410 University of California Publications in Agricultural Sciences [Vol. 3 



Magnesium as MgO 



Diablo clay adobe. — This type shows a moderate variability in the 

 magnesium content, with from 1.13% MgO to 3.26%, averaging 

 2.09%. The largest quantity is three times that of the smallest 

 (tables 24, 25, figs. 15-18). 



Altai)) out clay loan). — Within the three samples of this type the 

 range in the MgO content is very great, from 0.077c to 1.90%, with 

 the average of 1.05%. The largest is twenty-seven times that of the 

 smallest. 



San Joaquin sandy loam. — The total MgO in the samples of the 

 type is low, considering that some soils reported by Hilgard contain 

 from 1% to 3% magnesia by the acid digestion. The variation within 

 the A horizon is from 0.34% to 0.90%, with the average of 0.62%, i.e.. 

 the largest is three times the smallest. The quantities in the B horizon 

 are somewhat erratic as compared with those of the surface, yet in 

 both the B and C horizons the results approach those of the surface 

 sufficiently to give a rough parallelism. The greater amount of clay 

 and fine silts with the increase of depth gives, as one would expect, 

 an increase of magnesium. The average MgO content in the B horizon 

 is 0.81%, and in the C horizon 1.05%. 



Table 24 — Magnesium as MgO 

 (Surface horizon only) 



