44 The Ottawa Naturalist. [June 



to-night, is dependent in a very large degree for its value upon 

 the fact that it adds vast quantities of this material to the soil. I 

 shall endeavour to do this very briefly. 



The Agricultural Importance of Humus. 



ist. It is the natural store-house and conservator of nitrogen, 

 which element is the most expensive of all plant foods when it 

 becomes necessary to purchase it in commercial fertilizers. 



2nd. It furnishes the food upon which the soil micro- 

 organisms live and which by their life functions convert its organic 

 nitrogen into nitrates. 



3rd. It possesses considerable amounts of the mineral food 

 constituents. These, in the further decomposition of the humus — 

 a process continually going on in summer — are liberated in forms 

 available to growing crops. We have reason to believe from 

 recent research that the mineral humates furnish a large propor- 

 tion of the potash, lime, etc., used by crops. 



4th. It serves to increase the absorptive and retentive power 

 of soils for moisture. 



5th. It regulates and protects against extremes of soil tem- 

 perature. 



6th. It opens up and mellows heavy soils. 



7th. It serves to materially diminish the loss of fertilizing 

 elements by drainage, thus permanently improving in the best 

 way light soils. 



From these considerations, it is evident that humus is to be 

 regarded as a soil component of a very high order. 



The relation of humus content to nitrogen present in soils of 

 similar origin under similar meteorological conditions, is practic- 

 ally constant. It has been noticed that the amount of humus pre- 

 sent gives an excellent though not an infallible indication of the 

 amount of organic nitrogen the soil possesses. Further, it has 

 been observed that as the humus disappears the nitrogen goes with 

 it. Cultivation, that is, exposing the substance of the soil to the aic, 

 as by our ordinary farm methods with the plow, harrow, etc., 

 tends to dissipate the humus and, as a natural consequence, to 

 decrease the nitrogen. Soils growing grain exclusively year after 



