1919] Pendleton: A Study of Soil Types 403 



the "black pigment." Soil no. 26, probably the only virgin soil in 

 the series, shows a particularly hjgh content of humus for such a soil, 

 though from the color of the soil one would suspect but very Little 

 humus. The agreement between the three horizons of the San Joaquin 



sandy loam samples is close. The average content of humus was 

 0.68$ in the A, 0.51% in the B, and 0.38* , in the C horizon. 



Han ford fine sandy loam. — The variations in humus content in this 

 type are greater than in any of the others (table 19, and fig. 18). This 

 is possibly because of two factors: the open texture of the soil, hence 

 the rapid loss of organic matter by oxidation processes; and secondly, 

 the high agricultural value of this soil, which has led to a greater appli- 

 cation of fertilizers than has been the case with the other soils. The 

 actual variations in the humus content are large, 0.7', to 2.1% with 

 the average of 1.15% for horizon A, from 0.5% to 1.8',' with the aver- 

 age of 0.81% for B, and from 0.44"; to 1.07$ with the average of 

 0.59% for C. The extra-typical sample no. 14 is above any of the 

 others in the total humus content. The variations in the subsoil 

 humus content are more or less parallel to those of the surface soil. 



The following averages of the humus content of horizon A, Diablo 

 1.26'/ , Altamont 1.24%, San Joaquin 0.68/ , Hanford 1.15%, show 

 that there is not much difference between the soils, except for the San 

 Joaquin sandy loam, which has an average of half the others. Within 

 the type the soils may be nearly alike, as in the San Joaquin and Alta- 

 mont, or may be variable to a large degree, as in the Hanford. The 

 variations in the humus content of the soils are small, considering the 

 diverse nature of the soils, and the usual methods for judging the 

 quantity of humus. 



Table 16 — Humus (and Humus Ash) 

 Diablo Clay Adobe 



