IV.] CULTIVATION AND SOIL WATER 103 



the ground and establishes a continuous liquid film 

 from the subsoil water right up to the surface, it should 

 be renewed by a fresh cultivation as soon as the land 

 will admit of working. It is often noticed that a casual 

 shower during a dry period, or watering a garden unless 

 the operation is done very thoroughly, may result in a 

 greater drying up of the soil than ever, just because 

 a film of water is created able to lift water from the 

 subsoil up to the evaporating surface. The loose hoed 

 ground practically forms a mulch, though the protect- 

 ing material is the soil itself instead of straw or kindred 

 substances. 



Of course, the conservation of soil moisture is 

 not the only good effect brought about by the surface 

 cultivation during the summer: the aeration of the 

 soil, the mechanical distribution of the nitrifying 

 bacteria that is effected, the warmth of the surface 

 layers due to their dryness, all combine to render 

 nitrification active, and to bring into a form available 

 for the plant the reserves of nitrogen in the humus of 

 the soil. This point will be dealt with more at length 

 later : for the time, it will be sufficient to remind the 

 reader how a turnip crop with its frequent spring and 

 summer cultivations is almost independent of any 

 nitrogenous manure, though it removes something like 

 100 lbs. of nitrogen per acre : whereas a wheat crop, 

 removing less than half that quantity of nitrogen per 

 acre, often requires the application of a nitrogenous 

 manure, because it is grown on undisturbed soil in 

 the cooler season of the year. 



The saving of soil moisture which can be effected by 

 hoeing is illustrated by one of King's experiments, 

 when, during a dry period, the soil on a piece of land 

 kept cultivated to a depth of 3 inches was sampled from 

 time to time down to a depth of 6 feet, samples being 



