Dave Franzen
Extansion Soil Scientsit
NDSU – Fargo
701-231-8884
It 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:
- 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.
- 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.
- Regrowth of volunteer grain will not hide available nitrogen. Early sampling will show the nitrate that will be available for
next years crop.
- Sampling right after harvest guarantees that fields will get tested and not missed due to weather problems that could happen
later in the fall.
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