1919] 



Pendleton: A study of Soil Types 



425 



Altamont clan loam. — The percentages of nitrogen nitrified (tables 

 39 and 40, fig. 24) are as a whole lower than in the Diablo soils. A 

 similar relative effed of the several nitrogenous materials is seen, for 

 (NH 4 ) 2 S0 4 is first, cottonseed meal, second, the soil's own nitrogen 

 third, and dried blood fourth in the percentages of nitrates produced. 

 As in the Diablo soils the variation is not greal from soil to soil. 



San Joaquin sandy loam. — A wide range of variation (tables 11, 

 42, and fig. 25), from 1.2% to 4.5^ , is found in the Incubated control, 

 possibly due, in part, to the considerable variations in the physical 

 nature of the samples. The relative anion of the nitrogenous ma- 



\ s. N.+ -XII - 



\ S. \ • I ' ■ i. naeed Meal 

 A Soil Nitrogen 



\ S. N. + Dried Bl 1 



7 - lils 



Percentages of N. Nitrified 



Fig. 24. Graph showing the percentages of nitrogen in various nitrogen 

 containing materials nitrified in the three samples of the Altamont clay loam. 



t '-rials in the soils of the San Joaquin samples as compared with that 

 in the Diablo and Altamont soils is well shown by the following aver- 

 ages of the A horizon: dried blood had 0.02%. cottonseed meal had 

 0.33%, and ammonium sulfate had 0.56$ of the nitrogen nitrified, 

 while the incubated control had 2. 17' , nit rified. The soils are normally 

 low in nitrogen, and this, together with the poor physical condition, 

 made an unfavorable medium for any bacterial activity. This applies 

 especially to horizons B and C. 



Hanford fine sandy loam. — This is by far the most inexplicable 

 set of results in the nitrification studies (tables 13, 11. and fig. 

 The physical nature of this type is admirably suited Eor bacteriological 

 tumbler cultures, the soil being friable, not puddling readily, and 

 while in the incubator may be kept at the approximately optimum 

 • moisture content with Little difficulty. This property is fairly eon- 



