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Species/Cultivar Selection for Low Potassium

For New York State, our on-line program is available to provide site-specific forage species recommendations based on soil type, specifically dealing with forage for dry dairy cows (http://www.forages.org). The two primary factors to consider when selecting perennial forages species and cultivars for dry cow forage are 1) persistence and 2) K content.

Potassium content of perennial grasses has been reported from as low as 0.1% K up to as high as 7.0% K. Warm season grasses tend to be lower in K content than cool season grasses. Although species rankings are not completely consistent, orchardgrass tends to be significantly higher in K content at a given maturity stage than other grass species. Both orchardgrass and perennial ryegrass tend to be mineral accumulators, with high levels of K and other minerals, if there is an adequate soil supply of these minerals. Timothy on the other hand, tends to have less luxury consumption of minerals, when surplus minerals are available in the soil. Therefore, with moderate to high available soil K, orchardgrass may accumulate up to 1 percentage unit or more K than timothy. Under conditions of stress (e.g. drought) or low available soil K, the difference in K content of forage across species will be minimized.

There may be some differences in K content among cultivars within a grass species, but significant differences among cultivars have yet to be characterized. Breeding for low K content has rarely been attempted in grasses. Selection may be very difficult, because there is a significant effect of environment on K uptake in grasses, compared to uptake of other minerals, such as magnesium (Mg) and calcium (Ca). Breeding for high magnesium in tall fescue, however, has been attempted. High Mg may alleviate some of the problems caused by high forage K.