Mar. 1, 1925 
427 
Toxicity Studies with Dicyanodiamide on Plants 
plants 17 per cent on the Norfolk 
sandy loam and 13 per cent on the 
Chester loam. In the presence of 
sodium nitrate dicyanodiamide pro¬ 
duced the tip burning but did not 
markedly decrease the value of sodium 
nitrate. This indicates that dicyano¬ 
diamide is not a marked direct poison 
for wheat but is merely unavailable as 
a plant food and probably prevents the 
proper utilization of the soil nitrogen. 
Experiments to determine the resid¬ 
ual effects of dicyanodiamide showed 
that the material remained in the pots 
and produced a marked decrease in the 
second crop (cowpeas) on the sandy 
soil whether previously used with or 
without sodium nitrate. On the loam 
soil the residual effects were almost 
negligible. 
Additional experiments where cow- 
peas were grown in the presence of fresh 
iS.A/. O & /O 20 40 80 /O 20 40 SO 
z/zi/^cS' 7yy&o<z/<9/s f- 
/vo aa/y-j&o&jeya 
Fig. 3—Diagram showing the yield of eowpeas from pots receiving various amounts of dicyanodiam¬ 
ide and sodium nitrate 
In the presence of 40 pounds of 
ammonia as dicyanodiamide, sodium 
nitrate equivalent to 5 pounds of 
ammonia on the lighter soil and 10 
pounds on the heavier was sufficient to 
counteract the decrease in the green 
weights of the wheat plants produced 
by the dicyanodiamide. Where sodi¬ 
um nitrate and dicyanodiamide were 
used in varying proportions, the green 
weights depended primarily upon the 
nitrate supply, the dicyanodiamide 
exerting only a slight injury and its 
nitrogen being unavailable. 
applications of dicyanodiamide showed 
that this plant is injured even by small 
applications of the material (5 pounds 
of ammonia per acre). Sodium nitrate 
usually did not counteract the injury 
and even increased it in several in¬ 
stances. Practically all plants grown in 
the presence or absence of nitrate nitro¬ 
gen showed a yellowing of the lower 
leaves and a slight mosaic appearance of 
the others. With the larger applications 
on the sandy soil germination was 
affected and the plants were nearly dead 
when the experiment was terminated. 
