microbes, and the public. Additionally, increasing the use of crops that more efficiently scavenge soil nutrients, such as small grains and alfalfa, in the potato cropping system may reduce the use of fertilizer resources, as well as decrease the risk of water contamination with nitrates, phosphates, and other nutrients that can become problematic when present in excess. In addition to reduced risk to natural resources, decreasing pesticide use also will lengthen the availability of currently available pesticides by slowing the rate of pesticide resistance development, giving growers continued access to effective and inexpensive pesticides that can be used judiciously. Furthermore, potato production is energy expensive due to high demand for irrigation and equipment fuel and indirect energy expenditures associated with producing fertilizers/pesticides.
    Moreover, since potato production results in significant soil disturbance, increasing the time between potato crops will decrease the risk of soil erosion and breakdown of stabilizing soil aggregates. Adoption of practices that prevent soil carbon loss will also help growers become eligible for conservation payments in the Conservation Security Program.
    Overall, the aims of this project are to not only increase environmental sustainability, but also to have a positive benefit on the rural communities that are still highly dependent on potato cropping systems for their economic well-being.
    d. Positive economic impact (in dollars): The main economic question that will be answered with this study is: Does the improved net return of a potato crop in a long rotation cycle overcome the reduced income potential when growing lower value rotation crops more years during the rotation cycle? The project will also evaluate trade-offs between higher operating costs from shorter rotations with the conversely lower ownership costs. There are other questions that are more difficult to quantify that will not be addressed directly in the research phase of this project, but will be addressed in the education phase. These issues, related to short rotations, are increased topsoil loss and pesticide risk to farm workers and the environment.
    Longer rotations are generally consistent with increased agricultural sustainability, which makes farm communities more economically viable. Potatoes contribute significantly to the economy of the Pacific Northwest. PNW potatoes have a farm market value of $1.3 billion, based on a three-year average. Potatoes support significant processing and fresh pack operations as well as manufactures of specialized potato equipment. The PNW states have approximately 80 percent of the potato fry plant capacity in the U.S., over 90 percent of the dehydration plants, and ship 40 percent of the table stock potatoes in the U.S. An estimate of the total economic contribution of potatoes to the region’s gross product is in excess of $4.5 billion. It is paramount to the economic stability of the PNW region to find sustainable ways of producing potatoes to compete in a global economy. Furthermore, potatoes are of importance in other states falling under the WSARE area (Colorado, California, Montana, and even Alaska), as well as many other states in other regions of the U.S. and in most other countries. As such, the outcomes of this project will be applicable to global potato production, as well as sustainable rotations in general.
    2. Producer involvement: Producers are the driving force behind this proposal. The Idaho Potato Commission (IPC) has stated that lengthening rotations is part of their strategic plan to help improve the quality of potatoes produced and the resulting consumer appeal. The UI Potato Cropping Systems Advisory Board (growers, independent consultants, and industry representatives) has recognized an increasing problem in fields with short rotations. They are frustrated, however, that only small plot, short-term data exist to quantify the detrimental effects of relatively short rotations. As a result, growers often make decisions based on short-term economics that are overly optimistic with regard to yield/grade expectations and do not include long-term costs that impact sustainability.
    Producers have been and will continue to be involved in every phase of the project. Close cooperation with 18 to 36 growers and their crop advisors/managers will be required annually to identify fields that have consistent, long-term cropping sequence histories. (Ideally one grower will provide a pair of fields, but it is doubtful that 18 growers can be located who have fields with both long and short rotation histories and so separate growers may need to be used for each pair of fields, resulting in as many as 36 grower cooperators.) Growers assisting in the project will provide information on crop progress and will receive valuable, timely information in the form of analytical and scouting results during the cropping season. At the end of each annual phase, the information will be disseminated to producers in a cooperative effort with the growers, researchers, and educators guiding this project. The IPC and the Potato Growers of Idaho are also planning to disseminate information regarding length of rotation in cooperation with this project. Growers and their crop advisors will be involved in the workshops and the popular press articles. Finally, according to the UI Potato Cropping Systems Advisory Board, the most effective way to facilitate adoption of new management techniques is to highlight growers successfully using these practices in whole-farm systems and, as such, this technique will be used extensively in this project.
