SOIL SESSION. lOl 



the soil had furnished ; but when the farmer begins his operations he 

 not only stimulates a greater draft upon the soil by cultural methods 

 which cause a larger growth than would otherwise have taken place, 

 but, instead of permitting this growth to return to the land, he re- 

 moves the major portion of it, leaving only the roots and a little 

 stubble. Further than this the cultivation, which enables his crop to 

 secure a larger supply of plant food from the soil, also sets up condi- 

 tions which involve a considerable waste of that supply, unless these 

 conditions are understood and the waste prevented by intelligent man- 

 agement. For example, in the Rothamsted experiments, more than 50 

 years ago, an acre of land was set aside for a study of the effect of 

 fallowing; half thrs acre being sown in wheat each year and the other 

 half being fallowed, th.e two halves alternating each year. The result 

 has been that the average produce from this acre for 40 years was 8 5- PI" 

 bushels, while that from land adjoining, growing wheat every year, was 

 12 3-4 bushels per acre, thus showing that a bare fallow may consume 

 half as much fertility as a crop of grain. 



The explanation of this outcome probably lies in the fact that the 

 processes which we call decay, and through which the roots and other 

 remains of vegetation left in the soil are decomposed and made avail- 

 able for future plant growth, are also vegetative processes, due to 

 the work of micro-organisms, similar in function to those which have 

 already been mentioned. 



'J'hese are the so-called nitrifying bacteria. They are constantly 

 at work in the soil when the temperature is above the freezing point, 

 and their work is greatly facilitated by tillage and cultivation. Their 

 function is to tear down and decompose the vegetable debris in the soil, 

 to convert its inert nitrogen into nitric acid, and at the same time to 

 liberate its mineral constituents. If there be a growing crop on the 

 land its roots will absorb the plant food thus set free; but if there be 

 no such crop this available plant food, both nitrogenous and mineral, 

 will be largely carried into the drainage waters, in humid climates and 

 lost, or in case the rainfall does not exceed evaporation, the unused plant 

 food will accumulate in the soil, the nitric acid combining with lime or 

 other alkaline base to form a nitrate salt, thus explaining the great 

 fertility of the soils of the arid regions and the increased crops which 

 have been observed to follow seasons of drouth in humid countries. 



If the soil be deficient in lime, however, or other alkaline base, the 

 accumulation of nitric acid may possibly cause, or assist in causing, the 

 injurious acidity which is being observed in some of our badly worn 

 soils. 



