Precipitated Calcium Carbonate to Remediate Acidic Eastern Idaho Soils

Progress report for OW23-382

Project Type: Professional + Producer
Funds awarded in 2023: $75,000.00
Projected End Date: 08/31/2026
Grant Recipient: University of Idaho
Region: Western
State: Idaho
Principal Investigator:
Dr. Jared Spackman
University of Idaho
Jared Gibbons
University of Idaho
Justin Hatch
University of Idaho
Tom Jacobsen
University of Idaho
Joseph Sagers
University of Idaho
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Project Information


Soil acidification negatively impacts the potential yield and quality of agronomic crops, decreases plant available nutrients in the soil, and increases weed and disease pressure. While most arable farmland in eastern Idaho has high pH testing soils, soil acidity is becoming increasingly problematic in eastern Idaho, especially in Fremont, Caribou, Bonneville, and Oneida counties. Precipitated calcium carbonate (PCC), a by-product derived from the sugar beet sugar purification process, is a readily available lime source to remediate acidic soils in eastern Idaho. This project will address the needs of eastern Idaho producers by conducting on-farm, variable PCC rate strip trials and annually monitoring changes in crop yield, weed presence, and soil pH at multiple soil depths over three years. This project will also evaluate the DualEM electrical conductivity sensor to map changes in soil texture across a field and develop variable-rate PCC prescriptions. Education and outreach about soil acidity, its impacts on agriculture, liming materials, and how lime rate prescriptions are made will be done through annual field days; outreach materials including newspaper, TV, and radio stories;  presentations at producer and professional meetings; and Extension bulletins and journal articles. We expect this project to benefit 160,000 acres of acidifying soils in eastern Idaho, and to be of value to producers in northern Idaho and other western states. We anticipate this project to have 400 direct contacts and more than 11,000 indirect contacts annually.

Project Objectives:
  • Conduct on-farm field trials to remediate acidic soils using precipitated calcium carbonate in eastern Idaho (September 2023 – August 2026).
  • Provide agricultural stakeholders with information regarding liming for acidic soil remediation and weed control through direct engagement at field days and workshops and indirect contacts including newspaper articles and Extension bulletins (September 2024 – August 2026).

The first four major milestones associated with Objective 1 is fall soil sampling before (2023) and after (2024, 2025, 2026) applying PCC to each field site. These measurements will provide baseline information about each field and allow us to track changes in soil pH due to PCC applications and field management. Additional milestones for Objective 1 include collecting and analyzing yield data from each georeferenced point within each treatment strip in August for small grains and June and August of 2024, 2025, and 2026 for alfalfa. This data is critical for the study because it will inform us of the economical (dis)advantage gained from applying PCC.

For Objective 2, annual summer field days will be held in July 2024, 2025, and 2026. The field days are prime opportunities to disseminate information about acid soils and PCC as a soil amendment to a diverse audience. Further, the general populace has an opportunity to observe treatment differences and ask questions. One (2023, 2024) or two (2025) Extension bulletins will be developed and published each fall to early winter and distributed at subsequent field days. The final milestone of drafting and publishing one or more journal articles and the project dataset will occur during the summer of 2026.

Spackman WSARE Timeline


Click linked name(s) to expand/collapse or show everyone's info
  • Scott Brown - Producer
  • Brody Harshbarger - Producer
  • Jason Howell - Producer
  • Bryan Miller
  • Taelynn Nelson
  • John O'Connell
  • Ryan Orme - Producer
  • Tom Sharp
  • Dr. Jared Spackman - Technical Advisor (Educator and Researcher)
  • Brent Stohl - Producer


Materials and methods:

Objective 1: Conduct on-farm field trials to remediate acidic soils using precipitated calcium carbonate in eastern Idaho (September 2023 – August 2026)

On-farm field scale strip trials were conducted and maintained in Fremont County (one location) and Caribou County (two locations) from 2023 to 2026 on acidic soils (pH <5.5). Selected field sites have not received lime applications within five years of study initiation and will have a soil surface pH ≤5.6. The typical crop rotation of these regions was small grains (either barley or wheat) rotated with alfalfa. The field sites were tilled (typical of regional management practices) to incorporate the lime because these locations have high elevations (e.g., 5200–6200’ above sea level) with cool, short growing seasons. Selected field sites were planted into small grains during the 2023 growing season to ensure that the lime could be incorporated into the soil with tillage. 

