Rit Búvísindadeildar - 20.11.1995, Page 43

A note
on the diurnal variation in chemical composition
and DMD of three grasses
Bjarni Guðmundsson
SUMMARY
Diumal variation in the chemical composition and DMD of three grasses, Poa
pratensis (Fylking), Phleum pratense (Korpa) and Deschampsia beringensis
(Northcoast), were studied for three days (12-14th) in July 1993. Weather
conditions varied, from overcast with light showers to dry, warm and sunny
weather. Phl. pratense was at shooting (ll-12th ofJuly) while the other grasses
were still at a vegetative stage. The main conclusions were asfollows:
• On average, the DMD ofthe grasses was 2% lower in the moming (at 8 AM) than
in the evening (at 8 PM). The increase was most pronounced in Phl. pratense.
• In all the grasses, the crude protein content (% DM) was found to be quite stable
and not subject to diumal variations.
• The sugar content (% DM) was only found to follow a diurnal trend in Phl.
pratense, with a linear increase during the day, partty in relation to air-temperature.
• Both glucose and fructose contents were quite stable, while the sucrose content
varied substantially. A significant correlation was found between the sucrose
content and the air temperature for P. pratensis and Phl. pratense (r= 0.75 and r =
0.66 respectively). The ratio between glucose and crude protein content, which can
be used as a measure of ensilability of grasses, was highest in Phl. pratense and
lowest in P. pratensis.
• In respect to silage making, it was estimated that by cutting in the late aftemoon, 2-
3% higher DMD-yield could be expected, compared with cutting early in the day -
provided that favourable weather conditions for field drying are in sight.
Translated by Anna Guðrún Þórhallsdóttir PhD
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