Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 1997
Publication Date: N/A
Interpretive Summary: Although Thurber needlegrass provides valuable forage on many Pacific Northwest rangelands, there is no information available on how grazing affects subsequent forage production and forage quality. Typically, if grasses are ungrazed during the growing season their nutritional quality becomes so low in late-summer that cattle can not even maintain their weight. Thurber needlegrass was clipped at different times during the growing season to see how much regrowth it could produce and to determine the nutritive value of regrowth late in the summer. In a dry year less total forage was produced if needlegrass was clipped during the growing season. In a wetter year more total forage may be produced if plants are grazed either mid-way or late in the growing season. In either wet or dry years the forage quality of the regrowth was high enough in late-summer, after the plants had stopped growing, that cattle should be able to gain weight or at least maintain themselves by returing to a previously grazed needlegrass pasture. If a pasture is grazed twice in one year, it should be allowed to complete its growth cycle before it is grazed the following year. This study showed that grazing can be used to condition forage for late-season use. Both livestock and wildlife should be able to produce acceptable gains for a longer period of time in pastures that support regrowth, and producers can save their more expensive harvested forages for latter use or market the excesses that are not needed.
Technical Abstract: Thurber needlegrass provides valuable forage on northwest rangelands, but little is known of its qualitative and quantitative responses to defoliation. Cohorts of Thurber needlegrass were seasonally clipped to a 2.5-cm stubble to describe initial growth rates, determine effects on subsequent regrowth production, relate regrowth potential to soil moisture, and determine the nutritive value of initial growth and regrowth for cattle. Although rainfall for the 1985-86 treatment years was, respectively, 77 and 111% of the long term mean (25.2 cm) initial growth rates were similar between years. Seasonal regrowth yield varied between years, and was well correlated (r2=0.76 to 0.80 P<0.05) with soil moisture content. Among 7 clipping dates (24 April-17 July) only the first 5 yielded regrowth in 1985, and all produced regrowth in 1986. In both years total herbage production was most affected (47- 63% decline) by clipping during the early-boot stage of growth. In 1985 when conditions were drier, any defoliation before mid-June reduced total herbage yield. Crude protein of needlegrass herbage was high (19-22%) when growth began in April but declined to marginal levels for cattle (6.7-7.7%) by mid-July. Regrowth harvested on 31 July ranged from 7 to 9% CP for the earliest (24 April) treatments and as high as 17% for the latest (17 July). If planning 2-crop grazing regimes for Thurber needlegrass one should base scheduling on plant phenology, soil moisture, and historic use rather than specific calendar dates. Needlegrass pastures exposed to a 2-crop harvest should be deferred for at least one growing season or longer if conditions are droughty or grazing occurs in the early-boot stage.