Íslenskar landbúnaðarrannsóknir - 01.09.1974, Side 37

VORHITI OG VAXTARSKILYRBI NYTJAJURTA 35
ÞAKKARORÐ
Höfundur þakkar Bændaskólanum á Hvann-
eyri og Bútæknideild Rannsóknastofnunar
landbúnaðarins fyrir veitta aðstöðu til vinnslu
efnisins og samningar ritgerðarinnar. Þakkir
skulu einnig færðar Markúsi A. Einarssyni
SUMMARY
Spring temperature and growth conditions
with particular reference to grassland.
Bjarni Guðmundsson
The Agricultural College, Hvanneyri
A study was carried out on changes in air
temperature during the grass- growing season.
The study was based on data from some 40
Meteorological Stations during the period
1931—1960.
It was concluded that the growing season
(spring) will commence when the air tem-
perature first exceeds 4.0 °C calculated on the
basis of monthly averages. According to these
conclusions it seems possible to divide the
country into 4 zones according to the onset
of the growing season.
The onset of the growing season in any
given locality, as defined above, can be esti-
mated with a fair degree of accuracy on the
basis of the latitude and the altitude of the
locality. The onset of the growing season is
delayed by almost 9 days for each of north-
ern latitude and by 3 days for an increase
of 100 m in altitude. The causes of devia-
veðurfræðingi, er las handritið yfir og færði
ýmislegt til betri vegar, dr. Olafi R. Dýr-
mundssyni, sem annaðist gerð hins enska
texta, og öðrum ónefndum, er veittu hug-
myndir, leiðbeiningar og aðstoð.
tions from these norms in different localities
are discussed.
The yearly variation in the onset of the
growing season, expressed as standard devia-
tion, appears to be similar for the various
zones of the country. It was found to have a
mean value of s = * 11.3 days.
The last day in spring with temperature
below freezing point (T<0°C) was found
to be closely related to both the latitude and
the altitude of the locality. Thus the last
day of frost was delayed by almost 10 days
for each degree of northern latitude and by
almost 8 days for an increase of 100 m in
altitude.
Finally there is a discussion on the rela-
tionship between frost- free days (T>0°C)
during the summer and the latitude of the
locality. It was found that the number of
frost- free days decreased by 17 for each de-
gree of northern latitude and by 18 for each
of 100 m. in altitude.
The significance of these findings is dis-
cussed in relation to an assessment of growing
conditions, and the length of the growing
season of forage crops is estimated for the 4
zones of the country as referred to above.