The Haney soil health test, named for U.S. Department of Agriculture scientist Rick Haney, includes more than a dozen different soil-test values. Those include standard macro- and micro-nutrients for plant consumption, but what’s different about the Haney test is that it also estimates nutrients for microbial consumption, focusing on how much carbon and nitrogen is in the soil.
Those are sub-pools of the total soil organic matter, like soil respiration, water-extractable carbon and water-extractable nitrogen. Those pools are correlated with total soil organic matter, so if there is a greater percentage of organic matter there should be greater microbially available organic matter.
The Haney test is intended to select robust soil biological activity even if the overall percent organic matter isn’t great. But it’s an open question of what “enough” biological activity is, so interpreting tests like the Haney can be difficult.
The soil food web starts with plants, which fix carbon dioxide from the atmosphere into organic carbon compounds. Microbes and grazers, like earthworms, eat that organic carbon and respire carbon dioxide themselves. Other larger organisms act as predators.
Consider some points when looking at Haney results or when conducting a Haney test.
- Soil biology doesn’t stop. The Haney measures microbially available pools of carbon and nitrogen as well as microbial respiration potential in a lab incubation. Those are just snapshots of organic matter pools and fluxes. Those pools are constantly being replenished by plant root exudates and dead microbial cells. It’s liable to change rapidly. So look for trends, not absolute values.
- Respiration doesn’t differentiate between food source and microbial capacity. Both are good things, but a high soil respiration value could be due to lots of simple carbon sources for microbes or a large microbial population. Values will tend to be greater in higher organic matter soils and after fertilizer application stimulates microbial activity.
- Haney fertilizer recommendations have not been tested and calibrated for a particular state. Thousands of research plots have gone into University of Minnesota recommendations for fertilizer applications. There are only perhaps a few dozen test plots examining Haney fertilizer recommendations, and none are in Minnesota. Plus Haney tests don’t capture the total soil nutrient pool because they only sample the top six inches.
- Don’t bank on the nitrogen release value. That is based on an “average” four times per season when sufficient rainfall will release nitrogen. As everyone who has farmed through the past couple of years knows, the average season is probably not relevant to many seasons.
- Changes in soil biological tests can take a long time. Despite many claims of rapid organic matter increases, tests don’t always reflect management changes. Pay attention to plant health, water infiltration, and soil structure and retention. If there’s improvements in those functions, don’t worry too much about the tests. If curious about soil biology, sample every few years at the same time, under the same conditions and look for trends, not absolute values. Compare to a nearby undisturbed area for the best benchmark of a soil’s potential.