Longer potato rotations linked to improved tuber quality and stronger short-term returns in US trials

New research from a multi-state soil health project found that extending potato rotations was associated with quality and economic benefits, while results for fumigation, mustard biofumigation and manure were less consistent.

By Lukie Pieterse, Editor/Publisher of Potato News Today

For potato growers weighing soil health against short-term commercial pressure, newly published US research offers a finding worth examining carefully: growing potatoes less frequently in a rotation was associated with improved tuber quality and better economic results during a four-year, multi-location study.

The latest paper, published online in the American Journal of Potato Research on July 29, 2026, examined disease prevalence and other quality characteristics under four management approaches: longer potato rotations, conventional soil fumigation, mustard biofumigation and manure application.

Using trial data from four locations in the US Midwest and Pacific Northwest, the researchers found that extending the interval between potato crops was associated with quality benefits that could contribute to improved financial returns.

Equally important, the researchers reported that they generally found no evidence that any of the four practices examined caused a decline in tuber quality.

The study does not establish that one practice will deliver the same result on every farm. Nor does it settle the wider debate about the economics of soil health management. It does, however, add field-derived evidence to an increasingly practical question: can growers protect soil and crop health without sacrificing the quality characteristics on which potato prices often depend?

Four practices examined across contrasting regions

The new quality study was led by Kate Binzen Fuller of the US Department of Agriculture’s Economic Research Service and involved researchers associated with the University of Idaho, University of Minnesota, North Dakota State University, Oregon State University, University of Oregon, University of Maine and other research organisations.

The work formed part of the Potato Soil Health Project, a coordinated research initiative funded through the USDA Specialty Crop Research Initiative.

The broader project conducted trials from 2019 through 2022 at seven field sites in Minnesota, Colorado, Wisconsin, Oregon, Idaho and Maine. Because soils, climates, varieties and commercial practices differ substantially among potato-producing regions, researchers designed treatments suited to conditions at each location rather than imposing one identical system everywhere.

For the published quality and economic analyses, usable datasets were available from four locations representing Idaho, Minnesota, North Dakota and Oregon.

The management practices assessed were:

Two-year compared with three-year potato rotations
Conventional soil fumigation
Mustard grown and incorporated as a biofumigant
Animal manure or other organic amendment applications

A two-year rotation in the study generally meant potatoes were grown once every two years. A three-year rotation inserted an additional non-potato crop, so potatoes were grown once every three years.

The rotations were organised to allow researchers to compare two potato-production years during the four-year project.

Quality matters beyond total yield

Potato production is often discussed in terms of yield, but harvested tonnage alone does not determine the value of a crop.

Tuber size distribution, marketable yield, grade and the presence of diseases or other defects can influence what a grower is paid and whether potatoes meet fresh-market or processing specifications. A treatment that raises total yield but produces more unmarketable tubers may provide little financial advantage.

The 2026 study therefore examined disease-related and other quality differences among treatments. Researchers used pairwise comparisons, grouped analyses and regression methods to investigate whether the four soil health-related practices were associated with changes in potato quality.

Their principal conclusion was that longer rotations were associated with quality improvements that could contribute to higher returns. The authors also found no general evidence that fumigation, mustard biofumigation, manure application or longer rotations reduced tuber quality.

That finding should be interpreted carefully. An absence of statistically consistent evidence of harm does not prove that every practice will be neutral or beneficial under all conditions. The effects of manure, biofumigant crops and fumigation can depend on soil type, disease pressure, application method, weather, rotation history and variety.

Companion analysis found an economic advantage

The quality findings reinforce an economic analysis published by members of the same research group in 2025.

That earlier peer-reviewed study used four years of field-trial results and regionally tailored production-cost estimates to compare revenue and profitability under the same general categories of soil health management.

The researchers combined crop yield and quality data with production costs and price information from USDA sources. Their analysis found that three-year potato rotations were consistently associated with better short-term economic outcomes than two-year rotations in the available dataset.

Longer rotations were positively correlated with both revenue and profit across several statistical tests and regression specifications, although results varied among locations.

The analysis did not find consistent differences in revenue or profit associated with conventional fumigation, mustard biofumigation or animal manure applications.

That does not mean those practices had no value. Rather, the researchers could not identify a clear and consistent economic effect across the sites and treatments included in the four-year study.

The distinction is important. A practice may control a particular soilborne pathogen, improve an individual soil property or benefit a specific field without producing a uniform financial response across several regions.

The rotation trade-off has not disappeared

Longer rotations present growers with a fundamental economic tension.

