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Stage of Maturity and Time of Season

Grass forage declines in K content with increased plant age. Plant uptake of K is very high early in the season, but later on K uptake cannot keep up with plant dry matter accumulation and is diluted out. Potassium content of orchardgrass has exceeded 4.5% in late May in our studies. Grass harvested at flowering may have half the K concentration as grass earlier in the season. Concentration of K in grasses also tends to be significantly lower in regrowth, and also lower towards the end of the growing season. As a result, the grass forage with the highest K content is usually in the spring harvest. Although species vary in forage K concentration, cultivars within any given species are not significantly different for forage K concentration.