Soil samples provide landowners a gauge or a trend of the potential nutrient availability for the coming crop. Typically, this information signals areas of a field that exceed or fall short of the field’s current average fertility programs. High zones of fertility could suggest that a crop is not removing what it was given. Likewise, a zone of low fertility could suggest that a crop is removing 100% or more of the nutrients it was given. This is where a good grid soil test map acts as an inverse yield map over time.
You may be wondering, though, how accurate is a soil test? This is an ongoing debate, but like anything else, a soil sample report is only as good as the information that was used in its creation .
For years, the industry has waited until a crop was harvested, waited for lab results, waited for a recommendation and then waited some more before any fall application activity could take place. In modern agriculture production, this system is very inefficient for two reasons:
1. There is no time to wait with short application windows in the fall.
2. In the fall, the soils are typically dry and many nutrients could be held tightly in between clay particles. This can lead to an inaccurate determination of the trend of the field and unnecessary investment.
Thus, a more modern approach may work:
1. Test fields in the spring—either pre-plant or post-emerged—using a GPS grid. Soil should be at a more realistic moisture concentration in the spring than late fall and can provide greater insight.
- If a grower knows all summer what their fall or coming spring fertility needs are, they can negotiate price and procure their supply during the summer instead of waiting and being vulnerable to in-season supply issues and in-season price volatility.
- This system is very effective for lime application. Product can be hauled in all summer, with the applicator knowing the fields and rates. All they are waiting for is the word go, once harvest is complete.
2. Spring soil testing allows more time for lab work and reviewing results, which can improve accuracy of recommendations.
3. Variable rate recommendations can be pre-built for the desired fields during the summer and once harvest is complete, the recommendation can be compared to the maintenance removal from the yield monitor data. With current data streaming technologies, this system no longer has the logistical restriction it once did.
There are many variables that we can’t control, which is why we must manage what we can control. Spring soil testing is one thing we can do so we aren’t controlled by other factors in the fall.