Rit Landbúnaðardeildar : B-flokkur - 01.12.1961, Síða 51

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(ammonium nitrate) on the nitrate content of the hay crop of tuns. Tables 4 and 5 list the
nitrate content of grass at different times, when large quantities of ammonium nitrate are
applied in one application to tuns. The graph in figure 1 presents a summary of most of the
data in tables 4 and 5, and those of the first cutting presented in table 3. The mean figures
listed in the last lines of tables 4 and S are used for the graph. On the graph are also plotted
data presented in table 8, showing effects of fertilizer nitrogen on the nitrate content of Brass-
ica oleracea ace-phala', the nitrate content in the sample that received 150 kg N/ha is abnorm-
ally low, as is indicated by two other analyses of this plant presented in table 8. Table 6 illu-
strates that the initial effect of a nitrogen fertilizer application on the nitrate content of grass
gradually falls off with time. This is also illustrated by table 7 which lists a number of nitrate
determinations on grass samples from experimental pasture plots. These data indicate that
the effect of a second application of 100 kg N/ha as ammonium nitrate on the nitrate content
is greater than that from an identical quantity applied at the beginning of the growing season.
The high nitrate contents of samples from plots B 1—3 are assumingly due to rahter dense
admixture in the vegetative cover of Achilléa Millefolium. Table 8 lists a few nitrate data
for fodder plants of the Brassica family. These data are in line with the known fact that plants
of this family are higher in nitrates than grasses (Gramineae) for similar environment and fer-
tilizer treatments.
The practical conclusions drawn from the present study are as follows:
1) For permanent grassland (tuns) it is recommended to avoid higher annual applications
than 120 kg N per hectare to safeguard against nitrate poisoning of live-stock.
2) For Brassica species the rate of application should not exeed 150 kg N per hectare.
This quantity will, however, cause a rather high nitrate content of the herbage, but
particularly in cool seasons satisfactory yields of the crops in question will not be ob-
tained, unless rather heavy applications are practiced.
ÞAKKARORÐ
Kristinn Jónsson, ráðunautur á Selfossi, og Guðmundur Egilsson, starfs-
maður við tilraunastöðina á Varmá, báru vaxandi magn köfnunarefnis á
grasreiti og skáru upp á mismunandi tímum sérstaklega vegna rannsókna á
nítrati. Var tilraunin á Varmá framkvæmd í samráði við dr. Sturlu Friðriks
son. Hin mörgu sýnishorn af beitarreitum á Laugardælum voru og sumpart
tekin vegna þessara rannsókna. Sýnishorn frá tilraunastöðvum jarðrcektarinnar
voru valin úr fjölda sýnishorna, er stöðvarnar senda árlega til efnarannsókna.
Anna Ólafsdóttir ákvarðaði nítrat í grassýnishornunum.
Það fólk og þær stofnanir, er að ofan greinir, á skyldar þakkir fyrir áhuga
þeirra, dugnað og ágætlega unnin störf.
HEIMILDARRIT
Bradley, W. B., Eppson, H. F. og Beath, 0. A., 1940. Livestock poisoning by oat hay and
other plants containing nitrate. Wyoming Agr. Exp. Sta. Bull. 241.