ATMOSPHERIC-NITROGEN FERTILIZERS. 39 
At the smallest rate most of the nitrogen was utilized for stalk produc- 
tion rather than grain. The probable causes for this are the same as 
previously stated in connection with other plats. Under the con- 
ditions of this test cyanamid produced just as satisfactory early 
effects and also gave as good increases in yields as could be expected 
from any fertilizer. 
REVIEW OF THE RESULTS. 
An examination of the results here reported shows that with the 
exception of cyanamid all of the nitrogen materials tested gave 
responses quite similar to those from ammonium sulphate and 
sodium nitrate. It should be pointed out, however, that some of 
the materials, especially Urephos, were not tested on a sufficiently 
large number of plats to show clearly their relative values, but never- 
theless, under the conditions of the test cyanamid was the only 
fertilizer which in some instances gave very erratic results. Because 
of the erratic results obtained with cyanamid and the unusual in- 
terest attached to this material as one of the important synthetic 
sources of nitrogen, special consideration of it seems desirable. In the 
following discussion the various phases of cyanamid fertilization will 
be considered, both from the standpoint of the present study and in 
the light of results reported by other investigators. 
The importance of avoiding the use of cyanamid in large propor- 
tions in fertilizer mixtures containing acid materials has been em- 
phasized. Where large amounts of cyanamid were mixed with acid 
phosphate the growth and yields of the various crops were poor. 
This was due to the polymerization of a portion of the cyanamid nitro- 
gen to dicyanodiamid, which is not only unavailable as a fertilizer 
but also toxic for some plants. When cyanamid and acid phosphate 
were applied separately the undesirable changes were avoided; like- 
wise in the case of mixtures containing basic phosphates. It is 
customary in American fertilizer practice to use not to exceed 60 
pounds of cyanamid per 1,000 pounds of acid phosphate in mixed 
fertilizers. While under such conditions a small amount of dicyano- 
diamid may^ be formed, the quantity is not sufficient to be par- 
ticularly objectionable and the mechanical condition of the mixture 
is considerably improved. 
The method of using cyanamid in the field is very important. In 
the experimental work at Muscle Shoals the conditions of use adopted 
were made to conform as nearly as possible to American agricultural 
practice. This fact needs to be especially emphasized, since in many 
cases it largely explains the poor results with cyanamid. The main 
factors, namely, soils, crops, and time and methods of application 
deserve special mention. 
The soils which are usually considered most suitable for cyanamid 
fertilization are those in best tilth, neutral, and having high nitrifying 
efficiencies. Those which are not suitable are acid soils, very sandy 
soils, acid humus soils, and very heavy plastic clays. A good supply 
of colloids and organic matter is also considered desirable; likewise a 
high absorptive capacity provided the aeration is adequate. The 
soils used for the experiments here reported were loams and therefore 
apparently satisfactory. However, all of the soil types were slightly 
acid and some of them poorly aerated, especially on fields 2 and 3. 
The nitrifying powers were likewise low, as shown by laboratory 
