Details of the testing procedures for the individual soil analyses can be found in the Soil Health Assessment section of the Comprehensive Assessment of Soil Health – The Cornell Framework Manual, or in our Cornell Soil Health Lab Manual Fact Sheet Series.
Individual Soil Analyses:
- pH, Organic Matter Percentage, and Nutrient Testing ($30): A traditional soil fertility test analysis designed for application in the Northeastern U.S. is used to determine soil pH and estimate plant nutrient availability. Results are interpreted within a general framework to evaluate deficiencies or excesses, but are not crop specific. Soil pH is measured using the Cornell pH Test; macro- and micro-nutrients are determined using Modified Morgan Extractions. Organic Matter percentage determined by Loss on Ignition. See factsheets: Standard Nutrient Analysis and Organic Matter.
- Wet Aggregate Stability ($30): Wet aggregate stability is a measure of the extent to which soil aggregates resist falling apart (i.e., slaking) when wetted and exposed to the force of rain drops. This physical soil property is measured using the Cornell Sprinkle Infiltrometer, which steadily rains on a sieve containing a known weight of soil aggregates between 0.25-2.0 mm for five minutes. Unstable aggregates slake and pass through the sieve, while the fraction of soil remaining on the sieve is used to calculate the percent wet aggregate stability. Soils with high wet aggregate stability are more resistant to water and wind erosion and show better overall soil health (e.g., infiltration, root growth, biological activity, etc.). See factsheet: Aggregate Stability.
- Active Carbon ($30): Active Carbon measures the portion of soil organic matter that can serve as a readily available food and energy source for the soil microbial community, thus helping to maintain a healthy soil food web. To measure Active Carbon, soil is reacted with a potassium permanganate solution which has a deep purple color. As the solution oxidizes Active Carbon, it loses some of its color. This loss of color upon reaction is directly proportional to the amount of Active Carbon in the soil sample, which is determined by using a spectrophotometer and calibrated against standards of known concentration. See factsheet: Active Carbon.
- Total Carbon and Total Nitrogen ($30): The Total Carbon (Tot C) analysis measures all of the carbon in a sample using complete oxidation of carbon to CO2 using high temperature combustion (1100°C). When soils have no carbonate minerals, Tot C is equivalent to the soil organic carbon (SOC). However, in soils containing high levels of carbonates (minerals and lime), a significant portion of Tot C may be in the inorganic form. The soil inorganic carbon (SIC) is measured using an additional pressure calcimeter methodology on samples with a pH above 6.5. The measured SIC is subtracted from the Tot C and soil organic carbon (SOC) is reported. The Total Nitrogen includes the organic (living and non-living) and inorganic (or mineral) forms of nitrogen ammonium (NH4+) and nitrate (NO3-) found in soil. The Total Nitrogen is determined following the DUMAS combustion methodology. See factsheet: Total Carbon, Total Nitrogen.
- Surface and Sub-Surface Hardness: Surface and sub-surface hardness are indicators of the soil’s compaction status, which decreases water, air, solute, and root movement through the soil while potentially increasing the likelihood of surface runoff and soil erosion. Surface and sub-surface hardness are both measured as penetration resistance in pounds per square inch (psi) using a field penetrometer or soil compaction tester at two depth increments (surface: 0-6”, subsurface: 6-18”). The Cornell Soil Health Lab can provide clients with a soil penetrometer by mail to collect hardness ratings in the field; these data can then be included for the interpretation of overall Soil Health score. See factsheet: Surface and Subsurface Hardness.
- Rapid Texture ($30): The non-organic, solid material in soils is composed of a mixture of mineral particle sizes, the relative amounts of which determine a soil’s texture. Textural class affects many of the important physical, biological, and chemical processes in the soil, but is not easily altered by management practices because it changes little over time. Although soil texture itself is not a soil health indicator per se, knowledge of the textural class informs the interpretation of soil health indicators. The Rapid Texture procedure involves dispersion of soil particles using sodium hexametaphosphate followed by the 1) isolation of the sand fraction using a 0.053 mm sieve, and 2) separation of the silt and clay fractions by settling. See factsheet: Soil Texture.
- Soil Respiration ($30): Soil respiration is a measure of the metabolic activity of soil microorganisms. Respiration is determined by capturing and quantifying the amount of carbon dioxide (CO2) released from a re-wetted sample of dried, 8 mm sieved soil stored at room temperature in an airtight jar for four days. Greater release of CO2 is indicative of a larger, more active soil microbial community participating in carbon mineralization and OM decomposition. See factsheet: Respiration.
