Rit Landbúnaðardeildar : B-flokkur - 01.12.1961, Qupperneq 33

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of radioactive phosphorus. On the average this percentage ranged from 50 to 55 for both of
the soils and bears no apparent relationship to the rate of phosphorus application.
The last column lists the per cent of the applied phosphorus taken up by the green parts of
the grass during the season of application. The smallest dose was utilized most efficiently.
The phosphorus uptake on different soils.
In the tests, the results of which are outlined in Table 3, the fertilizer treatments were identical
for all pots. One kind of silt loam and peat soils from three Iocations, with and without lime
additions, were included in the study; thus seven „kinds“ of soils were dealt with.
The following comments relating to Table 3 seem appropriate:
1) The effects of lime on yield and calcium and phosphorus contents of the grass have been
outlined previously (Jóhannesson. 1960). The experimental results of 1960 were in line with the
conclusions reached in the mentioned paper. These conclusions may be summarized as follows:
For the peat soil from Olfus, lime gave large yield response in the first experimental season
and significantly increased yield in the second year; the yield increase was indeterminate or in-
significant in the third, fourth and seventh year, while statistically significant in the fifth and
sixth year. For the peat soil from Hvanneyri, the yield increase due to liming has been highly
significant for the last three experimental seasons, while such increase was not statistically signi-
ficant for the first three years. For the peat from Ytri-Hólmur no yield response from liming
has been observed. It is noteworthy that the three peat soils in question responded differently
to liming.
2) The pots containing the peat from Hvanneyri gave significantlv higher yields than the other
pots, the yields of which were of similar order of magnitude (column No. 1).
3) The phosphorus content of the grass for each particular treatment showed considerable
seasonal variation (column No. 2). The effect of Iime on the phosphorus content of grass was
not measurable, neither in these nor in Icelandic field trials (Jóhannesson, 1960). On the
average the phosphorus content of the grass grown in the peat soils was of similar magnitude,
while it was a little lower for the grass of the silt loam pots.
4) The total uptake of phosphorus by the grass followed the same trend as the yield (co-
lumn No. 3). The highest uptake was observed for the peat from Hvanneyri, being greatest
for the limed pots. The limed peat from Olfus supplied more phosphorus to the grass than
the unlimed soil as long as the lime increased yield. The phosphorus uptake for the silt loam
soil was somewhat less than for the peat soils.
5) The „apparent phosphorus balance“ of the pots dealt with in Table 3 was equal to the
total phosphorus uptake times a constant factor, 100/124,2. The comments on the phosphorus
uptake under 4) therefore also hold for the „apparent phosphorus balance" listed in column
No. 4.
6) Column No. 5 supplies the following information: For the silt loam and peat soils from
Ölfus and Ytri-Hólmur, on the average, 55 to 60 per cent of the total phosphorus taken up
by the grass came from the same season’s fertilizer application, while the remainder came
from soil phosphorus. For the Hvanneyri peat soil, on the average, about 67 per cent or %
of the phosphorus taken up by the grass came from the fertiliizer and 'A from the soil. Marked
seasonal variations were observed regarding the fertilizer phosphorus utilization.
7) The last column (No. 6) lists the per cent of phosphorus fertilizer taken up during the
season of application. The fertilizer applied to the Hvanneyri peat was utilized most effici-
ently in the year of application, the grass taking up, on the average, 18 and 21 per cent for
unlimed and limed soil, respectively. The fertilizer utilization was poorest for the silt loam soil.