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North American Project to Evaluate Soil Health Measurements

North American Project to Evaluate Soil Health Measurements

The Soil Health Institute announces methods for evaluating soil health indicators at a continental scale

The concept of soil health is gaining widespread attention because it promotes agricultural practices that are not only good for the farmer and rancher, but also good for the environment.

An abundance of research shows that improving soil health:

  • boosts crop yield,
  • enhances water quality,
  • increases drought resilience,
  • reduces greenhouse gas emissions,
  • increases carbon sequestration,
  • provides pollinator habitat, and
  • builds disease suppression.

However, lack of widely-applicable measurements and methods for assessing soil health are significant barriers to adopting soil health practices and systems.

To address this need, the Soil Health Institute (SHI), in collaboration with the Soil Health Partnership (SHP) and The Nature Conservancy (TNC), received a $9.4 million grant from the Foundation for Food and Agriculture Research (FFAR) to match a similar amount provided by other donors to advance soil health science and implement soil health management practices. A full press release for the project can be found here.

A major goal for the project is to assess the ability of soil health indicators to detect differences in properties of soils that have been managed in different ways for at least 10 years. Thus, it became necessary to identify the particular analytical method for each indicator being evaluated in the project. The Institute convened a “blue ribbon panel” of experts from the United States Department of Agriculture (USDA), several universities, and the private sector (see list of experts below) to develop consensus on how each indicator should be measured. This was achieved for 19 “Tier 1” and 12 “Tier 2” soil health indicators, as provided in Tables 1 and 2, respectively.

A Tier 1 indicator:

  • Is widely considered an effective indicator of soil health;
  • Is defined regionally and by soil groupings across the nation;
  • Has thresholds known to indicate (at minimum) “poor”, “adequate”, and “good” that are outcome-based (crop yield, environmental goals, etc.); and
  • Is responsive to specific management strategies that can be recommended to improve soil functioning.

A Tier 2 indicator needs additional research before users can have the same level of confidence in its measurement, use, and interpretation.

In addition to these specific indicators, the Soil Health Institute will also evaluate three soil health evaluation frameworks; namely, the Soil Health Management Assessment Framework (Andrews et al., 2004), Cornell’s Comprehensive Assessment of Soil Health (Moebius-Clune et al., 2016), and the “Haney test” (Haney et al., 2010).

SHI encourages individuals and organizations who are engaged in long-term (minimum 10-year) agricultural field experiments in the U.S., Canada and Mexico and interested in participating to visit the SHI website here and submit an application to participate in the project by May 31, 2018.

By project conclusion in 2020, the Soil Health Institute expects to have the data required for recommending scientifically-sound soil health indicators to help farmers, scientists, ag policy makers, and others answer the fundamental question: Just how healthy are our soils?

TABLE 1. Tier 1 Soil Health Indicators and Methods to be Assessed

Indicator

Method

Reference

Soil pH 1:2 soil:water, standard pH electrode system Thomas, 1996
Soil Electrical Conductivity (EC) 1:2 soil:water, standard electrical conductivity meter system Rhoades, 1996
Cation Exchange Capacity (CEC) Sum of cations extracted with Mehlich 3 extractant Sikora and Moore, 2014
% Base Saturation (BS) Calculated from cations extracted with Mehlich 3 extractant Sikora and Moore, 2014
Extractable Phosphorus Soil pH >7.2: use Olsen or AB-DTPA extractant; Soil pH< 7.2: use Mehlich 3 extractant Olsen and Sommers, 1982

Soltanpour and Schwab, 1977

Sikora and Moore, 2014

Extractable Potassium Mehlich 3 extractant Sikora and Moore, 2014
Extractable Calcium, Magnesium, Sulfur, Iron, Zinc, Manganese, Copper, and Sodium Mehlich 3 extractant and DTPA derivatives Sikora and Moore, 2014

