Effects of Subsoiling 139 



EXPLANATION OF THE MOISTURE EFFECTS OF 

 SUBSOILING 



The results stated show that subsoiling produces several very 

 distinct effects, so far as soil moisture is concerned, and these 

 may be stated as follows : 



1. Subsoiling increases the percentage capacity for water of 

 the soil stirred. 



2. Subsoiling decreases the capillary conducting power of the 

 soil stirred. 



3. Subsoiling increases the rate of percolation through the 

 soil stirred, or its gravitational conducting capacity. 



In order to understand how these effects are produced by sub- 

 soiling, it is necessary to have clearly in mind the nature of the 

 physical changes in the soil which the operation in question sets 

 up. In the small plot experiments which have been cited, the 

 subsoiling had the effect of increasing the pore space in the soil 

 stirred at the rate of over 245 cubic inches per cubic foot, or 14.2 

 per cent. Further than this, the pore space so added consisted in 

 a large measure of cavities which were so large that air and water 

 would move through them in obedience to the laws which govern 

 the flow of water through large pipes, rather than those control- 

 ling the flow through capillary tubes. 



It must here be born in mind that the increase of space was 

 made as large as it could well be, and hence that the results have 

 a maximum value. 



How subsoiling increases the water capacity of the soil stirred. 

 When a soil is broken into lumps which lie loosely together, and 

 these lumps are saturated with water, the many lumps behave 

 toward that water much as if each were a short column of soil 

 which is in contact with standing water. The surface film of 

 water which spans the pores at the surface of the saturated lump 

 of soil has a definite strength, and, if the lump is not too large, 

 can hold every cavity within that lump completely full of water, 

 just as the lump of sugar dipped into the tea and then withdrawn 

 comes forth completely filled with the fluid. But when the soil 