    3. Project relevance: Impacting the environmental and rural economic sustainability of the PNW requires focusing on the major cropping systems in this tri-state region. Potatoes are of primary economic importance in the PNW, where approximately 50% of the U.S. production of this important crop is grown. Short-term cash flow pressures are resulting in growers decreasing the frequency between the times that they rotate to the relatively high income potential potato crop. Detrimental consequences of a short vs. a long potato rotation are substantial and complex. The impacts of shortened potato rotations include reduced crop residue, soil biodiversity, soil structure, soil carbon sequestration, nutrient availability, and overall soil quality, as well as increased pesticide use, pesticide resistance development risk, and soil erosion. These impacts result in reduced environmental and agricultural sustainability.
    Furthermore, decreased soil quality and increased pest pressure generally results in reduced potato yields, size, quality, storability, and consumer appeal. Although many of these parameters have been examined individually over the short-term, the long-term, integrated effects of potato cropping system variables on the chemical, physical, and biological properties of soil need to be studied and demonstrated in a comprehensive cropping systems approach. This project addresses this need and all national and regional SARE goals, in that it promotes farming methods that: 1) strengthen agricultural competitiveness, 2) satisfy human food needs, 3) improve soil and water quality, 4) reduce risk to humans and other organisms, 5) utilize natural biological controls, 6) promote crop diversification, and 7) enhance quality of life through increases in net farmer income and other aspects of environmental and economic sustainability.
    4. Project objectives: The hypothesis of this study is that short potato rotations, as compared to longer rotations, result in increased fertilizer, equipment, and pesticide use and reduced soil quality, biodiversity, tuber yield, tuber quality/storability, and net return to the grower. The objectives of this project are to quantify the effects and educate growers concerning the long-term impacts of short vs. long periods of time between potato crops with regard to:
    *nematodes *weed seed bank/numbers
    *wireworm *herbicide-resistance development
    *bacteria:fungi ratios *soil microbial activity
    *Rhizoctonia (Rhizoctonia solani) *soil carbon (OM) and inorganic nutrient conc.
    *silver scurf (Helminthosporium solani) *soil depth, bulk density & aggregate stability
    *white mold (Sclerotinia sclerotiorum) *water infiltration rate
    *pink rot (Phytophthora erythroseptica) *biomass yield
    *Pythium leak (Pythium species) *tuber yield, size, grade, solids, and defects
    *Verticillium wilt (Verticillium dahliae) *net economic return
    *powdery scab (Spongospora subterranea subsp. subterranea) *cost per rotational acre *cost per potato acre and per cwt
    5. Project methods: In cooperation with growers, farm managers, and crop advisors, 36 potato fields will be identified, surveyed and analyzed each year of the three-year study (total of 108 fields). Fields will be selected in pairs, consisting of one field with a short rotation history (1-2 years between potato crops) and the other field with a long rotation history (4+ years between potato crops). An attempt will be made to minimize other differences between the fields in each pair. Ideally, paired fields will be in close proximity to each other and will have similar climate, soil, previous crop, and current season management (variety, tillage, fertilization, pest control, etc.). The 36 fields will be equally distributed among the six primary potato growing regions in the PNW (three pairs/six fields in each region). Regional distribution provides an approximate proportionality with regard to potato acreage distribution in the PNW and includes: 1) Central Washington, 2) Columbia Basin Oregon/Washington, 3) Western Idaho/Eastern Oregon, 4) South Central Idaho, 5) Southeastern Idaho (southern valley), and 6) Southeastern Idaho (northern valley).
    The most challenging aspect of the project will be to identify pairs of fields in close proximity to each other that have a consistent cropping history. In other words, it may be difficult to identify short rotation fields that have a history of potatoes grown in the field at least every other year for a decade or more. It may be even more difficult to identify long rotation fields that have a history of potatoes grown no more frequently than every four years and a minimum of at least once in the field in the previous decade. However, a preliminary consultation with growers and agronomists in each of these regions indicates that identification of fields meeting these criteria is achievable. Historical management data for all fields will be collected from growers, catalogued in a database, and analyzed.
    Field Survey - Pre-season soil samples (30 sub-samples per field) will be taken to a depth of 30 cm (12 in.) from each field and analyzed for organic and inorganic carbon and nitrogen; bicarbonate extractable phosphorus, potassium, and sulfur; DTPA extractable zinc, iron, manganese, copper, and boron. Depth of surface topsoil (A Horizon) will be determined at the same time. Relative soil bulk density readings will be made with a penetrometer. Water infiltration rates will be determined utilizing a permeameter. Soil microbial activity will be determined by incubation and measurement of carbon dioxide evolution. Total and species specific wireworm, nematode, and weed seed counts will be determined by sifting and washing soil samples. Total fungi and bacteria counts will be made by plate counts, and selected fungal pathogens will be quantified.