Potatoes are generally a higher-value crop than wheat, corn and many other crops used during rotation years. Growing potatoes once every three years rather than once every two years reduces the frequency with which the farm earns potato-year revenue from the same land.

The researchers explicitly acknowledged this constraint. Although three-year rotations performed better in the study’s potato years, at least part of that advantage may be offset over longer periods by having fewer potato crops in the overall sequence.

The four-year trial was not long enough to determine the complete economic result over several repeated rotations. Soil health effects may accumulate gradually, while crop prices, input costs, disease pressure and land arrangements can change substantially over time.

The research therefore does not offer a universal prescription that three-year rotations will always be more profitable than two-year rotations.

Instead, it suggests that the comparison cannot be reduced to the income forgone in an additional non-potato year. If a longer rotation produces healthier, higher-quality or more marketable potato crops when potatoes return to the field, some of the apparent opportunity cost may be recovered.

Why rotation may influence potato performance

Short potato rotations can allow soilborne pathogens and other production constraints to accumulate, particularly when susceptible varieties are grown repeatedly.

Adding another non-host or less-susceptible crop can interrupt parts of a pathogen’s life cycle and provide more time between potato crops. Rotational crops may also alter crop residues, rooting patterns, nutrient cycling and soil biological communities.

However, rotation is not a complete disease-control measure. Some potato pathogens survive for long periods in soil or have alternative hosts. The effect of a rotation also depends on which crops are included—not simply on the number of years between potato crops.

Researchers and growers must therefore distinguish between rotation length and rotation design. A poorly selected three-year sequence will not necessarily outperform a carefully planned two-year system under every set of conditions.

Why the other practices produced mixed results

The lack of consistent economic findings for manure, mustard biofumigation and fumigation reflects the complexity of evaluating soil management across different potato regions.

Manure can add nutrients and organic matter, but its composition, transport costs and application rates vary. Its influence on disease can also differ among pathogens and soils.

Mustard biofumigation relies on biologically active compounds released when suitable mustard material is incorporated into the soil. Outcomes can depend on mustard species, biomass production, crop growth, incorporation timing, soil moisture and the organisms being targeted.

Conventional fumigation can reduce populations of certain soilborne pathogens and weeds, but it is costly and does not affect every organism equally. Its economic value is likely to be greatest where the target problem is sufficiently severe to justify the treatment.

Pooling results across sites can help identify broad patterns, but it may obscure locally important responses. A practice that performs strongly under one disease complex or soil type may have little measurable effect elsewhere.

Important limitations

Several limitations prevent the findings from being treated as a ready-made recommendation for individual farms.

The trials ran for four years. The researchers noted that soil health changes may take longer to become fully evident.

Treatments were also adapted to regional conditions rather than being identical at every site. That makes the work commercially relevant, but it complicates direct comparisons across locations.

The economic study did not have a uniform baseline treatment shared across every site. Researchers also lacked complete information about how all fields had been managed before the trials began.

Potato varieties differed among locations and included Russet Burbank, Russet Norkotah and, in a smaller number of treatments, Bannock Russet. Varietal resistance and quality characteristics can influence responses to soilborne disease and management practices.

Most importantly, the studies report associations within the experimental dataset. They do not prove that changing rotation length alone caused every observed difference.

A stronger basis for farm-level calculation

The practical value of this research lies less in declaring a single winning practice than in improving the questions growers can ask.

For an individual operation, the value of a longer rotation will depend on:

The diseases and other constraints present in particular fields
The market value of potato quality improvements
Returns available from rotation crops
Land availability and rental costs
Variety susceptibility
Fumigation and amendment costs
The grower’s ability to maintain potato volume while reducing field frequency
Benefits that emerge only over several rotations

In regions where potato acreage is limited and contracts reward annual volume, extending rotations may be commercially difficult even if the agronomic argument is strong. Growers may require access to more land, better markets for rotation crops or incentives that recognise longer-term soil benefits.

That human and economic reality cannot be separated from the science. Growers rarely reject soil health in principle; they operate within contracts, debt obligations, land constraints and narrow seasonal margins.

The latest research does not remove those pressures. It does provide evidence that a longer interval between potato crops need not be viewed merely as lost production time. Under the conditions studied, longer rotations were associated with better tuber quality and stronger short-term economic outcomes.

The unanswered question is whether those gains remain sufficient when measured across repeated rotations and complete farm businesses. Resolving that will require longer trials, more consistent treatment designs and economic analysis extending beyond individual potato years.

For now, the most defensible conclusion is also the most useful: longer rotations showed promise, but their value must be calculated field by field and over years—not assumed from a single season.