Alfalfa and Potassium

Everyone that grows forages knows of the importance of potassium for top alfalfa production. Next to nitrogen, it is the next most highly required element by the growing plant. For every 1 ton of dry matter production, alfalfa contains 55-70 lbs of K2O. This means that at 6 ton/acre the crop is removing 330-420 lbs K2O/acre (or 600-700 lbs of 0-0-60). If sufficient amounts of fertilizer are not applied, the crop will absorb these nutrients from the soil and lower the potassium level in the soil.

Potassium is:

There are three forms of K in the soil:

Sometimes, when soil potassium levels are high, plants may take up more potassium than is needed for maximum yield. This "luxury consumption" (see figure) by alfalfa and forage grasses can lead to high levels of potassium in the forage part of the ration. It is important to remember that this luxury consumption is not only influenced by soil potassium levels but also the soil test level of the other cation elements as well as soil moisture and growing conditions.

In the March, 2003 issue of Hay and Forage (simply click on the link, go to the back issues in the upper left corner and bring up March 1, 2003 issue, when you get to this issue scroll down to Check Your Hay for K) there is an article that addressed some ways to lower potassium levels in forages:

These are a few suggestions that can help to manage potassium levels in alfalfa. The easiest way to lower potassium in dairy diets might be to adjust the feed ration, in this way the grower can still achieve maximum yield as well as quality of the forages.