Íslenskar landbúnaðarrannsóknir - 01.09.1977, Side 48

46 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
The small nodules found in the uninocul-
ated contröls were most probably caused by
a small population of ineffective Rhizobium
bacteria. This population was too small to
be detected by the M. P. N. -method.
Seed pelleting and inoculation with an
effective strain of Rhizobium has been found
to be most advantageous in upland reclama-
tion in Wales where the establishment of
white clover is limited by the low numbers of
indigenous nodule bacteria and the acidity
of the soil (Jones, 1966; Jones and
Thomas, 1966; Jones, Druce and Will-
IAMS, 1967). The pH of upland soils in
Wales is rather low, often between pH 4.0
and 4.5, whereas the pH of the untreated ex-
perimental plots in Iceland was between
5.7 and 5.9. It would therefore not be expect-
ed that lime pelleting or conventional lime
spreading would have the same effect in
Iceland as in countries with more acid soiis
and, in fact, none of the lime treatments
affected nodulation or yield of dry matter.
The fact that the observed responses to
inoculation in terms of nodule production
were not translated to differences in plant
growth may be due to the lack of adaptation
to Icelandic conditions by the two varieties
used which may have resulted in a reduction
in the amounts of nitrogen fixed in the nod-
ules or by a reduction in the ability of the
plants to assimilate any fixed nitrogen. Alt-
hough there were significant differences
between treatments, the number of nodules
in each treatment was very low. This low
number of nodules could álso account for
the lack of effect on growth.
The two varieties, Aberystwyth S184, a
small leaved variety, and Paibjerg smalblad-
et, a medium small leaved variety from Den-
mark, were both thought to be suitable for
using in cold conditions but neither of them
survived their first Icelandic winter. It is
apparent that the type of screening for
bacterial strains carried out in the present
experiment must be paralleled by the breed-
er who must select more hardy types, possibly
from within Icelandic ecotypes, that can fix
nitrogen at low temperatures.
ACKNOWLEDGEMENTS
The authors would like to acknowledge and
thank Dr. Bjarni Helgason, for chemical
analysis of soil samples and for his stimulat-
ing interest in this investigation, to Dr. A.
Durrant, for helpful advice on the stat-
istical analysis of the data, and to Sverrir
Hardarson, for technical assistance.
The financial support of the Icelandic
Scientific Foundation (Vísindasjóður) is
gratefully acknowledged by one of us (G. H.).