    Data collection/measurements will be conducted three times during the growing season by working with growers and scouting for the presence of the potato pests previously listed. Weed seeds will be collected from mature plants in random areas within each field during the last scouting event and used in a greenhouse spray study to determine the presence of herbicide-resistant weed populations.
    Five 6 m (20 ft) sections of row will be mechanically harvested from each field. Harvest will occur 5-21 days after the vine kill date, but prior to the main field harvest. Tubers will be separated and weighed into standard USDA size and grade categories. Presence of any external disease symptoms or physiological problems will be quantified. Thirty randomly selected tubers from each field will be scored for internal symptoms of disease of physiological problems. Ten randomly selected tubers will be weighed in air and in water to determine the specific gravity. One hundred randomly selected tubers per field will be examined for wireworm feeding damage. Ten randomly selected dry tubers from each field will be stored for approximately 180 days at an appropriate temperature and humidity (based on variety), after which they will be reexamined for internal and external defects. Tuber sugar concentration and fry color will be determined at harvest and again at the end of the storage period.
    Container Soil Study – Sufficient soil will be collected from each survey field to conduct a container study in a grower’s potato field near Idaho Falls, ID. The soil will be collected each fall prior to when the field survey study is conducted for those particular fields and prior to planned application of fertilizer and/or pesticide applications. This container study complements the field survey by providing an accurate assessment of soil quality and the presence of potato pests in the soil from each survey field under identical climate and management conditions and without confounding effects of varying pesticide applications to the individual fields.
    Although the soil will be containerized, the potatoes in this study will be grown under normal field conditions by burying the containers with top just above the soil surface. Container size will be large (0.08 m3 or 0.1 cubic yards) in order to simulate the volume of soil for normal potato growth. Multiple small holes will be drilled into the side and bottom of each container to allow nearly normal movement of soil water, solutes, and gases. The container will be lined with a mesh mat designed to minimize root penetration into and out of the container. The pots will be arranged in a Randomized Complete Block Design (RCBD) with eight replications. Three seed pieces will be planted in each pot and will be thinned to one plant per pot 45 days after planting to insure similar vigor and stem number in each pot.
    Weekly in-season measurements will be made to determine the presence and impact of weeds and disease pathogens. Each plant will be harvested 5-21 days after the vine kill date, but prior to the main field harvest and quantified for leaf, vine, root, and tuber biomass. Tubers will be separated and weighed into USDA size and grade categories. Tubers will be stored for approximately 180 days at appropriate temperature and humidity levels, after which they will be scored for external and internal defects, specific gravity, sugar concentration, and fry color. The soil will be analyzed after harvest for weed seed, wireworm, nematode, fungi and bacteria counts. Soil suppressiveness will be estimated by replanting tuber seed pieces in the soil, inoculating the system with conidia of Verticillium dahliae, and then determining the incidence and severity of resulting plant wilt (potato early dying).
    Economic and Statistical Analysis – Both the field survey and the container soil study data will be used to modify existing enterprise budgets, or to develop new enterprise budgets as appropriate. These rotation-specific potato enterprise budgets (costs and returns estimates) will be used in a scenario analysis in cooperation with growers and farm managers. If additional funding can be obtained, this analysis will be extended across other typical rotational crops so that rotational budgets can be generated. Enterprise budgets will comply with the American Agricultural Economics Association’s Commodity Costs and Returns Estimation Handbook. Yields in the field survey study will be standardized, based on local averages, for comparison across the region. All measured components of the field survey study will be assessed using means analysis (ANOVA with LSD mean separation) as well as categorical analysis for count data, e.g. log-linear modeling, as deemed appropriate. Additional information regarding the potential associations between the physical attributes (soil characteristics) and biological attributes (yields, pests, pathogens, etc) will be explored using multivariate procedures such as principle components and/or canonical correlation analyses. The potted soil study will be analyzed using ANOVA with LSD mean separation.
    Grower Education – The most important procedures for this project relate to the information dissemination and have already been described thoroughly above in the Outcomes – Impacts: Information Dissemination section (see section 1.b.).

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.