12 



SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. 



NITRIFYING POWER OF SOILS AT DIFFERENT DEPTHS. 



In investigations in soil bacteriology in the eastern United States 

 only the surface soil shows great variations. The soil of the arid 

 sections is much deeper, however; that is, the subsoil is less ''raw" 

 than in regions of heavier rainfall, a fact that has come to be more 

 or less familiar to everyone studying soil conditions over extensive 

 areas. 



Figure 2 shows the nitrification of samples from plats 100 and 110. 

 These plats, which are practically duplicates, are in a productive 



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80 



70 



60 



50 



40 



30 



20 



10 







-10 



DEPTH /IT WH/CH S/IMPLES l^ERE T^^/fif/V. 

 tOW__6"7tJl2" l2"rol8" (8'ro24" 24ro36" 



5ulphofi S:fM_/J0_^ z^^ 



,^ • — -^ CMor/ds -P/a f //o ' ~~—~ - 





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600 



700 



600 



500 



400 



300 



200 



100 







-100 



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Fig. 2.— Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths 

 from plats 100 and 110, Truekee-Carson Experiment Farm. Original nitrate present in samples from 

 plat 100: Depth, to ti inches, 8 parts per million; (i to 12 inches, 15; 12 to 18 inches, 9; 18 to 24 inches, 4.8; 

 24 to 36 inches, 6.50. From plat 110: Depth, to 6 inches, 9 parts per million; 6 to 12 inches, 7.4; 12 to 

 18 inches, 5.2; 18 to 24 inches, 4.8; 24 to 36 inches, 3.12. 



alfalfa field which has been under cultivation for several years. The 

 soil is loose and sandy throughout the 3-foot depth. The nitrate 

 curves show that there is a gradual decrease in nitrifying power with 

 depth. 



Figures 3 and 4 show the nitrification in samples from ])lats 120 and 

 130. These are in a fertile alfalfa field similar to the one mentioned 

 '111 