Lime application treatments consisted of four rates of PCC applied at 0, 2, 4, and 6 "as applied" tons per acre with four replications. These rates encompass the lime application rates reported by producers in Fremont County. The individual strips were long (e.g., 450’) and narrow (e.g., 50’) to capture natural variation across the field and to match the width of a commercial applicator’s spreader.

Precipitated calcium carbonate applied to a recently harvested potato field
Precipitated calcium carbonate (gray) was applied to a recently harvested potato field in Ashton, Idaho on October 11, 2021, with a surface soil pH of 5.4. The liming rates were 4, 0, 2, and 6 tons per acre.

To verify the applied PCC lime rate, we placed disposable 9" diameter plates every 112’ along the center of each strip (3 plates per strip). The mass of PCC collected in each pan was divided by the surface area of the plate and converted to tons per acre.  PCC was obtained from Amalgamated Sugar Company and was applied from September to October 2023. Other than liming, the strip trials were managed according to each producer’s individual practices including method and depth of lime incorporation, crop rotation, and harvest timing.   

Soil samples were collected from a 112’ x 50’ georeferenced grid soil sampling pattern (~0.38-acre grid) at 0-2, 2-4, 4-6, and 6-12” depths in September to October of 2023 before liming and will be collected in August–September of 2024, 2025, and 2026. These soil samples were dried, ground, homogenized, and analyzed at the University of Idaho for soil pH1:1 (soil: water) (method S-2.20; Gavlak et al., 2005), electrical conductivity (method S-2.30; Gavlak et al., 2005), and free lime if the soil pH>7. Each fall, additional soil samples will be collected at 0-6” depths and analyzed for extractable aluminum (a source of soil acidity and root toxicity; method S-15.10; Gavlak et al., 2005). In 2024, each site will be characterized for macro- and micronutrient content and soil physical properties (bulk density, soil texture).

We will map the study area for soil electrical conductivity using an EM38 electrical conductivity sensor in 2024. Each pass of the sensor will be spaced 25’ to 30’ to provide a high spatial resolution of changes in soil electrical conductivity. Soil electrical conductivity is well correlated to soil texture. This map, combined with a topography map and our grid-sampled soil pH measurements, was used to explore the feasibility of developing variable-lime-rate maps (Cossel et al., 2019). ArcGIS will be used to map each layer and explore ordinary kriging, inverse distance weighting, and radial base function statistical analyses to interpolate soil pH and electrical conductivity measurements to the rest of the study area (Zandi et al., 2011). If successful, this will allow producers to potentially save money by adjusting their lime rates to match the soil requirements instead of applying a blanket lime application.

Our collaborating producers have noted that certain weeds, such as corn spurry and barnyard grass, thrive in low pH conditions. Due to tillage before liming, we were unable to document (photograph, record weed biomass and/or plant count per square foot, weed species) and georeference regions of the field where significant weed patches (≥100 square feet) were prevalent. However, weed patches will be marked and georeferenced starting in the summer of 2024 and changes in weed pressure, species, and patch sizes will be recorded.

In years when small grain crops will be grown, we will collect the following information from each georeferenced point: stand counts and visual differences in color or development at Feekes 2–3, evidence of root deformity or stunting (evidence of aluminum toxicity), heading date, maturity date, number of kernels per head, and number of stems per plant. Yield will be measured in each plot with a plot combine by harvesting four 5’ by 100’ strips from the center of each strip plot. Yield components (test weight, grain protein) will be evaluated on a grain subsample from each 5’ by 100’ strip. Straw yield will be estimated by collecting 5’ of windrow from the center of each 100’ long strip. Nutrient removal in the grain and straw will be estimated by collecting a representative grain and straw sample from each georeferenced point and analyzing it for macro- and micronutrient content.

