By Karen Hills
A frequently used—at least, by soil scientists—definition for soil health is “the continued capacity of soil to function as a vital living system […] to sustain biological productivity, maintain the quality of air and water environments, and promote plant, animal, and human health” (Doran et al. 1996). Many different indicators—chemical, physical, and biological—are used to assess soil health.
Growing potatoes is notoriously hard on the physical and biological health of soil (Figure 1). Potato production in many areas of the Pacific Northwest involves seven or more soil disturbance operations, leaves little residue on the field, and often involves the use of fumigants to control soilborne diseases. The economics of potato production often drive growers to utilize short rotations. But a suite of strategies are possible to improve soil health in potato production, including cover crops, rotating with perennial crops and crops that contribute high levels of residues, and incorporation of organic amendments. While growing green manure crops for biofumigation has probably achieved the most success and adoption in the region (see producer Dale Gies as an example), in this article I focus on a more challenging strategy that has received limited attention, but may have more direct climate change implications: tillage reduction.
Tillage reduction in potatoes? Is that really possible?
The short answer is “it’s possible, but it’s not yet clear it’s worth it.” A study examining reduced tillage in a sweet corn-sweet corn-potato rotation in Paterson, Washington found no significant difference in potato yields between the conventional and reduced tillage treatments (Collins et al. 2010), but wind erosion decreased in the reduced tillage plots (Sharratt and Collins, 2018; Figure 2). Returns over total costs for the potato year of the rotation were $2,477 per acre in the reduced tillage system, compared to $2,421 per acre for the conventional tillage system. Over the whole three-year rotation, returns were slightly less for the reduced tillage system ($803 per acre) than for the conventional tillage system ($812 per acre; Painter 2009a, 2009b). The bottom line here is that since yields and returns were similar, substantial co-benefits would be needed to drive adoption.
Carbon Sequestration Potential
Carbon sequestration is a co-benefit of many practices that improve soil health, including tillage reduction. When soil health improves, carbon that would otherwise be released to the atmosphere as carbon dioxide is sequestered in cropland. Irrigated cropping systems (including rotations with potatoes in them) have great potential for contributing to carbon sequestration due to their high productivity (and thus high potential to put carbon into the soil) relative to native sagebrush vegetation or dryland cropping systems. A modeling study found that, over 12 years, tillage reduction resulted in sequestration of 0.08 to 0.15 tons carbon dioxide equivalent (CO2e) per acre per year in an irrigated sweet corn-sweet corn-potato rotation in Paterson, Washington (Stockle et al. 2012).
Another study estimated that, if the irrigated crop area in southern Idaho currently tilled with moldboard plow were converted to conservation tillage, a net gain of 0.52 tons CO2e per acre per year would occur over 30 years (Entry et al. 2002). Expanding this calculation to the whole irrigated area of the Pacific Northwest would result in a gain of 311 million metric tons CO2e or 0.15% of the projected worldwide carbon emissions over the following 30 years (Entry et al. 2002). In the absence of carbon markets that reimburse farmers for carbon sequestration, significant soil benefits from tillage reduction (e.g., improved infiltration and water holding capacity, reduced wind erosion) would need to drive adoption in potato production. So far, this has not happened.
Moving from Oxymoron to Opportunity
There are other barriers to overcome in order to improve soil health through reduced tillage, such as the potential need for new equipment, the lack of understanding of how such a change would affect potato quality and pathogen pressure. In addition, soil organic carbon is not easy to increase in some of the coarser sandy soils where potatoes are grown (e.g., Quincy sand, which is 92% sand), so improvements may come gradually.
Despite these barriers, improving soil health in potato production can be seen as an opportunity—at least in some of the widely varied potato growing areas—given the vast potato acreage in the Pacific Northwest, and the chances to impact soil health through management changes during non-potato years of the rotation. Some combination of the co-benefits of soil health (e.g., preventing wind erosion, improving water holding capacity), the development of active carbon markets, and increased financial support allowing producers to try new strategies—including, but not limited to, tillage reduction—will be critical for turning this opportunity into a reality, while maintaining producer profitability.
Look for an upcoming post on improving soil health in potato systems from the perspective of producers.
Hills, K., H. Collins, G. Yorgey, A. McGuire, and C. Kruger. 2018. Safeguarding Potato Cropping Systems in the Pacific Northwest Through Improved Soil Health. Report prepared for the Washington State Potato Commission. WSU CSANR. 96 pp.
Yorgey, G.G., S.A. Hall, C.E. Kruger, C.O. Stockle, and M. Donnay. 2019. Carbon sequestration potential in cropland soils in the Pacific Northwest: A summary of what we know and what gaps there are. White paper prepared for the Laird Norton Family Foundation. 49 pages.
Collins, H.P., A.K. Alva, and R. Boydston. 2010. Reduced Tillage in an Irrigated Potato Rotation. CSANR Research Report 2010–001. Climate Friendly Farming. http://csanr.wsu.edu/wp-content/uploads/sites/32/2013/02/CSANR2010-001.Ch20.pdf
Entry, J.A., R.E. Sojka, and G.E. Shewmaker. 2002. Management of irrigated agriculture to increase organic carbon storage in soils. Soil Science Society of America Journal 66(6): 1957–1964.
Hills, K., H. Collins, G. Yorgey, A. McGuire, C. Kruger. 2018. Safeguarding Potato Cropping Systems in the Pacific Northwest Through Improved Soil Health. Report prepared for the Washington State Potato Commission. Center for Sustaining Agriculture and Natural Resources, Washington State University. 96 pp
Painter, K. 2009a. 2009 Crop Rotation Budgets for Potatoes and Sweet Corn Irrigated Crop Production in the Columbia Basin, WA Climate Friendly Farming Project: Reduced Tillage.
Painter, K. 2009b. 2009 Crop Rotation Budgets for Potatoes and Sweet Corn Irrigated Crop Production in the Columbia Basin, WA Climate Friendly Farming Project: Conventional Tillage.
Sharratt, B.S., and H.P. Collins. 2018. Wind erosion potential influenced by tillage in an irrigated potato–sweet corn rotation in the Columbia Basin. Agronomy Journal 110(3):842–49. https://dl.sciencesocieties.org/publications/aj/abstracts/110/3/842
Stockle, C., S. Higgins, A. Kemanian, R. Nelson, D. Huggins, J. Marcos, and H. Collins. 2012. Carbon storage and nitrous oxide emissions of cropping systems in eastern Washington: A simulation study. Journal of Soil and Water Conservation 67(5): 365–377.
USDA NASS. 2018. Quickstats.