- Predicted Available Water Capacity: Beginning in 2019, the Cornell Soil Health Lab moved to predict Available Water Capacity (AWC) using a random forest model, from a suite of measured sample parameters in the Standard Comprehensive Assessment of Soil Health (CASH) package. See factsheet Predicted Available Water Capacity for a detailed explanation of the AWC prediction process. The laboratory measured AWC will remain available as an optional add-on to the CASH packages. Note: This test is not available as an individual soil analysis.
- Predicted Autoclave-Citrate Extractable (ACE) Protein Test: The Autoclave-Citrate Extractable (ACE) Protein Index is used as an indicator of the fraction of the soil organic matter pool that is present as proteins or protein-like substances. Soil protein content is an indicator of the biological and chemical quality of the soil, and is very well associated with the overall soil health status because it represents the largest pool of organically-bound nitrogen in the soil. Soil proteins are determined using a sodium citrate extraction under autoclaving (high temperature and pressure); extracted proteins are quantified using the colorimetric bicinchoninic acid assay (BCA) as calibrated against protein standards of known concentration. See factsheets: Soil Protein and Predicted Protein.
- Autoclave-Citrate Extractable (ACE) Protein Test ($30): The Autoclave-Citrate Extractable (ACE) Protein Index is used as an indicator of the fraction of the soil organic matter pool that is present as proteins or protein-like substances. Soil protein content is an indicator of the biological and chemical quality of the soil, and is very well associated with the overall soil health status because it represents the largest pool of organically-bound nitrogen in the soil. Soil proteins are determined using a sodium citrate extraction under autoclaving (high temperature and pressure); extracted proteins are quantified using the colorimetric bicinchoninic acid assay (BCA) as calibrated against protein standards of known concentration. See factsheets: Soil Protein and Predicted Protein.
- Available Water Capacity ($30): Available water capacity is the amount of plant available water the soil can store. In the field, a soil is at the upper end of soil wetness when water that it cannot hold against the force of gravity has drained – this is called ‘field capacity.’ The lower end of the range is referred to as the ‘permanent wilting point,’ which occurs when only hygroscopic water remains (i.e., water tightly held so tightly onto soil particle surfaces that it is inaccessible by plant roots). Available water capacity is determined from measuring the soil’s water content at both field capacity and permanent wilting point in the lab and calculating the difference. Note: New for 2019. This soil analysis has been replaced by Predicted Available Water Capacity in the Standard and Extended packages and is only available as an add-on test. See factsheet: Available Water Capacity.
- Soluble Salts ($15): Soils become saline when the concentration of soluble salts in the soil profile become excessive. Problems with salts may occur naturally but are especially prevalent in high tunnels and greenhouses as well as under irrigated agriculture in semi-arid and arid areas where water from rainfall would not other wise be adequate for crop production. Soluble salts are extracted from the soil in a 1:1 soil water suspension by volume and measured using a calibrated conductivity meter. See factsheet: Soluble Salts
- Bulk Density and Stone Content ($30): Soil density and stone content are useful parameters for soil classification and in soil health assessments. Samples can be taken within a field to compare soil density and compaction between locations (or depths) in the field. Soil Bulk Density (BD) is a measure of the weight of dry material contained in a sampled volume of soil. Each BD sample is obtained by a collecting a cylinder of known soil volume through the depth of interest. This material can be removed from the cylinder in the field and placed into a bag. Sampling accuracy is increased by compositing multiple cylinders into each sample bag. Soil material and stones (>2 mm) are dried separately in the lab. Data are reported on a with stone (As Sampled) and a without stone basis. The units used are grams of dry soil per cubic centimeter soil volume. Bulk Density information is useful for converting percent carbon laboratory data to the weight of carbon across an area of land and the depth interval measured. See factsheet: Bulk Density. NOTE: Please contact lab for sampling instructions before sampling for Bulk Density.
- Heavy Metals ($80): Heavy metals in soil can adversely affect plant growth as well as human health, depending on the levels of contamination. Soils can be contaminated by numerous human activities, and because heavy metals can persist in soil, the contamination does not need to be recent. We use EPA 3050 digestion analysis and report levels of Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), Nickel (Ni), and Zinc (Zn) in parts per million (ppm). See Soil Heavy Metal Testing for more information.