ATMOSPHERIC-NITROGEX FERTILIZERS. 43 
Urea seemed to be as readily available as sodium nitrate and 
equally as good in all respects as any other material used. Since 
urea is an excellent material physically and leaves neither a basic nor 
acid residue in the soil it should prove to be an almost ideal nitrogen 
carrier for all types of soils. 
Urephos gave somewhat variable results, due to the wide soil 
variations, the yields being especially good with wheat but much 
poorer with rye. The limited use of the material does not justify 
conclusions as to its value. 
It should be noted that nearly all the fertilizer materials tested 
have a much higher plant-food content than those now commonly 
employed. While some of these materials are suitable for direct use 
in mixed fertilizers, others will require some modifications of present- 
day fertilizer practice, owing to their physical condition. 
The results as a whole may be summed up by the statement that 
under the conditions of these experiments all of the nitrogen mate- 
rials tested with the exception of cyanamid were of about the same 
value as sodium nitrate and ammonium sulphate. With regard to 
the latter two materials, if there was any difference between them it 
was slightly in favor of ammonium sulphate. Further experimenta- 
tion is necessary, however, to establish more definitely the relative 
values of all of these materials and to determine the conditions under 
which they can be most advantageously used. Such experimenta- 
tion is now in progress by the Office of Soil-Fertility Investigations. 
It is hoped, however, that similar studies will be undertaken by 
others, since atmospheric-nitrogen products are becoming increas- 
ingly important in supplying the needs of agriculture. 
