Soil Health Assessment Methods Farmers perception Soil health card Solvita soil tests Haney soil tests Comprehensive soil health assessment (CASH)
Soil health assessment
1) Farmer perceptions of soil health
Farmers, in particular experienced crop growers, have the ability and skills to estimate the soil health (quality) of local cropland. The
ability is typically gained through years of soil cultivation and crop production experience. Proficient farmers usually divide their cropland
into “good” and “poor” categories based on the soil health; major underlying soil health issues are identified for “poor” cropland; and
rectifying measures are implemented to improve the soil health and crop productivity of “poor” cropland. Farmers estimate the soil health of
cropland by direct sense-based examination: observing the surroundings and watching, feeling, smelling the soil to collect the rough information
of soil color, aroma (e.g., earthy, sweet vs. sour, putrid), structure (e.g., soft, crumbly vs. hard, chunky), surface crusting, compaction,
infiltration, drainage, and ease of tilth. With additional reference to available crop productivity records, a near correct prediction on the
healthiness of the soil can be drawn.
Farmer perceptions of soil health are generally reliable, as confirmed by scientific studies (Guo, 2021).
2) Soil health card methods
A soil health card is a field tool for assessing soil health and identifying the underlying issues. It is usually designed by soil conservation
offices in collaboration with local farmers and agricultural cooperative extension agents to enhance the adaptation. A localized soil health
card lists a number of soil health indicators selected by farmers based on their farming experience and knowledge of the local environment.
These indicators can be assessed in the field without the aid of laboratory instrumentation. Descriptive ratings associated with these
indicators are also provided on the card to guide users to estimate the soil health of agricultural lands.
The Maryland Soil Health Card is illustrated in Figure 1. Seven soil health indicators are displayed on the card: surface cover (with living
plants and crop residues), infiltration, compaction and root growth, OM content, soil structure/aggregation, earthworms and macroinvertebrates, and
soil odor. For each indicator, the descriptive ratings (scorings) of excellent (9-11 points), good (6-8 points), fair (3-5 points), and
poor (0-2 points) are defined. A free 13-min youtube video to demonstrate how to conduct field soil health assessment using the
Maryland soil health card. The health of a cropland soil is excellent, good, fair,
or poor when the total score (sum of the points from the seven individual soil health indicator ratings) falls in the range of 60-77, 40-56,
20-39, and 0-19, respectively (Figure 1).
Soil health card methods have been adopted by international governments to improve the management of soil and land resources. Figure 1. Maryland soil health card showing individual soil health indicators and the associated descriptive
ratings
3) Solvita soil health tests
Solvita soil health tests are a soil test toolkit invented by Woods End Laboratories, Inc. (Mount Vernon, ME, USA) to provide commercial
services of soil health evaluation. The toolkit contains laboratory measurements of soil samples for five health indicator traits: OM content,
water soluble organic carbon (WSOC), aggregate stability, soil basal respiration or Solvita CO2 burst, and Solvita soil labile amino-N (SLAN).
Soil OM content is typically measured by the 500°C loss-on-ignition method, WSOC by 24-hr, room temperature, 1:5 solid/water ratio extraction
and subsequent C analysis, aggregate stability by the wet sieving methods, basal respiration by 24-hr lab incubation of fresh, undisturbed field
soil sample, Sovita CO2 burst by 24-hr lab incubation of re-wetted dry soil sample, and SLAN by 24-hr lab incubation and subsequent NH4-N
analysis. The measurements are then rated relative to the maximal local expectations (score 50 points) to generate a soil health score in the
range of 0–50 points. The average of the five individual indicator ratings indicates the overall soil health, with a score greater than 25
points as “good” (Guo, 2021).
4) Haney soil health test
The Haney test for soil health is a laboratory dual extraction procedure for estimating the overall health of agricultural soils.
The procedure was developed by Dr. Rick Haney, a USDA-ARS (Agricultural Research Service) scientist in 2010. The test has been used by many
soil testing laboratories to make fertilization recommendations for crop growers.
To conduct the Haney test, soil collected from the crop field is air-dried and processed into less than 2 mm particles. Aliquots of the soil are
extracted with deionized water and analyzed for total N, NH4-N, NO3-N, PO4-P, and organic C in the extracts. Another aliquots of the soil are
extracted with citric acid (H3A) and analyzed for extractable total P, organic P, K, Mg, Ca, Na, Zn, Fe, Mn, Cu, S and Al. A soil sample is
further rewetted by capillary action with deionized water at 2:1 solid/water ratio and incubated at room temperature for 24 hr. The CO2
generated during incubation is quantified to calculate the soil CO2 burst. A health score is computed for the soil following the equation:
Soil health score=[CO_2-C]/10+[WEOC]/50+[WEON]/10, where [CO2-C] is soil CO2-C burst in mg kg-1, [WEOC] is soil water extractable organic
carbon content in mg kg-1, and [WEON] is soil water extractable organic nitrogen content in mg kg-1. The score ranges from 0 to 50, with a
value greater than 7 indicating “good” soil health.
5) Comprehensive assessment of soil health (CASH)
Cornell University (Ithaca, NY, USA) developed the intensive laboratory-based CASH protocols
to assess the overall health of agricultural soils from a suite of selected soil physical, chemical, and biological properties and make best
soil management recommendations based on the major soil health issues. Twelve (12) soil health indicators are included in CASH: soil available
water capacity (AWC), surface hardness, subsurface hardness, wet aggregate stability, soil organic matter (OM) content, active C, soil
respiration, protein index, soil pH, extractable P, extractable potassium (K), and extractable minor nutrients. To follow the CASH protocols,
a composite soil sample (1–2 L in volume or 1.5–3.0 kg in dry weight) representing a management unit (a farmland area) is collected following
appropriate sampling patterns and early delivered to the laboratory. The sample is analyzed for the 12 soil health indicators following the CASH
protocols. The results are then scored by comparing with the established scoring curves. The sum of the 12 individual indicator scores is the
overall soil health score, indicating “very low,” “low,” “medium,” “high,” and “very high,” respectively, in the ranges of 0–20, 20–40, 40–60,
60–80, and 80–100.
A standard CASH report is shown in Figure 2. The analytical results of the soil texture is presented, following by the results and the according
rating score of the 12 health indicators. Different colors are used to denote the individual soil health ratings, with red, orange, yellow,
light green, and dark green indicating very low, low, medium, high, and very high, respectively. Figure 2. A comprehensive soil health assessment report example illustrating the assessment score, overall
health, and main constraints of a cropland soil
Similar soil health assessment systems such as Soil Management and Assessment Framework (SMAF) and Soil Health Assessment Protocol and Evluation
(SHAPE) also exist (Guo, 2021).
Guo, M. 2021. Soil health assessment and management: recent development in science and practices. Soil Syst.
5, 61. doi: 10.3390/soilsystems5040061
Farmers perception
