Precipitated Calcium Carbonate to Remediate Acidic Eastern Idaho Soils

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.

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 pH_1:1 (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.