262 University of California Publications in Agricultural Sciences [Vol. 1 



38,000 pounds of organic nitrogen distributed through the depth 

 of twelve feet. 



HUMUS IN SOILS OF DIFFERENT TEXTURE 



We have grouped together in tlie following table the humus 

 percentages of soil columns having similar texture and similar 

 characters in order to ascertain whether these have any influence 

 upon the amounts of humus. For the textural classification of 

 the soils we have used that of Professor Hilgard.^" the basis of 

 which is the percentage of clay in the soil. Thus soils with 

 3 per cent and less are cla.ssed as very sandy, those with from 

 3 to 10 per cent of clay as sandy, with from 10 to 15 per cent 

 as sandy loams, with from 15 to 25 per cent as clay loams, with 

 25 to 35 per cent of clay as clay soils, and those with more than 

 35 per cent of clay are classed as heavy clays, among which are 

 the adobes of California and other states of the arid west. 



Table 46. — Average of Humus in Lands op Different Texture at 



Various Depths 



Very sandy Sandy Sandy loam Clay loam Clay Heavy adobe 



1-3% clay 3-10% clay 10-15% clay 15-257c clay SS-SoVf clay -35% clay 



9 columns 15 columns 21 columns 23 columns 8 columns 10 columns 



Per cent Per cent Per cent Per cent Per cent Per cent 



1 ft 62 .81 .97 1.33 2.03 1.56 



2 ft 50 .62 .77 .98 1.25 1.23 



3 ft 37 .43 .55 .73 1.11 .95 



4 ft 31 .35 .43 .63 .89 .61 



oft 29 .35 .37 .48 .68 .43 



6 ft 21 .35 .31 .41 .52 .37 



7 ft 20 .31 .30 .34 .53 .28 



8 ft 14 .26 .24 .28 .40 .21 



Oft 12 .20 .19 .24 .37 .17 



10 ft 07 .19 .20 .22 .29 .17 



11 ft 04 .15 .14 .20 .19 .14 



12 ft 03 .16. .12 .19 .25 .13 



Sum of per cents: 



Upper 3 feet.... 1.49 1.86 2.29 3.04 4.39 3.74 



Upper 6 feet.... 2.30 2.91 3.40 4.56 6.48 5.15 



Lower 6 feet 60 1.27 1.19 1.47 2.03 1.10 



Entire column.. 2.90 4.18 4.59 6.03 8.51 6.25 



10 Soils (Macmillan & Co.), p. 84. 



