Íslenskar landbúnaðarrannsóknir - 01.09.1982, Síða 55

BEITARÁLAG METIÐ MEÐ MÆLINGUM Á GRÓÐRI 53
SUMMARY
Estimation of grazing pressure by use of dry
matteryield and crude protein content ofherbage.
Friðrik Pálmason
Agr. Res. Institute Keldnaholti, Reykjavík
Regession equations were calculated for
crude protein content (X) and dry matter
yield (Y) of standing herbage in grazing
experiments with sheep at 5 sites in Iceland
during the years 1975—1979. The crude
protein content is in this case considered as
a variate, depending mainly on the
developmental stage of plants, where site
conditions and fertilizer levels ars similar.
The relations between crude protein and
dry matter yield of herbage may serve to
estimate the grazing pressure on unfertil-
ized, drained peat soils in the lowland and
on fertilized soils in general, as far as can be
judged by the experimental results. The
regression equations and a short descrip-
tion of the sites, are listed in an apppendix
at the end of this summary.
At moderate and light grazing the
measured yield of dry matter, grazed
HEIMILDIR—REFERENCES
1. Áfangaskjrslur landnýtingartilrauna.
(a) 1975 Fjölrit Rala nr. 2.
(b) 1976 Fjölrit Rala nr. 29.
(c) 1977 Fjölrit Rala nr. 38.
(d) 1978 Fjölrit Rala nr. 50.
(e) 1979 Fjölrit Rala nr. 63.
2. Andrés Arnalds (1980): Mixed grazing on lowland
bogs in Iceland: Pasture efFects - Proceedings
Workshop on mixed grazing. - Galway 1980.
Agricultural Inst. Ireland, Rannsóknastofnun.
landbún. íslandi.
3. Ólafur R. Dýrmundsson og Jón Viðar Jónmundsson
(1980): Performance of sheep and cattle on a
cultivated bog pasture at Hvanneyri, Iceland. —
Proceedings. Workshop of mixed grazing. —
herbage not included, increased through-
out the grazing seasons but the increase
was less or even nonexistent at heavy
grazing.
Critical values of yields, separating
moderate grazing from heavy graxing,
range from 0,6—1,6 tons of dry matter per
hectare varying with site conditions, fer-
tilization and developmental stage of
plants as estimated by their crude protein
content.
Fertilizer applied was 104 N and 24 P (56
P205) kg per hectare on sites with natural
pasture, the sama application for a dry
highland (site 1), dry lowland (site 2) and a
lowland peat soil (site 3). The application
on the grassfield on drained, lowland peat
soilwas 104N,27 Pand61 Kkgperhectare
inlateMayin 1975atsite5,butin 1976and
1977, 100 N, 30 P and 60 K kg per hectare
were applied late in May and 20 kg N early
in August. On the peat soil grassfield on
site 4 the application was 92 N, 25 P and 20
K in the begining of the growth season and
60 N, 13 P and 25 K kg per hectare in late
summer.
Galway 1980-Agr. Inst., Ireland, Rannsókna-
stofnun landbúnaðarins íslandi.
4. Ólafur Guðmundsson, Andrés Arnalds, Björn
Sigurbjörnsson, Sveinn Runólfsson, Halldór Pálsson
ogR.E. Bement( 1978): Experimenton utilization
and conservation of grassland in Iceland. Pro-
ceed. First Int. Rangeland Congress 576-578.
5. Ólafur Guðmundsson, og Sigrún Helgadóttir 1980):
Mixed grazing on lowland bogs in Iceland.
Proceedings Workshop of mixed grazing. Gal-
way 1980: Agr. Inst. Ireland Rannsóknastofnun
landbadbúnaðarins Islandi.
6. Ráðunautafundur 1978 og ráðunautafundur 1981.
Búnaðarfélag íslands og Rannsóknastofnun
landbúnaðarins.