Agriculture Reference
In-Depth Information
Potassium
Potassium is involved in many plant processes, but extra potassium is not needed in the
soil of most home or market gardeners who are using compost and mulch. Everywhere I've
lived, I've had to worry more about getting the phosphorus up in relation to potassium, so I
haven't wanted to add too much extra potassium. It is important, though for determining
the caliber of the stalk and leaves and the size and set of the fruit, among other things.
Compost made with lots of green matter and a bit of manure generally provides plenty of
potassium.
Traditionally, we go for 2-5% potassium on a base saturation test and a 2:1 phosphate to
potash ratio on a Reams test, up to 4:1 for grasses and greens. More recently, some consult-
ants advocate the upper end of the 2-5% range in order to ensure we have more potassium
than nitrogen in a plant tissue test. Of course, most of us don't do plant tissue testing, but
just knowing that we should try to move the potassium towards 5% and not over-apply ni-
trogen is helpful. On the other hand, too much potassium compacts the soil.
Langbeinite supplies potassium and was mentioned in the magnesium section. If my soil
had a potassium deficiency, I might also use some seaweed if I could get my hands on it, as
well as granite dust and ash. Granite dust is 3-5% potassium, while wood ash can have a
potassium content as high as 10%.