To ensure that the data we collected will be available for future research, we utilized the USDA Fertilizer Recommendation Support Tool minimum data set (Slaton et al., 2021) to record information about the field sites, management practices, and data results. At the completion of the study, the data set will be published at Ag Data Commons to allow other researchers access to our raw data.  

Research results and discussion:

In the fall of 2023, Dr. Spackman, Tom Jacobsen, and Jared Gibbons worked with cooperating producers to identify several potential field sites for the new studies. Using a portable pH probe and a GPS, they mapped the surface soil pH of several fields. Five fields were selected that exhibited surface soil pH values <5.6. Three fields were used for this Western SARE project and two fields were utilized for a companion study funded by the Idaho Barley Commission. The fields exhibited significant variation in soil pH, potentially due to water movement, topography, and changes in soil texture. These field sites were selected in hopes that they would prove successful candidates for generating variable lime rate prescription maps. 

Surface soil (0-1") pH map
Soda Springs, Idaho 1. Surface soil (0-1" depth) pH map measured in the fall of 2023 north of Soda Springs, Idaho. Soil pH values ranged from 3.68 (red) to 7.53 (green).
Surface soil (0-1") pH map
Soda Springs, Idaho 2. Surface soil (0-1" depth) pH map measured in the fall of 2023 north of Soda Springs, Idaho. Soil pH values ranged from 3.8 (red) to 7.1 (green).
Surface soil (0-1") pH map
Lamont, Idaho. Surface soil (0-1" depth) pH map measured in the fall of 2023 near Lamont, Idaho. Soil pH values ranged from 5.51 (red) to 5.67 (green).

PCC was shipped to each site from the Amalgamated Sugar beet processing plant in Paul, Idaho. Ten subsamples were collected and composited from each PCC shipment and analyzed for calcium carbonate equivalent, moisture, nutrient content, pH, and salt content (Table 1). On a wet basis, the average calcium carbonate equivalent value was 54% of a pure, dry limestone. Approximately 25% of the material was water. In addition to serving as a lime source, PCC contains some plant nutrients including 25 lb P2O5, 2 lb K2O, 10 lb sulfur, and 16 lb magnesium per ton of "as applied" material.      

Table 1. Measured physical and chemical properties of the precipitated calcium carbonate used at the three field sites in Soda Springs and Lamont, Idaho. 

  Soda Springs 1, Idaho Soda Spring 2, Idaho Lamont, Idaho
Calcium carbonate equivalent %, on an as received basis 54.9 46.9 60.2
Dry matter % 75 64.8 81.8
Dry matter, lb/ton as received basis 1500 1296 1636
Total N, lb/ton as received basis  6 4.8 6.87
Total Carbon, lb/ton as received basis  159 160.06 213.5
C:N Ratio, Dry wt. basis % 26.5:1 33.3:1 31.1:1
Nitrate-N, lb/ton as received basis  0.02 0.03 0.01
P2O5, lb/ton as received basis  25.65 20.61 27.32
K2O, lb/ton as received basis  3.3 1.43 0.33
Calcium, lb/ton as received basis  471.75 407.98 491.13
Magnesium, lb/ton as received basis  16.65 14.26 18.16
Sulfur, lb/ton as received basis  9.9 7.91 10.47
Zinc, lb/ton as received basis  0.056 0.012 0.023
Iron, lb/ton as received basis  2.193 1.818 2.336
Manganese, lb/ton as received basis  0.266 0.226 0.28
Copper, lb/ton as received basis  0.011 0.104 0.005
Boron, lb/ton as received basis  0.011 0.003 0.002
Sodium,lb/ton as received basis  0.96 0.87 1.15
P, lb/ton as received basis  11.3 9.1 12
K, lb/ton as received basis  2.7 1.2 0.3
pH, as received, Dry wt. basis % 8.7 8.9 8.7
Salts as EC, mmhos/cm, Dry wt. basis % 0.7 0.7 2

A total of 576 soil samples were collected in the fall of 2023 from the three field sites. These soil samples have been dried, ground and are currently being analyzed for soil pH (1:1 soil:water) and electrical conductivity. 

