Rit Landbúnaðardeildar : A-flokkur - 01.05.1967, Side 182

that, wlien using 70 kg/ha of „KJARNI“ (NH4NÖ3) and no pliosphor,
the amount of phosphor in the yield comes to a min. in 10—15 years.
At Akureyri 51 kg/ha P2O5 gave an increase in yield of 22.9 hkg/ha
and at Sámsstaðir the increase for 60 kg/ha was 28.5 hkg/ha.
The minimum amount of P in grass is found to be approx 0.12% of
the dry matter, the average being approx 0.30%. When the lack of P
begins to control the yield, vegitation changes. Seeding grass i. e. Timothy
and Alopecurs pratense, gradually disappears and Festuca rubra, Poa
pratensis, Agrostis and Deschampsia take its place.
At Hvanneyri the peat soil is so low in P, that there is no growth. For
this kind of soil and silt loam, 60 kg/ha P2O5 give good results with 120
kg/ha of N-fertilizer.
The spring is to be prefered to the autumn for spreading of P-fertilizer.
When spreading P-fertilizer for the first time in large doses, no difference
was found weather the fertilizer was spread on the surface after seeding
or before rotavation.
2. In most cases 80 kg/ha K^O and 120 kg/ha N was found to be
sufficient. The increase in yield for this dose of potash (K^O) was 10—12
hkg/ha of hay. With increasing doses of potash the percentage of potassium
in the vield increases but Ca, Mg and Na deerease at the same time.
No appreciable increase in yield was found when using K2SO4 in
romparison with KCl. In this trial two doses, 60 and 120 kg/ha KoO were
used with 120 kg/ha N-fertilizer.
3. Trials with 3 different doses of NH4NO3 i. e. 40 — 80 — 120
kg/ha N with 60 kg P2O5 and 75 kg K^O as basic fertilizer, have given
16—27 and 35 hkg/ha respectively as increase in yield of hay.
White clover does not survive in a hayfield which receives 80 kg/ha
N-íertilizer or more over some years. Comparison of the three types of
N-fertilizer — „Kjarni“ 33.5% N, Calsium nitrate 15.5 N (Ca(N0g)2
28% CaO) and (NH^^SO^, 20.5 N, gave the respective yield values
100 — 98 ■— 90. The above are average figures for 11—20 years.
Ca(NO;3)2 increases the amount of Ca in the yield considerably. In a
few years the (NH4) 2SO4 decreases the pH of the soil from 6.2—4.8 and
vegitation changes. Seeding grass i. e. Timothy and Fox tail gradually dis-
sappears and Poa pratensis, Agrostis, Deschampsia take its place. Twenty
years of trials with „Kjarni“ show very little decrease in pH and no
change in vegitation.
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