44 DRY FARMING 



Humus, the accumulated residue of the decomposl 

 tion of plant remains, plays an important role in the 

 physical properties of soils. Being somewhat plasti( 

 and spongy in nature, it binds the sand particles to- 

 gether, giving such soils greater adhesiveness and henct 

 better tilth. In clay it binds the small particles to- 

 gether into larger aggregates, thereby lessening the 

 plasticity and rendering them easier to work. Due tc 

 its porous nature it increases the water-holding 

 capacity, facilitating the, absorption and retention of 

 water. It increases the pore-space, alloAving the air to 

 circulate more freely in the heavier types of soil, there- 

 by increasing the warmth, and making the soil ''^earlier". 

 The importance of keeping up the humus content from 

 the standpoint of the physical properties of the soil is, 

 therefore, important; the role from the chemical and 

 biological standpoints will be discussed later. 



The capillary rise of water in soils is controlled by the 

 size and compactness of the soil particles. Although 

 water rises more rapidly in a sandy soil because of less 

 resistance, the total height to which it will rise and the 

 force exerted in the upward rise are greater in the 

 heavier types. Soil-packing, therefore, results in bet- 

 ter capillary contact besides assisting in the decay of 

 vegetable matter by the closer contact with moisture. 



32. Dry-Farming and Soil Physics. — Dry-farming puts 

 into practice our knowledge concerning the physical 

 properties of soil. For example we plow for summer- 

 fallow before the last of the heavy summer rains come 

 in order to render the soil more open and retentive of 

 moisture. The use of the soil packer on fall and spring 

 plowing is to lessen the air space in the soil and to 

 aid in bringing the moisture up to where the seed is to 



