Carbon dioxide is naturally released from soils due to microbial processes. At the same time carbon is being absorbed in soils by the humification process. The relationship of these two factors is an important indicator of soil fertility. Declining rates of CO2 respiration are associated with destructive soil practices that are not maintaining the humus content of the soil, and as microbes have less and less food, their mass declines, the overall CO2 rate declines, and many soil qualities deteriorate.
Being able to evaluate the turnover of organic matter via CO2 respiration is important for a number of reasons. The rate of CO2 release is generally regarded as an indicator of soil health and is favorably improved with practices that include cover cropping. The rate of carbon exchange may be used to estimate potential release of nutrients, such as nitrogen and phosphorus, that are constituents of humus. CO2 release also forms the basis for a new agricultural soil test, called the USDA Soil Health Nutrient Tool.
The Solvita® Soil Test is a technology and method that is easy to perform which accurately measures soil CO2 respiration. There are two differing applications of the test, one for soil labs and one for field investigations:
CO2-BURST:STANDARD LAB PROTOCOL
Dried, weighed samples of soil are moistened with a specific amount of water, triggering a flush or “burst” of carbon dioxide. The magnitude of the burst is measured with the Solvita Digital Color Reader (DCR). The CO2-Burst is proportional to microbial biomass and directly tied to potential carbon and nitrogen mineralization.
Fresh, field-moist soil is evaluated for background or “basal” CO2-respiration by filling the test jar to volume or in the field by using a 3” cylinder inserted in the soil. The results serve to indicate general soil health and carbon dioxide emissions per surface area. It is a useful tool for evaluating effects of cover crops, different intensities of soil management, and potential carbon sequestration.
SLAN:Solvita has developed a new lab test that measures a pool of organic N present in soil that may be fairly available and relates to soil management. Evidence that these nitrogen complexes consist of amino groups is demonstrated by addition of alkali to a soil sample with resulting production of free ammonia (NH3). The new Solvita application releases this alkali-labile soil amino-N from soil by addition of NaOH and simultaneously traps it in a visual indicator gel (Solvita Ammonia-Probe®).
Solvita CO2-Burst Soil protocol: A weighed sample of dry soil is placed in a jar with added water, and the pulse of CO2 measured with Solvita probes.
SOIL HEALTH TOOL: This new protocol introduced by USDA-ARS incorporates the Solvita CO2-Burst test into a more comprehensive package that also includes nutrients extracted by a new type of “green chemistry” soil reagent. The “Soil Health Score” is separately calculated based on the Solvita result in relation to water-extractable carbon and the organic C:N ratio. Some commercial labs in the country are now offering this additional method (see SOLVITA MAP). To learn more about this application visit Woods End Laboratories.
The Basic SOLVITA® Soil Response Color System
The patented gel-technology system indicates CO2-respiration over a color range of 0 to 5 (see chart). In CO2-Burst mode this corresponds to a range of 5 to 175 ppm CO2-C. In BASAL mode it corresponds to a range of 0 – 55 ppm or 1 – 25 kg m2/year as CO2.
All Solvita kits work with a basic visual color system, as shown below. By using the Solvita Digital Color Reader (DCR) the soil test values can be more accurately and precisely determined.