Mar. 1,1925 
Toxicity Studies with Dicyanodiamide on Plants 
423 
Table IV.— Green weight of cowpeas grown after wheat without additional fertiliza¬ 
tion 
NORFOLK SANDY LOAM 
Source of nitrogen • 
Fertilizer 
ratio 
Green 
weight 
Average 
Increase 
or 
decrease 
over 
check 
Nodule 
formation 
No nitrogen___ __ _ 
0-8-4 
Grams 
/ 26.0 
\ 25.2 
/Abundant 
\ Do. 
/ Do. 
\ Do. 
/Many. 
\ Do. 
f Do. 
\Abundant. 
Sodium nitrate 40__ _ 
4-8-4 
\ 24.3 
/ 25.4 
1 25.4 
/ 20.6 
} 25.4 
0.2 
Dicyanodiamide 40__ 
4-8-4 
} 18.0 
—7.2 
Dicyanodiamide 40, sodium nitrate 40.. 
8-8-4 
\ 15.3 
/ 18.3 
} 17.5 
-7.7 
\ 16.6 
CHESTER LOAM 
No nitrogen-- 
Sodium nitrate 40_ 
Dicyanodiamide 40.... 
Dicyanodiamide 40, sodium nitrate 40.... 
0-8-4 
/ 35.6 
\ 35.1 
} 35.4 
4-8-4 
/ 40.3 
\ 39.9 
} 40.1 
4.7 
4-8-4 
/ 38.7 
\ 36.0 
} 37.4 
2.0 
8-8-4 
/ 31.2 
\ 34.1 
} 32.7 
-2.7 
/Few. 
\ Do. 
/Many. 
\Few. 
/ Do. 
\None. 
/Few. 
\ Do. 
• The figures in this column refer to the quantities of nitrogen applied to the crop of wheat, previously 
grown in this soil. 
In Table IV, as well as in those which 
follow, a column is included showing 
the relative abundance of nodules. No 
doubt the abundance of nodules on the 
plants in some pots, especially in those 
containing the Norfolk soil, was quite 
a factor in determining growth. 
Second Experiment 
EFFECT OF VARIOUS AMOUNTS OF DI¬ 
CYANODIAMIDE WITH AND WITHOUT 
SODIUM NITRATE ON COWPEAS 
At the same time that the experi¬ 
ments with cowpeas reported on above 
were begun, another series was also in¬ 
cluded to determine the toxicity of 
dicyanodiamide to cowpeas and the re¬ 
lation of the nitrate supply to the in¬ 
jury. The results are given in Tables 
V and VI and illustrated in Figures 2 
and 3. Plates 1 and 2 show the plants 
just prior to harvesting. 
The results reported in Table V with 
the Norfolk sandy loam were somewhat 
unexpected. The soil which grew such 
a poor crop of wheat in the absence of a 
nitrogenous fertilizer showed negligible 
responses to sodium nitrate with cow¬ 
peas. Furthermore, small applications 
of dicyanodiamide depressed the yield 
quite markedly, while the larger quan¬ 
tities injured germination and practi¬ 
cally killed the plants which did appear 
above the surface. In these extreme 
cases, the roots became brown and 
rotted. The use of sodium nitrate with 
the dicyanodiamide increased the in¬ 
jury up to 20 pounds of ammonia per 
acre and decreased it slightly there¬ 
after. These results are decidedly dif¬ 
ferent from those obtained with wheat* 
The data for the Chester loam show a 
fair increase in green weight of the 
plants resulting from the use of 
sodium nitrate alone. Dicyanodiamide 
depressed the yields at 20 pounds of 
ammonia per acre and above. Where 
sodium nitrate was used with the 
dicyanodiamide the injury by the 
latter was partially overcome. The 
results obtained with cowpeas on this 
soil agreed more nearly with those 
obtained with wheat than was true 
with the lighter soil experiments. 
Nevertheless, the dicyanodiamide in¬ 
jury was greater for cowpeas than for 
wheat, as shown both by green weights 
and the yellowing and mosaic effects 
on the leaves. 
