Impacts of the Dry 2024 Fall

During the dry soil sampling in the fall of 2024 there were quite a few questions about how the drought conditions in much of the ALGL trad area were impacting soil test data. At the time it was very hard to predict the impact on soil sample results. The resulting 2024 data has a much clearer picture. While the data presented in this article is for the entire ALGL trade area, like in 2012, the entire ALGL trade area was impacted by drought in 2024.

During extended periods of dry weather / drought, soil pH is impacted by an increase in soluble salts in the soil solution that haven’t leached downward through the soil profile during a prolonged severe drought. The soluble salts do not actually change the pH, rather it interacts with the soil pH probes there at the lab leading to the lower reading of 0.1 to 0.6. Given that the drought set in for most of the ALGL service area later in the year after crop establishment the impact should have been reduced. In our cropping systems the main salt inputs are fertilizers and manures. The salt from application in the fall of 2023 should have leached out of the sampling zone over the winter. While spring rain was not heavy in most areas, there was enough to leach most of the soluble salts resulting from spring 2024 applications below the sampling depth. A simple reference is that when tiles are flowing water, water is infiltrating down through the soil profile and taking soluble salts with it.  

Looking at the soil pH data for 2024, the soil pH on average was not notably different than past years.

When soils remain extremely dry for extended periods of time, the space between the layers of shrink-swell clays, those that form large crack in dry conditions, gets smaller. This traps potassium between the clays layers that prevents the inner clay layer potassium from replenishing the available potassium in the soil solution as it is diminished through crop uptake. This can show up as a reduction in the soil test level. Also, potassium is easily leached from crop tissue following harvest. With little rainfall, this potassium reserve could remain in/on the crop tissue. One caveat of this, though, is with inadequate moisture to support optimum plant growth, less potassium may have been taken up by the crop. Looking to the 2024 potassium data, it resulted in above average soil test results and comparable to 2023. While isolated regions/area may have been impacted more, on average the dry soil conditions do not appear to have had a significant impact on soil test K results.

What is interesting about the 2024 potassium data is that there appears to be an upward trend in soil test potassium developing. Over the past 5 years the soil test K levels have increased on average with a corresponding decrease in the percentage of low testing soils. While it is still too early to make that statement with this data set, the trend may be developing.