Each crop year has unique weather. Some areas of the northern Great Plains have experienced drier than normal moisture conditions and warmer than normal temperature conditions.
In some of these areas, ample soil moisture conditions early in the growing season resulted in excellent early crop growth, but ran short because of the lower than normal growing season precipitation. Crops ripened earlier and yielded less than expected.
Lower yields due to dry conditions usually means there is a higher than normal carryover of nitrate nitrogen (NO3-N) in the soil.
Read Also
VIDEO: Green Lightning and Nytro Ag win sustainability innovation award
Nytro Ag Corp and Green Lightning recieved an innovation award at Ag in Motion 2025 for the Green Lightning Nitrogen Machine, which converts atmospheric nitrogen into a plant-usable form.
For farmers fortunate enough to live in an area where growing season moisture has been adequate and not excessive, the excellent crops will have removed most of the NO3-N in the soil and soil test nitrogen levels will be less than normal for the area.
Either way, if the warm weather has encouraged the crops to mature faster, an early harvest opens up the possibility to take soil samples sooner in the fall, according to Tom Jensen, the northern great plains director for the International Plant Nutrition Institute in Saskatoon.
Fall soil sampling on fields in the northern Great Plains is generally delayed until early October, but there are advantages in beginning soil sampling soon after crops are harvested:
- There is more time to take soil samples to allow informed decisions for overall fertilizer recommendations, especially if fall nitrogen applications are considered. Fall applications are usually cheaper than spring applications.
- Poor weather later in the fall may interfere with taking soil samples, especially if winter comes early.
- Sampling right after harvest can be completed before use of residual soil nitrogen by volunteer crop growth. Much of the nitrogen used by volunteer growth in the fall is leached out of the frozen and dead volunteer crop residues and becomes available to next year’s crop.
The only disadvantage of early fall soil sampling is in a year when ample early fall precipitation is followed by warmer than normal conditions well into the fall.
This type of condition can allow extra mineralization of nitrogen from soil organic matter.
This extra soil mineral nitrogen will not be present when the soil was sampled earlier, but will be available to next year’s crop. If such a fall season happens, it may be beneficial to take additional soil samples from selected fields early the following spring to determine the extent of fall nitrogen mineralization. It is often not more than 15 to 20 pounds of extra nitrogen per acre.
Research has shown little if any need to delay soil sampling on perennial pasture and hay fields. Perennial forage stands tend to use residual NO3-N effectively and little is left over.
The exception may be recently seeded stands where the root systems of the forages may not be extensive enough to use the nitrogen present.
