Íslenskar landbúnaðarrannsóknir - 01.09.1975, Side 20

18 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
borin þessi tvö ár, 1963 og 1973. Á Sáms-
stöðum er stærri Kjarnaskammturinn meiri
en venjulegur túnskammmr, 180 kg N/ha.
Afleiðangarnar eru veruleg rýrnun katjón-
anna Ca-J-Mg-f-K, sem minnka dr 10,3 m.e.
niður í 6,3 m.e. Þetta jafngildir því, að
mettun jónrýmdarinnar hafi fallið úr um 20
af hundraði niður í 12 af hundraði á þessu
10 ára tímabili.
Samkvæmt erlendum rannsóknum má gera
ráð fyrir óæskilega miklum áhrifum járns og
áls og jafnvel beinum Ca-skorti fyrir að-
fluttan gróður, ef Ca-mettun jónrýmdarinnar
fellur langt niður fyrir 20—25 af hundraði
SUMMARY
Changes in hase status and soil organic
matter content resulting from long-term use
of three different nitrogen fertilizers
Bjarni Helgason
Agricultural Research lnstitute,
Reykjavík, Iceland.
20—25 years of continuous use of ammoni-
um nitrate, ammonium sulphate and calcium
nitrate at four experimental stations has re-
sulted in significant changes in soil pH, ex-
changeble Ca++, Mg++ and K+ and also
in minor changes in soil organic matter con-
tent.
The experimental sites are in south of
Iceland at Sámsstaðir where it is located on
a freely drained slightly sloping soil with a
cation exchange capacity (CEC) of 52 m.e/
100 g, and at Akureyri in the North, where
the site is imperfectly drained mineral soil
(CEC = 60.9 m.e.), at Reykhólar in the
western part of the country on a reclaimed
peat (CEC = 69-9 m.e.) and in the East the
site is at Skriðuklaustur on a reclaimed but
imperfectly drained peat (CEC= 60.9 m.e.).
(Coleman, Kamprath og Weed 1958),
(Jackson 1967). Þetta mettunarhlutfall er
talið þurfa að vera enn meira, eftir því sem
jarðvegur verður snauðari að lífrænum efnum
og leirkenndari, en þó breytilegur eftir því,
um hvaða leirtegund er að ræða í jarðvegin-
um (Coleman, Kamprath og Weed
1958). Með hliðsjón af þessu og því, hve
heildarmettunarhlutfall (Ca-f-Mg-j-K) hefur
minnkað í sumum tilraunaliðum, sem hér
hefur verið fjallað um, má kannski ætla, að
sú stund kunni að renna upp, fyrr en varir,
a. m. k. sumsstaðar, að notkun kalks komi til
álita sem reglubundinn þáttur í ræktun.
Changes are largely restricted to the top
soil (0—5) and seem to disappear in the
10—15 cm soil depth as compared to the
reference plots of no-nitrogen (Tables I, II
& II A).
Severe leaching due to ammonium sulp-
hate has for instance resulted in Ca+ + falling
from 12.7 m.e. to 2.4 m.e. at Sámsstaðir and
from 16.3 m.e. to 3.8 m.e. at Reykhólar.
Corresponding decrease in pH is from 5.9 to
4.8 at the former and from 5.1 to 4.3 at the
latter station. On the sites at Akureyri and
Sámsstaðir the pH has remained constant
about 4.8 for a period of at least 10 years
thus indicating the strong buffering effects
within these soils (Table I).
On the other hand the continuous use of
calcium nitrate has led to a considerable
increase in Ca++, even twice the quantity
of the reference plots, esperially where net
precipitation is lowest. A corresponding in-
crease in soil pH will result. However, in the
reference plots it is clear that changes in pH
follow the quantity of organic matter, e.g.
pH increases with lowering of organic matter
which in mrn lowers with soil depth.