SOILS 97 



the power of the soil to hold and move moisture. The size 

 and arrangement of the soil particles are of great importance 

 in farming operations. Clay holds so much moisture because 

 of its fine texture, and gives it up so slowly that farmers 

 call such soils cold and heavy. A good soil should be a bal- 

 anced mixture of these soil materials. 



Soil water. We cannot think of soil without noting its 

 close connection to the water it contains, or should contain. 

 The function of water in the soil is to supply plant-food, 

 to dissolve mineral, plant-food elements, and to carry them 

 in solution by capillary attraction to the roots of the plants. 

 There are three forms of water in the soil : first, the free or 

 gravitational water ; second, the capillary water ; third, hygro- 

 scopic water. The gravitational water is the excessive water 

 which we seek to remove by drainage. It seeks its level at 

 the water table of the ground. The capillary water is the 

 water adhering to soil particles and drawn by capillary attrac- 

 tion to the drier areas. It is the most important form of 

 water for the use of the plant. Hygroscopic water is the 

 water in the form -of a very thin film about each particle of 

 soil. This water can not be removed except at very high 

 temperature, and it has little value, perhaps, in plant growth. 



The presence of water in the soil is one of the controlling 

 factors in crop production. The farmer may have some 

 control over the water supply of the soil: he may increase 

 the water content by incorporating in his soil more organic 

 matter, thus decreasing loss by percolation; he may provide 

 the soil mulch, preventing evaporation of the water from the 

 soil; he may deepen the soil by cultivation, thus increasing 



