What’s in Your Soil?

Knowing what’s in your soil helps you……..

• Save money.
• Protect water quality.
• Grow better crops.

You need nitrogen to turn those Average Joe crops into top-notch superstars that return high yields.  Now, If it was only as simple as applying any ol’ amount of nitrogen fertilizer to your crops, you’d be hitting homeruns over the fence for every harvest. However, nitrogen sometimes plays in a different game, ignoring play calls and throwing curve balls at your growing season.

N makes up a very active member of your team.  Nitrogen is a tricky nutrient for growers to manage because it’s always changing.  Sometimes it’s in the proteins of organic matter.  And sometimes it’s broken down into simpler ‘available’ forms, like ammonium and nitrate.  From there, it may leach out of soils or be taken up by plants or microbes, where it becomes part of organic matter again.

To complicate things further, the total amount of nitrogen in the soil continuously changes.  In addition to leaching loss, nitrogen can also evaporate, or volatilize, when soils are wet.  Or, in some cases, you may end up with more nitrogen in the soil. Soybean (legume) roots add it to the soil by fixing it from the air. Compost, manure, or fertilizer also increase nitrogen levels in the soil. And even nature plays a role in increased amounts of nitrogen if organic residues build up over time, increasing the levels of organic matter in the soil.

Mineralization Matters

The release of available nitrogen from decaying plants, compost, manure, or soil organic matter is called mineralization. Think of this process as lunch for soil microbes with poor manners. The microbes gobble up those materials then spit out any extra nitrogen they don’t need to build their bodies.

One of the largest impacts on the rate of mineralization is environmental conditions. Microbes tend to be especially active and eat more when the soil is warm and moist and sleepy if it’s cold and dry. Kind of like a bear in hibernation.

How Does SoilSens Fit In?

SoilSens is like the coach on your team. It measures the amount of nitrate nitrogen that is available in the soil, providing information so you can help your crops perform at their best.  It calls in the help of one of the team’s most important players—water.  Obviously, crops need water, regardless of how fertile the soil is, or they’ll die from starvation. Water serves as the transfer mechanism—the super highway that carries the nitrate ions to the plant—for the fuel source.  As they’re carried along this super highway, nitrate ions are absorbed into the plant’s roots.

SoilSens utilizes this natural process, mixing soil samples with deionized water, to measure the nitrate ions transferred from your soil into the soil slurry mixture.

The significance of knowing the amount of nitrate nitrogen currently available allows you to fine-tune your nitrogen fertilizer applications, making sure the crop has what it needs without wasting money over-applying fertilizer or potentially threatening the water quality.

Measuring Nitrate Ion Levels

While measuring soil nitrate ion levels is a time-tested way of measuring soil quality, it has not been traditionally used by soil laboratories.  Soil laboratories normally use a method called KCI Extraction/Cd-Reduction.  Essentially they extract the nitrate from the soil, mix it with a chemical that changes color in relation to how much nitrate is present, and then measure the color change.  The method has the advantage that it is easy to automate in a lab environment.  It has the downside of using Cadmium, which is a hazardous material.  It also requires the soil to be dried, which can cause significant changes in the soil nitrate contents.

While SoilSens has the advantage of using field fresh soil and being portable, it does not have the same established history as the lab tests.  Therefore, interpreting SoilSens results will differ from traditional lab results.  Below is a guide that shows how to interpret SoilSens results:

SoilSens Test Results                      Interpretation

Less than 3 ppm                              Very likely N deficient, side dress N is recommended.

4-10 ppm                                         Low, but may be sufficient for a medium-yielding corn crop.
10-20 ppm                                       Sufficient N is available for most crops. For highest yields,
                                                      some N should be added.

20-30 ppm                                       Side dress N is not recommended.

Greater than 30 ppm                         Excessive N already present.

Note that in years with unusually dry spring weather, soil nitrate concentrations typically will be higher than normal; in years with unusually wet spring weather, soil nitrate concentrations typically will be much lower than normal.  The only way to know what constitutes the normal range of soil nitrate concentrations for your soils and N management is to test your fields for a few years in a row and maintain records of the results. With patience, follow-up, and steady analysis, you can form a winning team and hit yields out of the ball park!