Did you see where soil potassium (K) only went down by 1 ppm after 374 mm (14.7 inches) of rain?
In that same comparison of pre- and post-rain samples, the soil calcium (Ca) went down by 26 ppm. The Mehlich 3 Ca was 666 ppm in the sample collected on 21 August 2019. Then it rained 347 mm over the next 11 days, and a soil sample collected on 1 September 2019 had Ca of 640 ppm.
Why did Ca go down with rain, but K didn’t? I reckon it’s because irrigation was supplying about 26 times more Ca than the grass was using. And all that extra Ca has to go somewhere.
If you are interested in the math, it goes like this. And it’s just a coincidence that it is 26 times more Ca in irrigation water than grass use, and 26 ppm decrease. Those 26’s aren’t connected in any way.
Irrigation water calcium
The most recent irrigation water analysis at Keya GC found 18.62 ppm (mg/L) Ca in the water. Adding 5 mm of water in a day would supply 93.1 mg/m2.
Calcium use by the grass
Clippings are collected from the greens at Keya GC after mowing, and the volume of those clippings is measured. In August, a typical daily #ClipVol is about 15 mL/m2.
I estimate that the ratio of volume to dry weight for korai clippings is 1:0.11. For every 1 mL of korai clippings, the expected dry weight is 0.11 g. That 15 mL of ClipVol weighs about 1.65 g.
Leaf nutrient analyses were conducted monthly from the 11th green at Keya GC in 2019, and the average Ca content of the clippings was 0.21%. In those 1.65 g of clippings harvested in a day, that works out to a daily Ca harvest of 3.5 mg.
26 times more Ca
With 93.1 mg of Ca added in irrigation in a day, and 3.5 mg of Ca harvested, that’s 26 times more Ca added than the grass can use.
Andrew McDaniel doesn’t bother adding Ca to these greens.
He hasn’t added any Ca for years. There’s no need to. And when the irrigation water adds 26 times more Ca than the grass uses, of course it leaches.