I look forward to some photos from Doug Soldat. For the past three years, he's had some fascinating photos to share of snow mold on creeping bentgrass. And each year, there was more snow mold where potassium fertilizer was applied, and less snow mold where potassium wasn't applied.
Spring of 2014
In the spring of 2014, there was more snow mold where K was applied.
Snow mold post was pretty popular today, so here's a combined pic. Numbers are lbs K2O/M/yr. pic.twitter.com/rTVG0jOrzd— Doug Soldat (@djsoldat) April 2, 2014
Spring of 2015
Last year, there was also more snow mold where K was applied.
Pink snow mold on 'A4' bent sand green in WI. No K for 4 yrs on right, 0.2 lbs K/1000 every 2 wks for 4 yrs on left. pic.twitter.com/VSMlhcUmnv— Doug Soldat (@djsoldat) March 21, 2015
Spring of 2016
This year, it happened again. There was more snow mold where K was applied.
No K on left, 0.1 lbs/1000 every other week on right. pic.twitter.com/9LoYCWcuHS— Doug Soldat (@djsoldat) March 23, 2016
Doug will be talking about K in a TurfNet webinar in April: Is Your Potassium Program Hurting or Helping Your Turf?
On those creeping bentgrass plots in Wisconsin, adding K increases snow mold. No K had less snow mold.
At Rutgers, annual bluegrass plots deficient in K have had more anthracnose in summer and more winter injury. Eliminating the deficiency reduced those problems.
Then there is the MLSN guideline for K of 37 ppm. I recommend keeping the soil K above 37 ppm (Mehlich 3 extractant).
And there are hundreds of other studies about K. Some show a benefit from adding K, and some don't. I haven't read all of them, but I have read a lot of them. This sounds like it could be pretty complicated.
Actually, I don't think it is. Here's what seems to be the case, for both warm-season and cool-season grasses:
Ensuring the grass is supplied with all the K it can use will provide all the benefits associated with K. Adding more than that usually has no effect, other than wasting time and money, but sometimes has a negative effect.
As a turfgrass manager, all one has to do is ensure the grass is supplied with all the K it can use. This can be accomplished in 2 ways. One is by keeping the soil K above the MLSN guideline. A second is by applying N:K in a 2:1 ratio for cool-season grasses, a 1:1 ratio for seashore paspalum, and a 3:2 ratio for other warm-season grasses. I wrote about that in the final chapter of A Short Grammar of Greenkeeping and in The (New) Fundamentals of Turfgrass Nutrition.
Note that I do not recommend tissue testing for K (or any other element).
If you want to read more about K specifically, and about how the benefits of K come from correcting a deficiency, I recommend: