K is for Complication

K is for Complicated from Central Valley Ag on Vimeo.

by Mike Zwingman

by Mike Zwingman

This will come as no surprise to all the regular followers out there; I have a fascination with Nitrogen. The journey with Nitrogen has lead me to curiosity with Potassium due to the relationship and interaction between these two nutrients. What I learned is, available plant Potassium in the soil is more complex than Nitrogen. Every year we get asked the same question, “How is it that I have plenty of Potassium in the soil yet am deficient in the plant?” In today’s article, I plan on shedding some light on that very question.

The interesting thing about the Plant Potassium and Soil Potassium relationship is it is like a lot of relationships that we encounter as humans every day. The fact it is all about chemistry and timing. The Chemistry is that the Potassium must be present in the soil. Here is where the first misconception comes into play. When we normally talk about soil Potassium, we talk about exchangeable Nitrogen and the Cation Exchange Capacity (CEC) of the soil and Exchange Sites; then we go on describing the CEC and exchange sites by drawing something that looks like Figure 1. Then we go on describing the soil particle as something that is round and can attach cations anywhere along the outside.

The reality is our CEC is driven by the clay content and base formation of that clay. Those clay particles that are in our soil are more laminar-like plywood or more accurately a good biscuit. See Figure 2. Here is where timing comes in, because much like a good biscuit, when it is at just the right temperature and moist enough, the layers separate and all the goodness is released.

Soil temperature has to be in the low to mid 70’s and the moisture needs to be just above field capacity. Now think about the frequency of those two things happening independently, then think about them happening at the same time. Couple all of that with the timeframe and rate of demand in corn, which during grand growth is about 13lbs/A per day. Now you see why this is complicated? If we don’t get those laminar layers to expand and separate any exchangeable Potassium will not get released, and because of the mode of uptake for a plant to access Potassium, it can’t be held tightly by the soil. There is Potassium in the soil solution, but that is a nominal amount in comparison to the Exchangeable Potassium in the soil.

Fifteen years ago, when corn yields were lower, and our management was different, the soil could keep up with grand growth. Things like improved genetics, less tillage, narrower rows, higher plant populations, and improved irrigation practices have changed the dynamics between soil Potassium and plant Potassium, but so has our understanding. To continue to push the yield envelope and improve nitrogen efficiency we are going to have to master the Potassium cycle. That may mean changing how and when we apply Potassium much like we do Nitrogen. Complex systems are where we have the greatest opportunities, but they take work and trial and error. These are things we look to keep improving on with you, our partner owners, to improve the profitability and sustainability of your operations for years to come.