A well-structure soil (top) absorbs water well without a loss of air-pores, and generates a huge CO2-pulse. An unstructured soil (bottom) will over-saturate and inhibit the natural microbial response from an infusion of water into dry soil.

Soil health testing needs its own set of calibrations and guidelines in order to have its potential fully realized. This has come into focus recently with studies on how soils behave biologically. Normally, when a soil dries out, a sudden addition of rain or irrigation water produces a well-known effect – the “CO2-Burst” – a surge of respiration by microbes springing into action. This has been linked to release of nutrients – and to a rapid boost in plant growth. Since the phenomenon was first reported in the 1950’s scientists have put forward various explanations such as “lysis” – a feast on dead microbes, to enzymes that accumulate in dry soils. Regardless, the Solvita test simulates this phenomenon by adding a charge of water to dry soil and it captures the resulting pulse of CO2 over 24 hours (the effect may last up to three days). This burst reveals soils “biological potential” which Brinton says is analogous to “coiled spring” opening up suddenly,- a gift of nature and fine-tuned to growing plants when water arrives.

Yet, an increasing number of Solvita tests are revealing the opposite effect. “We’re seeing moistened soils go into a biological slump, instead of the burst” says Will Brinton, Solvita developer who has recently connected the trait with structurally impaired and damaged soils.  This means that the test may be revealing something related to “infiltration” – the positive property of well-aggregated soils absorbing and retaining moisture after heavy rainfall without a negative effect. The opposite of this, in poor soils is a biologically suppressed response, since the soil structure cannot support the air it requires when water arrives.

Brinton calls the phenomenon “water stress respiration”.  One northwest farmer on pivot irrigation may have corroborated the CO2 slump Brinton observed in the lab by pointing out that his soils go into a “performance slump” after heavy irrigation – suggesting that his soils are biologically sensitive to high amounts of water.

Meanwhile the Solvita team is working to make sure that lab handling methods such as drying and grinding don’t also trigger the effect. Over-pulverizing soil makes it susceptible to water saturation which adversely affects the biology.  “In the end a lot of this has to be a conversation between the lab and the farmer, helping build region-specific interpretations for these new observations. If the labs are causing it, then we need to see what in the soil is responsible.” A research report on the soil wetting issue is available under the publications tab.