Soil Testing (Behind the Combine?)

Dave FranzenIt is more the rule than the exception that soil sampling begins in mid-September instead of immediately following small grain harvest.  However, many growers miss an excellent window for soil testing by waiting too long.  The reason for waiting is the fear that additional nitrogen will be made available through mineralization (decomposition of crop residue and organic matter).  A review of research has shown that following small grain harvest, soil nitrate level changes very little and no sampling date adjustment should be made.  Soil sampling right after small grain harvest is recommended and has numerous advantages:

  1. Growers are more likely to actually use the test results to direct fall N application if the soil test results are in their hands soon enough to consider before fall fieldwork begins.
  2. Soil testing prior to fall tillage will result in a more consistent 0-6” sample core, which provides the best sample for testing phosphorus, potassium, %OM, zinc and other nutrient tested on the topsoil.
  3. Regrowth of volunteer grain will not hide available nitrogen.  Early sampling will show the nitrate that will be available for next years crop.
  4. Sampling right after harvest guarantees that fields will get tested and not missed due to weather problems that could happen later in the fall.