Íslenskar landbúnaðarrannsóknir - 01.09.1970, Qupperneq 69

ÁBURÐARNOTKUN OG VETRARÞOL 67
The experiments were carried out in Mitscherlich pots, which were placed
on tables ca. one nr over tlie earth surface.
In the winter 1968—1969 the soil in the pots was completely icebound, but
may have thawed a little in the many thawing periods during the winter. In
the spring it was obvious that there was an severe winter killing oí the grass
in the pots. The fertilizer effect on the winter liardiness of the grass is the
rnain aspect of the article.
The frost injury is evaluated by a comparison of the yield in 1968 and 1969.
Winter killing was observed were overoptimal amounts of nitrogen were
given and winter killing occurred also at nitrogen shortage. At 120 N, 60 P
and 50 kg/ha there was no injury ancl higliest yield as well for the nitrogen
fronr the compound fertilizer as for nitrogen fronr ammoniumnitrate.
At the lowest phosphorus anrount 13 kg/ha P and where no phosphorus
was given the growth was alnrost completely retarded already in the sowing
year. At tlre phosphorus levels of 26 and 39 kg/ha P tlrere was a severe winter
injury, where the conrpound fertilizer 22-6-9 (22-11-11) was used and where
triple superphosphate with potassium sulphate and anrmoniumnitrate was used,
but there was no injury where the triple superphosphate was used togetlrer
with jrotassium chloride and ammoniumnitrate.
The results of the experinrent with increasing anrounts of potassium show
clearly that potassium increases the frost hardiness of tlre plants.
Yield-increases where snrall from increasing amounts of 22-6-9 (N-P-K) com-
pound fertilizer alone. The phosphorus content of the compound fertilizer is
far too low for the needs of the virgin peat soil used in tlre experiment.
HEIMILDARRIT
AwDONIN, N. S„ 1958: The influence of soil
properties and fertilization on the resist-
ance of winter crops. — A hundred years
of successful fertilizer practice.
Helgason, Bjarni, 1969: Persónuleg heimild.
JÓHANNESSON, Björn, 1961: Unr nýtingu fos-
fóráburðar við grasrækt. Rit Landbúnaðar-
deildar, B-flokkur, 16.
Jung, G. A. og Dale Smith, 1959: Influence
of soil potassium and phosphorous content
on the cold resistance of alfafla. Agr. J.
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rit Rœktunarfélags Norðurlands 64, 65—78.
WlLDING, D. M„ STAHMANN, M. A. Og SmITH,
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