Íslenskar landbúnaðarrannsóknir - 01.09.1977, Side 47

THB INOCULATION OF WHITE CLOVER 45
TABLE 6. MEAN DRY WEIGHT OF PLANTS IN EXPERIMENT 2.
Varieties Bacterial inoculation Lime treatments Lime High lime pellets dressing No lime Means
75 (England) 11.3 10.9 7.7 9.97
83 (Sweden) 20.6 7.6 11.9 13.37
S184 33 (Iceland) 13.1 13.4 9.3 11.93
38 (Iceland) 9.0 13.4 12.0 11.47
No inoculation 15.3 8.8 12.6 12.23
Means 13.86 10.82 10.70
No significant difference No
significant
75 (England) 12.0 9.5 15.1 12.20 difference
83 (Sweden) 11.6 8.5 11.7 10.60
Pajbjerg 33 (Iceland) 10.0 11.0 13.9 11.63
smalbladet 38 (Iceland) 11.2 10.4 9.4 10.33
No inoculation 8.3 12.1 13.6 11.33
Means 10.62 10.30 12.74
No significant difference
DISCUSSION. to be best suited for use as inocula at low
temperatures (Table 2).
This paper outlines the results of a prelimin- Rhizobium strains, which are highly eff-
ary study of natural populations of Rhizob- ective under laboratory conditions, may often
ium trifolii in Iceland where improved ino- not be so when tested in the field. Similarly,
culants ought to be of benefit. Good evid- variation may be seen in some symbiotic
ence of the adaption of Rhizobium strains
from sub-arctic countries to low temperatures
were found. Similar adaptation had previously
been reported by Ek-Jander and Fáhraeus
(1971) after comparing isolates of Rhizobi-
um trifolii from northern Scandinavia with
strains from southern Scandinavia. They
found the northern strains grew faster, nodu-
lated their host plants somewhat earlier and
showed a more vigorous acetylene reduction
than the southern strains when incubated
at 10 °C. It is therefore of considerable
practical importance when white clover
crops are to be cultivated in a cold environ-
ment to use a Rhizobium inoculant adapted
to those conditions.
When both effectiveness and time of
nodulation are looked at together strains 83
from Sweden, 33 and 38 from Iceland seem
associations when exposed to environmental
stress that seem to be equal under optimal
conditions (Pate, 1961). It has even been
found that certain acid tolerant Rhizobium
strains may be relatively poor when tested
under optimal PH conditions, but better than
the other strains when tested under subopti-
mal pH conditions (Lie, 1974). A similar
interaction, although not significant, was
observed in the present investigation, for
strain 26.
The results of Experiment 2 clearly show
the importance of inoculation with Rhizobi-
um bacteria on nodulation. Indigenous bact-
eria were found to be in a low number in
the experimental plots, when estimated by
the M. P. N.-method and by comparing the
numbers of nodules in the uninoculated and
inoculated plots.