Íslenskar landbúnaðarrannsóknir - 01.09.1982, Page 5

ÍSL. LANDBÚN.
J. AGR. RES. ICEL.
1982 14, 1-2: 3-17
Residue of Linuron in Soils
and Potatoes in Iceland
Derek Mundell
and
SlGURGEIR ÓLAFSSON
The Agricultural Research Institute, Keldnaholt, Reykjavík, Iceland
ABSTRACT
A preliminary investigation was made into the possibility ofaccumulation oflinuron in the soil ofpotato
fields which have been sprayed every spring for up to 15 consecutive years. Levels of linuron were
measured in 32 potato fields sampled in the spring and autumn of 1981. Residue levels were also
measured in the potato samples taken from the same fields.
Linuron levels in sandy soils were low (< 0.6 ppm) after only 3 months following spraying. This level is
compatible with that found by other workers after spraying with orthodox doses of linuron. Levels in
loam soils were, however, considerably higher (mean value of 1.9 ppm in the spring and 2.4 ppm in the
autumn) but this did not have any noticeable effect on the appearance of the potato crops during the year
of this study.
These results indicate that the annual treatment with linuron has not led to residue accumulation in
sandy soils but that the level occurring in loam soils in northern Iceland (2-3 ppm) is so close to the
tolerance limit for the potato crop that there is a considerable likelihood of herbicide toxicity under
conditions which reduce soil residue degradation e.g. a long, cold winter.
Linuron residue levels in the potato samples were similar for both loam and sandy soil cultivation
(0.03-0.05 ppm). This is comparable to levels quoted by other workers and is below the tolerance limits
established by numerous countries.
INTRODUCTION
The potato is the most important vegetable
grown in Iceland. Approximately 800 -
900 hectares are used for potatoes and the
total yield varies between 7000 - 15000
tonnes. This large variation in yield is due
to wide fluctuations in summer tempera-
tures and the length of the growing period,
which is mainly determined by the first
frost in the autumn.
There are mainly 4 types of outdoor
crops grown in Iceland. The most impor-
tant is perennial grass for hay making,
ensilage or for summer grazing. Secondly
there is green forage, e. g. kale, barley and
oats for grazing or ensilage. The third is the
potato and the fourth, rutabagas. Both the
rutabagas and the potatoes are grown by
relatively few specialized farmers of which
some have only a minor income from sheep
or dairy farming. It is clear, therefore, that
the possibilities for crop rotation with other
annual crops are limited. This explains
why there are so many fields in Iceland
where potatoes have been grown for even
30-40 consecutive years. There has,
however, recently been an increasing num-