Looking Back to 2012

It is hard to predict the impact of the current dry fall on soil sample results. Only after the sampling season is over can we determine if the dry weather impacted soil test results.  What we can do is look back at previous years and learn from experience.

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. Given that the drought set in for most of the ALGL service area later in the year after crop establishment. 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 from the soil. A simple reference is that when tiles are flowing water, water is infiltrating down through the soil profile and taking soluble salts with it.  

For comparison this year is much like 2012 for many areas. During a severe drought, water pH readings may be 0.1 to 0.6 pH units lower than expected. Looking back, pH data from 2012 does not stand out in the long-term data and indicates that the drought did not significantly impact soil pH in 2012.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 produce normal yields, less potassium may have been taken up by the crop. Looking back, potassium data from 2012 is slightly below trend, it does not stand out in the long-term data and indicates that the drought did not significantly impact potassium soil test level in 2012.