Soil Health

 Soil health is defined as “the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health” (Doran and Parkin, 1994).  Healthy soils are characterized by high levels of organic matter, better water-holding capacity and drainage, adequate supply of nutrients, sufficient depth for root growth, large and diverse populations of beneficial micro-organisms, and low populations of pathogens and pests. These characteristics lead to improved nutrient cycling, higher yield, and quality. Knowing how soil health influences wheat production, and how growing wheat affects the soil health parameters would help growers improve their nutrient management. Nutrient management would benefit short- term (current wheat production year) and long-term (future crops in the rotation).

Soil health slides from uiolgawalsh

 The Soil Health test is an integrated approach to soil testing using chemical and biological data. Soil Organic Matter is considered a critical Tier 1 indicator of soil health (Soil Health Institute, 2018). Here is an example of soil Organic Matter depletion due to intensive agricultural activities in Idaho. The test is designed to mimic nature’s approach to soil nutrient availability as closely as it is possible in a laboratory. The test uses nature’s biology and chemistry by using a soil microbial activity indicator, a soil water extract (nature’s solvent), and the organic acid extractant H3A, which mimics the production of organic acids by living plant roots to temporarily change the pH in the area around the roots thereby increasing nutrient availability. This integrated approach to soil testing reflects the complex ecosystem of soil, instead of depending on the narrow measurement of inorganic N, P, and K. This enables to obtain realistic measurements of nutrient levels that not exceed what is actually available from the organic N and P pools. This test is designed to answer important questions about the soil: 1) What is the soil’s condition? 2) Is the soil in balance? 3) What can be done to improve the soil.

We are currently conducting the Soil Health sampling/testing for hard red, soft white, and hard white wheat (spring and winter) at Parma, Aberdeen, and Kimberly. This work will add tremendous value to other information we will obtain with the USDA-NIFA funded project. The information will be used to 1) establish a Soil Health database for Idaho cropping systems, and 2) update nutrient management guidelines for wheat.

Soil Health and Fertility Test
Analysis	Importance
Respiration (Infrared Gas Analyzer)	CO2-C in ppm released in 24 hrs by soil microbes after soil has been dried and rewetted. Measure of microbial activity in the soil and is highly related to soil fertility.
Extractable Organic Carbon	Amount of organic C in ppm extracted from the soil with water. Reflects the energy/food source available to soil microbes.
Extractable Organic N	Total water extractable N expressed in ppm.
Total Available N	The total amount of plant available N in your soil expressed in pounds of N per acre.
Available Inorganic N	The amount of ammonium and nitrate N in pounds of N per acre.
Available Organic N	The amount of N being released through mineralization (Nmin) in pounds of N per acre. Estimates how much N is immediately available to plants. The amount of Nmin depends on the organic C: N value.
Extra N Credited for Active/Healthy Soils	Included in the organic N release when >0. Used to adjust the potential organic N release. Soils that are “healthier” are more efficient at mineralizing N.
% Microbially Active Carbon	Percent of water extractable organic C that the soil microbes broke down is 24 hrs. It is the Infrared Gas Analyzer CO2-C divided by the organic C times 100. Should be above 20.
Organic C: N	Ratio of water extracted organic C to organic N. Used to estimate potential N and P mineralization. Indicator of soil health has a significant impact on the activity of soil microbes.  Should be below 20.
Organic N:P	Ratio of organic N to organic P. Should be ≤ 5. A higher number indicates a soil system that may be out of balance and needs adjustment.
Total Available P	Total plant available P in lbs P2O5 per acre.
Available Inorganic P	Inorganic P extracted with H3A and analyzed for orthophosphate in pounds of P2O5 per acre.
Available Organic P	Amount of P that will be released through mineralization of organic P by soil microbes depending on their activity and the organic C:N ratio in pounds of P2O5 per acre.
% P Saturation Iron + Aluminum	Amount of soil P divided by the amount of Fe and Al. Values below 5 typically indicate the need for P fertilizer.
% P Saturation Calcium	Amount of P divided by the amount of Ca. Values below 5 typically indicate the need for P fertilizer.
K2O lbs per acre	Pounds of plant available K2O per acre.
Calcium + Magnesium / Aluminum	In conjunction with the Ca:Mg ratio can be used to determine if an application of lime or gypsum is needed.
Calcium: Magnesium ratio	Balanced soil has Ca: Mg values between 5 and 8.
Soil Health Index	Calculated as 1-day CO2-C divided by organic C:N ratio plus a weighted organic carbon and organic N addition. Represents the overall health of your soil. Ideally, should be above 7.

The Soil Health Index value of 7 may never be achievable for some soils (i.e. sandy soils), while for other soils it may be much greater than 7. Taking a sample from an undisturbed or native soil can help to gauge what this value should be for a particular grower’s field. In addition, keeping track of the Soil Health Index will allow to assess the effects of management practices over the years.

Building a Soil Health database will be helpful for prescribing the appropriate targets for Idaho cropping systems. An additional feature of the proposed Soil Health test is a recommendation for a Cover Crop Mix -   Suggested cover crop mix recommendations are based on soil test data, the soil health score, and the organic C:N ratio. The recommendations are designed to provide soil with a mixed species cover crop to help improve and sustain soil health for a specific field.

By gathering in-depth local information on Soil Health status of farmed fields over several years, this project will help growers to stay ahead of the game in anticipation of the forthcoming guidelines and regulations associated with nutrient management and fertilizer applications on Idaho farms that may be put in place by the NRCS and USDA in the future. It is important to note that the Soil Health concept is applicable to all cropping systems (dryland vs irrigated, short vs long rotations) and all crops, including wheat, barley, potatoes, sugar beets. The funding provided by the Idaho wheat growers and the Idaho Wheat Commission is leveraging the current Federal grant support by covering the cost of soil health sampling in our wheat trials along the Snake River Plain. By adding testing of fields planted to other crops in the future will provide a comprehensive picture of the Soil Health status of the Idaho fields.

Helpful resources:

Learn more about Soil Health topics with University of Idaho Extension through virtual field days. In collaboration with Natural Resources Conservation Service.

Soil Health | NRCS - USDA

Soil Health Videos