358 SOILS. 



cannot, of course, afford even an approximation to the nitn> 

 gen-content ; except that as in the humid region, the nitrogen- 

 percentage, is not known to exceed about 5 or 5.5%, an ap- 

 proximate estimate can be made on that basis. In the arid 

 region, according to location, the nitrogen-percentage may be 

 from three to six times greater for a similar amount of humus. 

 (See chap. 8, p. 135). In the writer's experience, a nitro- 

 gen-percentage of.i% in the arid region is a very satisfactory 

 figure, indicating that the need of nitrogen-fertilization is not 

 likely to arise for a number of years. 



Nitrification of the Organic Matter of the Soil. In order to test the 

 question whether or not the nitrogen of the unhumified debris existing 

 in surface soils is directly nitrifiable, the writer selected a soil which in 

 its natural condition sustains intense nitrification, so that at some points 

 it contains as much as 1200 pounds of sodic nitrate per acre. The 

 composition of this soil, representing the land of the "ten-acre tract" 

 of the southern California sub-station, is as follows : 



SOIL FROM "TEN-ACRE TRACT," SOUTHERN CALIFORNIA SUB-STATION, NO. 1284. 



Coarse Materials > o.55 mm i.oo 



Fine Earth 99.00 



100.00 



CHEMICAL ANALYSIS OF FINE EARTH. 



Insoluble matter 62.62 \ 



Soluble silica ... 8.30 j 7 ' 92 



Potash (K 2 O) .95 



Soda (Na 2 O) .50 



Lime (CaO) 5.07 



Magnesia (MgO) ... .84 



Br. ox. of Manganese (MnsO*) .06 



Peroxid of Iron (FeaOa) 6.43 



Alumina (A1,O 3 ) 3.88 



Phosphoric acid (PaOs) .21 



Sulfuric acid (SO 3 ) 06 



Carbonic acid (C O 2 ) 3.66 



Water and organic matter 6.02 



Total 99-7 



Water-soluble matter, percent .137 



Sodic nitrate, per cent .020 



Humus 1 .99 



" Ash 1.13 



" Nitrogen, per cent, in Humus 10.30 



" " , per cent, in soil .203 



Total Nitrogen in soil 330 



" in unhumified matter .127 



Available Potash j citric ) 



Available Phosphoric acid \ method ) 



Hygroscopic Moisture 5.81 



absorbed at 15 C. 



