TOXICITY STUDIES WITH DICYANODIAMIDE ON PLANTS 1 
By F. E. Allison, Biochemist, Fixed Nitrogen Research Laboratory, J. J. Skinner, 
Biochemist, and F. R. Reid, Assistant Biochemist, Soil-Fertility Investigations, 
Bureau of Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The conclusions reached from the ex¬ 
perimental work dealing with the effect 
of dicyanodiamide on plant growth 
which have been reported by various 
investigators vary widely. In some 
instances the compound has been re¬ 
ported as very toxic to plants, in others 
as merely unavailable as a nitrogen 
source for plants, and practically inert. 
At the Fixed Nitrogen Research Lab¬ 
oratory of the United States Depart¬ 
ment of Agriculture as well as elsewhere, 
experiments have shown that small 
quantities of dicyanodiamide prevent 
nitrification in the soil. It seemed, 
therefore, that possibly the bad effects 
of the compound might be due to the 
fact that in its presence the soil nitro¬ 
gen is not converted into nitrates or at 
least is converted so slowly that plants 
undergo nitrate starvation. Thus dicy¬ 
anodiamide would act as an indirect 
rather than direct poison to plants. The 
experiments reported here were planned 
to determine this point by studying the 
growth of plants in soils containing 
dicyanodiamide and varying quantities 
of sodium nitrate. 
SOILS AND PLANTS USED IN THE 
EXPERIMENTS 
The soils used were Norfolk sandy 
loam, a Coastal Plain soil obtained from 
near Norfolk, Va., and Chester loam, a 
Piedmont Plateau soil secured from 
near McLean, Va. The plants used 
were wheat and cowpeas. 
SOIL PREPARATION AND 
FERTILIZATION 
The materials to be tested were 
thoroughly mixed with each 10-pound 
portion of sieved soil and put into 
1-gallon glazed pots and planted, each 
treatment being in duplicate. After 
germination was complete the plants 
were thinned to 10 and 5, respectively, 
for wheat and cowpeas. 
All pots except those designated as 
“no fertilizer 77 received 80 pounds of 
P 2 0 5 and 40 pounds of K 2 0 per acre in 
the form of monocalcium phosphate 
and potassium sulphate, respectively. 
The calculations were based on 2,000,000 
pounds of soil per acre to a depth of 6 
inches. The sodium nitrate and di¬ 
cyanodiamide were applied at various 
rates and in varying proportions. 
Check pots were included in which the 
normal applications of phosphate and 
potash were made, but no nitrogen. 
In the tables which follow, the term 
fertilizer ratio refers to the ratio of 
NH 3 , P 2 0 5 , and K 2 0 in the order named. 
DURATION OF EXPERIMENTS 
The wheat was planted on March 18, 
1922, and cut on May 1, 1922. During 
this period the pots were weighed at 
frequent intervals and the water lost 
by evaporation restored. The wheat 
was harvested sooner than desired be¬ 
cause of an unusually severe attack of 
mildew. 
The cowpeas were planted on May 
16, 1922, and cut on June 21, 1922. 
The excessive heat in the greenhouse 
was causing many of the lower leaves 
to drop, making necessary the early 
termination of the experiment. 
EXPERIMENTAL RESULTS 
First Experiment 
RESULTS WITH WHEAT 
A. Sodium Nitrate Constant, 
Dicyanodiamide Variable 
The results from pots of wheat 
treated with varying quantities of 
dicyanodiamide, together with a con¬ 
stant and adequate nitrate supply, 
are given in Table I and Figure 1. 
Tests were also included using sodium 
nitrate and dicyanodiamide singly for 
comparison. 
1 Received for publication June 5, 1924; issued May, 1925. The experiments herein reported were 
conducted at Arlington, Va., the Soil Fertility greenhouses being used. 
Journal of Agricultural Research. 
Washington, D. C. 
( 419 ) 
Vol. XXX, No. 5 
Mar. 1,1925 
Key No. R-4 