Participation Summary
7 Producers participating in research

Research Outcomes

Recommendations for sustainable agricultural production and future research:

There can be significant variation of soil pH values measured across a field and by depth within a soil profile. Previous results from our lab have indicated that the soil pH of eastern Idaho soils increases with depth, indicating that these soils are likely acidifying due to historic agricultural management practices. Fertilizers are typically applied in the top 6" of the soil profile. Ammonia-based and elemental sulfur fertilizers acidify the soil as they are nitrified or mineralized. Soil sampling depth may mask potential acidity issues in a field. Because the deeper subsoils are likely more alkaline than surface soils, collecting soil samples to 1', as is common in southern Idaho, may fail to capture acidic soil issues. When soil acidification is a potential concern it may be advisable to collect soil samples to 6" for more timely remediation of acidity issues. 

When considering liming as an amendment for acidic agricultural fields, it is useful to understand spatial variation across a field. This may be accomplished through grid or zone sampling. This research has indicated that soil pH may vary with topography. For example, the Lamont field site soils were more acidic soils on the toeslope and became increasingly alkaline moving up the hillslope to the hilltop. Soda Springs 1 and Soda Springs 2 tended to have more acidic soils in the rills between hillslopes where surface and subsurface runoff was most likely to leach and remove base cations. 

1 Grant received that built upon this project
1 New working collaborations

Education and Outreach

1 Consultations
3 On-farm demonstrations

Participation Summary:

80 Farmers participated
25 Ag professionals participated
Education and outreach methods and analyses:

We intend to use field days, crop schools, Extension bulletins, journal articles, and newspaper and magazine articles to disseminate educational information about soil acidity, liming, and our project results. To encourage participation at cereal schools, we advertised upcoming events and conferences on the University of Idaho calendar, by emailing growers and crop advisors, posting flyers at local businesses and gathering places, phone calls, and our day-to-day interactions with stakeholders.  

Education and outreach results:

As of March 2024, information from this study has been shared at the 2023 Western Alfalfa and Forage Symposium: Soil Fertility and Health Workshop and two cereal schools held in Soda Springs and St. Anthony, Idaho in February 2024. These presentations directly taught 105 growers, crop advisors, industry representatives, and university Extension educators and researchers. At each of these events, we included images detailing the impact of soil acidity on crop production giving real-world examples of how liming remediated soil acidity and improved crop productivity.

Further, at the time of precipitated calcium carbonate application, we held several detailed discussions with our collaborating producers about the study and the potential effects we expected to observe in the on-farm trials. For the on-farm trials, we specifically picked areas of their fields where the measured soil pH values were low and/or variable. We also shared the soil pH maps and discussed how past management practices (tillage, fertilizer sources, etc) may have contributed to the soil acidity issues they currently face.  

Education and Outreach Outcomes

Recommendations for education and outreach:

It is important to closely coordinate our educational events with other agricultural education suppliers, such as local coops and ag dealers. Several of our cereal schools, while well advertised, were not attended as well as we had hoped because other groups were holding their grower meetings on the same day. For example, Valley Wide held a grower meeting in St Anthony on the same day we held our cereal school. Several growers and Valley Wide crop consultants expressed a desire to attend our cereal school but were obligated to attend the Valley Wide meeting. To remedy this, we have already selected the dates for the 2025 cereal schools and have begun sharing the dates with the local coops and ag dealers so we don't schedule our meetings on top of one another.  

3 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Key changes:
  • Soil pH

  • optimum Soil pH ranges for crops

  • Effect of liming on soil pH

  • Selecting the appropriate lime rate

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.