Fjölrit RALA - 15.12.2000, Blaðsíða 33

31
The inclusion of precipitation in the model was also tested but was not found to be
significant. The development of the two timothy varieties, Vega and Engmo, was quite similar
so their average was used in the analysis. The P. pratensis varieties were analyzed separately.
Coefficients for regression on temperature are shown in Table 32. This model explained 21%
of the total variation for timothy, 10% for Fylking, 31% for Lavang and 18% for Seida.
Table 32. Coefficients for temperature effects on digestibility.
Coeffícient SE
Lavang 0.027 0.023
Fylking 0.020 0.024
Seida -0.002 0.018
Timothy 0.048 0.016
The coefficients for decline in digestibility of timothy was 0.048 (SE=0.016). For a 1
degree (”C) increase in temperature, the rate of decline in digestibility increases by 0.048
percent units day"1. This is precisely the same coeffícient as found earlier in material ffom
Sweden (Thorvaldsson, 1987; Thorvaldsson and Fagerberg, 1988; Thorvaldsson, 1992). This
result was obtained at lower temperatures than in Sweden, indicating linearity of temperature
eífects from very low temperatures up to temperatures between 20 and 30°C. The average
decline of digestibility during the harvest period was 0.24 percent units day'1 and during that
time the average temperature was 9.4°C. Extrapolation of the regression equation indicates a
zero decline of digestibility of timothy around 4.5°C.
No significant effects of temperature on digestibility of P. pratensis and A. pratensis
were found. This results could be because of less accuracy in the estimate of digestibility as for
timothy an average of two varieties was used. It could also mean that decline of digestibility in
these species is less dependent on temperature than in timothy.
Minerals
The content of minerals (% DM) was measured for tlrree harvest dates in 1996. The results are
shown in Tables 33-36.
Locations. Phosphorus content in grass was lowest in Korpa, and potassium content was
lowest in Upemaviarsuk. It has earlier been mentioned that the soil analysis was carried out on
the stone-free material in Upemaviarsuk and the soil there is very stony. There was no clear
difference between locations in magnesium content. Calcium content was highest in the grass
in Kollafjorður and so was the soil pH. Sodium content was much higher in the Faroe Islands
than at the other locations. This can be explained by the short distance to the sea together with
heavy winds. Sometimes salt causes damage to potatoes in Kollafjorður.
Titne. Phosphorus content decreased during the harvest time as well as the potassium content.
According to the literature, decline of the content of these minerals during the growth period is
natural (Knauer 1970; Óskarsson and Gudmundsson, 1971). Magnesium, calcium and sodium
content did not change much during the growth period. Results from the literature vary for
these minerals; they either increase, decrease or remain at the same level (Thorsteinsson and
Ólafsson 1965; Eaton and Meehan 1971).