THE ANALYSIS OF VIRGIN SOILS. 



361 



The data extant on this subject are rather scanty, and thus 

 far have all been obtained at the California Experiment Sta- 

 cion. 1 But they seem to be very cogent in proving that the 

 growth of crops removed from the soil causes a rapid deple- 

 tion of the nitrogen in the humus-substance, and that so soon 

 as the nitrogen-percentage in the same falls below a certain 

 point, the soil becomes " nitrogen-hungry; " so that the applica- 

 tion of nitrogenous fertilizers is needed and is very effective. 

 The data in the table below, as well as the figure of a culture 

 experiment ( Xo. 52 below), illustrate this point. 



ADEQUACY AND INADEQUACY OK XITKOUKX CONTEXTS OK HTMt'S. 



Nos. 6 and 1679 show the usual humus- and nitrogen-percentages in 

 the "black adobe" or "prairie" soils of California. Xos. 1842 and 

 1-^41 represent the same soil as 1679, upon which, however, ramie and 

 ray grass had respectively been growing, without fertilization, for about 

 ten years ; showing that while the humus-content of the soil has /;/r/vw.\vv/, 

 the nitrogen-content of the hinnns //</. dt-crcascJ in the case of ramie by 

 72.78^', in that of the grass by 76.78',,' ; reducing the land to figures 

 commonly found in the humid region. In the case of the ramie, the 

 partial return through the leaves has resulted in a higher humus-content, 



1 The Supply ef Si'il A'r/nw/i, Krp. Cal. l-'.xpt. Station, iS<)j-<r,. page 6S ; ibid., 

 894-95, page 28; 7"ic- Ri-ci'^iiitii'H ,>/' A'itr; ;;',-// Hnn^riucss in .S'i'/.V, in Mull. 47, l>iv. 

 of Chemistry, U.S. Department of Agriculture, i8<);; I.aiuUv. Pressc, Xo. ; 5, July 

 188^. See also for detailed data chapter 8, page 13;. 



- Calculated upon the true humus substance imatiere noire), //<'/ by detei mining 

 total (incl. unhumified) nitrogen in the soil. 



