Are the nutrients on my soil test truly available?

By Adam Cook, director of agronomy, Top Soil crop & soil health center

Nutritious feed from your crops starts with your soil. We all see the exchangeable pool of nutrients on our soil report, but how do we know what is truly available today or what may become available?

First off, we can measure the plant-available pool of soil nutrients with a Haney extract. The Haney extract is designed to mimic the exudates of plant roots rather than use the common harsh acid soil test extractants.

Farms may often have tremendous levels of phosphorus and potassium on our standard soil test, but the yield doesn’t correlate. The Haney tests on that same field may show plant-available nutrients as low or medium. One focus should be on potential tie-ups such as high magnesium inhibiting potassium availability, or high pH and very high calcium levels tying up phosphorus.

In addition to nutrient levels, the Haney soil health test also focuses heavily on soluble carbon, known as water-extractable organic carbon (WEOC). When we compare WEOC to our soil’s cation exchange capacity (CEC), we can begin to gauge how good our soil is at cycling nutrients on its own and what will likely be released during the growing season. Dividing soil into mineralization zones based on waterflow and accumulation, topography and soil texture often reveals that the rates of mineralization and the plant-available nutrients will vary significantly across the field.

A second focus is looking at the balance of micronutrients and macronutrients. Is there enough zinc and copper to support the phosphorus? Was enough sulfur provided to allow the plant to uptake all the nitrogen and potassium that was applied?

While manure is nature’s best source of fertilizer, it often doesn’t have the ideal nutrient balance needed for the perfect plant or it can’t overcome natural soil imbalances. This is why we test our rations and supplement the nutrients that may be short. Homegrown feed in different regions of the United States is often lacking in different nutrients, which can be tied back to the soil and the characteristics of the parent material. Animal nutrition and soil nutrition should never be one-size-fits-all in every geography. Advanced testing gives us better data to make better decisions.