Daniel Hudson, UVM Extension Agronomist
While routine soil sampling in the fall is preferable, spring soil samples can still provide practical guidance for the upcoming cropping season. As the parent material (originated from rock) and organic matter in the soil weathers and decomposes, plant-available nutrients are released. These chemical and biological processes typically result in a peak concentration of plant-available nutrients in the spring/summer. Concentrations of plant-available nutrients will vary during the year and be driven by: soil texture, crop uptake, soil temperature, soil moisture, precipitation/leaching, soil pH, biological activity, compaction, soil organic matter, crop history, manure history, and other management factors.
Soil sampling at the end of the growing season is preferable, but spring sampling can still be helpful
Long-term, it better to collect your soil samples in the fall after corn harvest or after your last cut of perennial forages, but prior to manure application. This should give you the best view of your baseline level of plant-available nutrients and help you understand the ideal approach to soil fertility management on each field next spring, or each spring until your next soil test is due.
It is similar to assessing your firewood inventory after you stoke your wood stove for the last time in the spring. You may have a bunch of wood left, it could be mostly gone, or you may have run out in March. That information is obviously useful for making plans.
The difference is that your plant-available nutrients in the soil are generally lowest at the end of the cropping season, and thus the recommendation to test at that time. If a particular nutrient was critically low after harvest last September, it will probably be critically low at certain points in the coming growing season unless improvements are made to the nutrient management process.
If you don’t have current soil samples for your fields, DO take samples this spring, but plan to move toward establishing a late-season soil testing program in the near future.