Soil labs have traditionally been reluctant to offer soil biology tests, partly due to costly, complicated (and outdated) methods. Renewed interest in soil quality is increasingly motivating researchers and growers. “For too long, its been believed that soil biology is of academic interest only – or an exclusive domain of organic growing alone. But now, evidence for the direct link of nutrient release with humus-carbon turnover, a biological property, obviates this view. As Dr. Haney states: “why overlook free fertilizer?”
Woods End and its partner, the USDA-ARS soil lab in Temple, Texas have been running comparison of soil respiration and nitrogen mineralization using a number of traditional methods. One test called 7day N-min, has shown surprisingly good correlations to the rapid CO2-burst method that Solvita and USDA have developed (see figure). The 7-day N-min measures microbial activity and nutrient-release in an indirect, time-consuming process, and labs are hesitant to use it, or if they do, they have to charge more than farmers may be willing to pay. “Yet the information is vital to understanding how to save costly nitrogen fertilizer- without loosing any yields – plus it shows you something important about soil biological health”- Brinton of Woods End states, who invented the test in 1996, but has seen this many years go by in realizing the application.
PARTNERSHIP: The new soil Solvita CO2-burst protocol is a unique collaboration of Government and Private Lab: Woods End Laboratories and Dr. Haney’s USDA-ARS soil lab in Temple, TX, both centers that had been pursuing soil quality for 25 years. The new protocol puts the measurement of soil microbial activity into the realm of the practical and is cost-effective for commercial soil labs to perform.
WHY TEST SOIL MICROBES: The quantity of active soil microbes – fungi and bacteria- can be represented by actual living carbon associated with “respiring (live) cells producing CO2 within a soil systems” – from Dr Haney and Brinton. This living microbial consortia is associated with many positive properties such as transforming chemicals, aiding pesticide degradation, facilitating the release of nitrogen from organic matter and contributing to soil aggregation. The latter property alone may account for more than 50% of soils ability to resist erosion.
RELEASE of “FREE” NITROGEN: Measuring microbial activity is not the same as determining total organic matter (SOM) or total-C, and then estimating the potential release of nitrogen – a method which some labs have relied upon, but which can give remakably inaccurate results. 7d N-min will actually measure the nutrient release but under harsh circumstances of 40°C anaerobic incubation. Other tests the team has used are direct 28-day mineralization of nitrate and ammonium, showing similarly good correlations. Added to the roster are crop uptake studies which are showing that the amount of nitrogen present in unfertilized crops- called “controls” – closely corresponds to the amount predicted by the soil biology test. “There is a great deal of interest in showing how this biological function behaves in different growing regions” says Brinton.