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Individual study: Cumulative effects of spring or early summer mowing and height of cut on yield of bluebunch wheatgrass Agropyron spicatum in native A.spicatum-Poa secunda grassland near Lacrosse, Washington, USA

Published source details

Wilson A.M., Harris G.A. & Gates D.H. (1966) Cumulative effects of clipping on yield of bluebunch wheatgrass. Journal of Range Management, 19, 90-91


Bluebunch wheatgrass Agropyron spicatum is an important perennial forage grass for wildlife and livestock in western North America. In this study, the effects of spring or early summer mowing (simulating grazing) and height of cut on bluebunch wheatgrass yieldin native A.spicatum- Sandberg bluegrass Poa secunda grassland near the town of Lacrosse, Washington, (northwest USA) was investigated.

The experiment was a randomized complete block design with 10 replications of nine clipping treatments:

1) clipped 3 April when 2.5-5 cm of spring growth (cut at 0 cm);
2-3) clipped 24 April when 12-18 cm of spring growth (at 0 and 10 cm);
4-6) clipped 11 May during ‘boot stage’ i.e. seed head development (at 0, 10 and 20 cm);
7-9) clipped 27 June when seed heads yellowing (at 0, 10 and 20 cm).
Plots (3 x 15 m) were cut once each year (1961-1963) with a sickle bar mower on a garden tractor. Samples were dried and weighed in 1961 to determine available forage at the selected growth stages. In June 1964 when wheatgrass seed heads were yellowing, plants in five 0.5 x 2 m quadrats in each plot were hand-clipped at ground level, dried and weighed.

Bluebunch wheatgrass was particularly susceptible to damage when mown during the boot stage; when clipped at ground-level for three consecutive years, yield decreased by 70% (0 cm -110, 10 cm -160; 20 cm - 250 lb/acre). Clipping at ground-level on 24 April also resulted in significantly reduced yields (180 lb/acre) than the other clipping treatments (between 210-380 lb/acre), with maximum yield (380 lb/acre) achieved under the 27 June 20 cm cut height treatment.

The authors suggest that inappropriate grazing over three or more years at the boot stage may therefore result in almost complete disappearance of bluebunch wheatgrass from the sward.
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