Lindsay and Norvell, 1978

Total Nitrogen Dry Combustion Nelson and Sommers, 1996
Soil Organic Carbon (SOC) Dry combustion; soil pH > 7.2 treated with acid to eliminate carbon contained in calcium carbonate Nelson and Sommers, 1996
Soil Texture Pipette Method with a minimum of 3 size classes.  Weight/volume measurements Gee and Bauder, 1986
Aggregate Stability Wet sieve procedure. Weight measurement Kemper and Roseneau, 1986
Available Water Holding Capacity Ceramic plate method measured at -33 kPa (-10 kPa for sandy soils) and -1500 kPa Klute, 1986
Bulk Density (BD) Core method: diameter to be determined, (most likely 2-inch or 5.08 cm) Blake and Hartge, 1986
Erosion Rating USDA model(s) (RUSLE2, WEPP, WEPS) appropriate for site USDA Agricultural Research Service
Soil Penetration Resistance Commercial soil penetrometer Lowery and Morrison, 2002
Water Infiltration Rate Double ring Infiltrometer Reynolds, et al., 2012
Crop Yield Obtained from historical and current plot yield data provided by site manager
Short-Term Carbon Mineralization 4-day incubation followed by CO2-C evolution and capture at 50% water-filled pore space. Zibilske, 1994
Nitrogen Mineralization Rate Short-term anaerobic incubation with ammonium and nitrate measured colorimetrically pre- and post-incubation Bundy and Meisinger, 1994

 

TABLE 2. Tier 2 Soil Health Indicators and Methods to be Assessed

Indicator

Method

Reference

Sodium Adsorption Ratio (SAR) Saturated paste extract followed by atomic absorption or inductively coupled plasma spectroscopy Miller, et al., 2013
Soil Stability Index Combination of wet and dry sieving at multiple sieve sizes Franzluebbers, et al., 2000
Active Carbon Permanganate oxidizable carbon (POXC). Digestion followed by colorimetric measurement Weil, et al., 2003
Soil Protein Index Autoclaved Citrate Extractable Schindelbeck, 2016
B-Glucosidase Assay incubation followed by colorimetric measurement Tabatabai, et al., 1994
B-Glucosaminidase Assay incubation followed by colorimetric measurement Deng and Popova, 2011
Phosphatase Assay incubation followed by colorimetric measurement Acosta-Martinez and Tabatabai, 2011
Arylsulfatase Assay incubation followed by colorimetric measurement Klose, et al., 2011
Phospholipid Fatty Acid (PLFA) Bligh-Dyer extractant, solid phase extraction, transesterification; gas chromatography Buyer and Sasser, 2012
Ester-Linked Fatty Acid Methyl Ester (EL-FAME) Mild alkaline methanolysis extraction; gas chromatography Schutter and Dick, 2000
Genomics 18S, 16S or ITS analysis or a combination of 16S and 18S/ITS Thompson, et al., 2017
Reflectance Diffuse reflectance spectroscopy Veum, et al., 2015

This project is made possible through the generous support of General Mills, the Foundation for Food and Agriculture Research, and The Samuel Roberts Noble Foundation.

SHI thanks the following for their input in deliberations on soil health indicator analytical methods:
Veronica Acosta-Martinez – USDA Agricultural Research Service
Alan Franzluebbers – USDA Agricultural Research Service
Doug Karlen – USDA Agricultural Research Service
David Knaebel – USDA Agricultural Research Service
Dan Manter – USDA Agricultural Research Service
Jennifer Moore-Kucera – USDA Natural Resources Conservation Service
David Myrold – Oregon State University
Bob Schindelbeck – Cornell University
Kristen Veum – USDA Agricultural Research Service
Fred Vocasek – ServiTech Labs
For SHI: Sean Bloszies, Wayne Honeycutt, Sheldon Jones, Byron Rath, Steven Shafer, and Paul Tracy

References:
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Andrews, S.S., D.L. Karlen, and C.A. Cambardella. 2004. The soil management assessment framework: A quantitative soil quality evaluation method. Soil Sci. Soc. Am. J. 68:1945-1962.
Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 363-382. In A. Klute (ed.) Methods of soil analysis: Part 1. Physical and mineralogical methods. 2nd ed. Monogr. 9. ASA and SSSA, Madison, WI.
Bundy, L.G., and J.J. Meisinger. 1994. Nitrogen availability indices. p. 951–984. In R.W. Weaver et al. (ed.) Methods of soil analysis: Biochemical and microbial properties. SSSA Monogr. 5. SSSA, Madison, WI.
Buyer, J.S., and M. Sasser. 2012. High throughput phospholipid fatty acid analysis of soils. Appl. Soil Ecol. 61:127-130.
Deng, S., and I. Popova. 2011. Carbohydrate hydrolases. p. 185-209. In R.P. Dick (ed.) Methods of soil enzymology. Soil Sci. Soc. of Am., Madison, WI.
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