Food for Plants. 151 



comparison is made of the materials mentioned in the 

 title of this paper would seem to justify the publication 

 at this time of a brief summary of the work. A detailed 

 account covering- the first 15 years of this work has 

 already been published (3). Much of this need not be 

 repeated, but the results of the last 5 years are of value 

 as confirming the earlier work. 



Experimental. 



The work was originally outlined under the l)road 

 heading " Investigations Relative to the Use of Nitro- 

 genous Materials," and this included: (a) a determina- 

 tion of the yield of dry matter and nitrogen in crops 

 from soils receiving various treatments under controlled 

 conditions; (b) the percentage of nitrogen in the crop 

 as affected by the treatment; (c) the utilization of nitro- 

 gen in different materials; (d) the relative efficiency of 

 nitrogen in different materials; (e) the residual effects 

 of nitrogenous substances; (f) denitrification and (g) 

 the effect of special treatment on the income and outgo 

 of nitrogen in the soil. 



As the work has progressed, more and more attention 

 has been given to the utilization and relative efficiency 

 of nitrogen in different materials, and it is this phase of 

 the work which is to receive consideration in this paper. 



In order that the work might be under more perfect 

 control, it was carried out in galvanized iron cylinders, 

 open at both ends and ha\dng a diameter of 231^ inches 

 and a depth of 4 feet. These cylinders were set on the 

 ground so that about 2 inches remained above the ground 



& 



?^^ 



level. Thus the contents of the cyhnders are isolated so 

 that the roots of the crops growing in them are prevented 

 from getting mineral plant-food from outside sources. 

 The sub-soil is a gravelly sandy material such as occurs 

 where the cylinders are located, but the top soil is n 

 loam (Penn loam) brought from another source, an 

 8-inch layer of which was placed in each cylinder on top 

 of the subsoil, each cylinder receiving the same weight 

 of the thoroughly mixed soil. 



