November 8, 2013
In our last blog post, we mentioned that Iowa State has updated their Potassium recommendations to support field moist measurements. We are honored to have this level of support after having our lab open for just one year. Following this post, many agronomists have reached out to us to ask us if drying has an effect on K levels in other states as well. Iowa has the most calibration data for field moist tests (and the oldest, going back several decades) but the effect has certainly been observed in other states. We wanted to write a short post to describe what we know.
First, some background on why this isn’t just about Iowa
Fixed nutrients tests (like P and K) are designed to measure the nutrient level that is available to the crop throughout the year. Very little potassium is available in the solution form at any given time. As the crop takes this potassium up, more potassium becomes available from places where it is loosely bound to the soil. Laboratories use chemical extractants (like Bray, Ammonium Acetate or Mehlich 3) to measure both the amount of nutrient and the easily exchangeable component that the plant can access to get a reading that is relatively stable over time. I recently found a post on smart-fertilizer that does a good job describing this fundamental understanding of potassium in soil, which is the same all over the world.
So why is it important to measure potassium in the field moist state? Potassium is often held in the interlayers between clay minerals. These interlayer spaces expand when some certain kinds of clay minerals get dry, allowing the fixed potassium to behave more like the easily exchangeable form when exposed to a chemical extractant. Other kinds of clays to not expand at all. Thanks to the effect of glaciers many different kinds and concentrations of clays can be found in the same field. What’s more, the amount of potassium that comes out when the expanding clays dry out depends on their history. Many soils with very little plant-available potassium can release potassium while other soils that do not have clay between their inter layers can actually fix potassium when they become dry. This effect has been observed in various places throughout the world.
What we’ve seen
Solum has been working with various industry partners to understand the best ways to measure potassium for a number of years. In 2011 we conducted field trials with 15 retail partners across Iowa, Minnesota, Illinois and certain surrounding states. In 2012 and 2013 we expanded this group to work with Winfield Solutions and a larger group of universities. The image below summarizes our results. Green states are where we have seen a significant effect, in most cases over several years. Yellow states are where results are inconclusive or unknown.
Who else is working on this
Solum is not alone at look at the effect drying has on Potassium. Academic teams in South Dakota, Minnesota, Illinois and Indiana (and perhaps others) are currently conducting research and several of them have made statements about the effects. Mosaic and IPNI have participated in grant funded studies and Winfield has included field moist measurements in nation wide studies as well. At least one other commercial lab is offering the test and we hope to work with other labs soon. The Agriculture Laboratory Proficiency Program is even experimenting with a new quality control program that is based on field moist soil. We are excited about being part of this process and in being involved in a new level of collaboration between labs as we recognize soil testings central role to better fertility management in an increasingly data intensive world.