I] 



THE NATURE OF HUMUS 



51 



nd roughly classed as humus. The splitting-up process 

 ontinues in the soil, so that humus becomes one of the 

 reat sources of nitrogen for the food of plants, and a 

 oil well supplied with humus is generally regarded as 

 srtile. 



During the formation and continued decomposition 

 f humus the carbohydrates appear to be first attacked, 

 nd the nitrogen-containing bodies, e.g., the nucleins in 

 articular, resist the action of bacteria. For this reason, 

 mere we find the proportion of humus in a soil is low, 

 he proportion of nitrogen in the humus itself will be 

 igh, the decay of the humus falls more heavily on the 

 >urely carbonaceous part of the material. 



This is seen in the figures obtained by Lawes and 

 rilbert for the ratio that exists between the propor- 

 ions of carbon and nitrogen in various soils : 



Hilgard and Jaffa also found that the humus of soils 

 1 an arid climate, where the deficiency of rainfall causes 

 iq soil to be very open, contains a higher proportion of 

 itrogen than is found in the humus of damper soils : 



