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Seed Production of Kentucky Bluegrass Associated With Age of Stand¹

Perennial cool-season grasses generally show a characteristic decline in seed yield associated with age of stand. This study was designed to document the effect of age of stand on seed yield and associated plant growth characteristics. Clones of ‘PNW 602’ Kentucky bluegrass (Poa pratensis L.) were planted in spacings of 30, 60, and 90 cm each year for 5 successive years to produce 5 chronological-age crops which could be harvested in the same growing season.

There was no significant difference in the five-crop average seed yields for the three plant spacings. The highest seed yields (over 500 kg/ha) were secured in the first and second crops for plants spaced at 30 and 60 cm and in the fourth crop (467 kg/ha) for plants spaced at 90 cm. The fifth-crop seed yields were 49, 37, and 62% of the production of the high-yielding crops for the 30, 60, and 90-cm spacings, respectively. These data contained no evidence that plant spacing would affect the decline in Kentucky bluegrass seed production associated with increased age of stand.

The decline in seed yield of Kentucky bluegrass as the plants aged was associated with declines in forage yield, plant height, number of panicles, root and rhizome production, and etiolated regrowth. Seed weight/panicle showed a tendency to decline with age of stand but had a strong negative association with panicle numbers.

The data indicate that good quality seed can be produced from older Kentucky bluegrass stands. Seed weight did not show a decrease associated with age of stand but tended to have a negative association with seed yield. Germination of seed tended to decrease with age of stand with significant reduction in the fifth crop of the 30 and 60-cm spacings.

Key Words: Forage yield • Plant height • Panicles/m² • Seed weight/panicle • Weight 100 seeds • Germination • Root and rhizome weights • Etiolated regrowth

² Research agronomist, ARS-USDA; and professor of agronomy, Washington State Univ., Pullman, WA 99163.

Received for publication May 10, 1975.

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