200 Physics of the Soil 



water is then free to move rapidly downward through the 

 large non-capillary pores, urged by the strong force of 

 gravity. Not only this, but, since the pores are many of 

 them too large to be filled by the percolating streams, there 

 is left an easy egress for the soil-air, which must escape 

 upward before the water can enter, and this does not re- 

 tard percolation as it does in a compact soil. 



233. A Larger Percentage of the Moisture of Subsoiled 

 Ground Available to Crops. When a soil has been made 

 more open by subsoiling, and its capacity for holding water 

 thereby increased, this extra amount of water retained be- 

 comes wholly available to crops. It was shown in (161) 

 and (162) that there is a certain per cent, of water in a 

 soil which the roots of plants are unable to remove with 

 sufficient rapidity to meet their needs and as this amount 

 depends upon the size of the soil grains, which subsoiling 

 does not alter, the increased percentage held becomes a 

 clear gain to the crop. 



234. Dangers From Subsoiling. One of the most serious 

 difficulties associated with subsoiling, aside from the ex- 

 pense, is the danger of puddling, and this is particularly 

 great in humid climates where the subsoil, especially in 

 the spring, is liable to be too wet. The danger is intensi- 

 fied on account of the fact that the surface soil may be 

 in good condition for plowing when that below is much too 

 wet. If this work is attempted when the ground is not in 

 condition very great harm may be done and so it is gen- 

 erally much safer to subsoil late in the fall in humid cli- 

 mates, when the* deeper ground is generally dryest. 



235. Early Seeding. When the crop is started to grow- 

 ing upon the ground as early as the temperature of the 

 soil and of the air will permit the farmer is conserving v soil 

 moisture, by taking advantage of that which otherwise 

 would be lost by surface evaporation, and enabling his crop 

 to use this in growth. Such timely planting may not only 



