What defines a healthy or unhealthy soil? If you interview five extension agents you would get ten answers. These could range from how well microbes release plant nutrients to how the soil stands up to a heavy rain. Regardless, most farmers know an unhealthy soil when they work one, no test required. However, if producers take steps to improve their land, some may want to know if they are going the right direction.
Seeing this need, companies developed soil health tests for farmers and gardeners. The most famous one is the Haney Test, but newer ones that focus on microbes are quickly arriving on the market. With this flood of new products, it is vital that a grower knows these new tests’ limitations before any shovel breaks ground.
A key reason to be cautious is expense. A soil health test can be as high as $40-80 a sample—two to five times more than a standard fertility test. This added expense can be difficult to pencil out, particularly for farmers in a tight agriculture market.
To justify their expense, some products may also give fertilizer recommendations. Currently, the University of Minnesota does not endorse use of these in the field. Any production increase from these alternative tests should pay for the application as well as the sampling. Preliminary research conducted by the University of Minnesota suggests the well-known Haney Test could lead to over application of nitrogen and potassium.
Another caveat to watch out for is soil health “scoring”. This too must be taken with a dash of salt. Laboratories tend to calculate these scores differently and do not separate them by state. Frequently, they fail to take into account sampling dates, crop, or soil texture. This could lead to a situation where a “below average” soil in Maine is an “above average” soil in Minnesota.
Additionally, soil health measurements tend to be a “snapshot” of current conditions. For example, moisture and temperature are notorious for affecting microbial or carbon tests. Sampling one field on a dry day and another after a drenching rain could cause any differences between fields to be exaggerated.
To reduce error, compare soil health measurements between fields that differ in management rather than landscape. If you are searching for a goal for your soil health values, consider sampling an uncropped area near the field you are curious about. This could include a fence row or somewhere where living roots are present year-round. Regardless of where you try these tests, sample on consistent dates and weather to minimize variability.
If you are curious about purchasing these products, I recommend discussing them with a trusted agronomist or extension educator. Soil heath tests can help fill in knowledge gaps on our land and give a rough idea regarding how well the land can function. However, the flood of information they provide needs to be sifted with care, and not used as a sole reason for a farm or garden decision.