In Part 1, I explained that adding potassium (K) after every precipitation event of 25 mm (1 inch) or more at Minneapolis or Fukuoka would supply from 2 to 13 times more K than the grass could use. Since there is no benefit to adding more K than the grass can use, it doesn't seem that such post-precipitation applications are necessary.
How can one determine how much K the grass will use? This calculator does, predicting how much K is required as fertilizer, all while making sure plenty of K remains in the soil as a buffer even beyond the K that is used by the grass.
And now, this calculator is available in a Japanese version too.