Relation of Soils to Moisture and Air 45 



rapidly carried downward by the rain water out of the 

 reach of plant roots. In such a soil constant applications 

 of manure and fertiUzers are essential to the production of 

 crops and the accumulation in it of organic decay that 

 will tend to make it more retentive of moisture. Then, 

 too, the depth to which the water percolates and the feeble 

 capillarity of a coarse sand makes the rise of water in such 

 soils less than where there is a retentive subsoil near at 

 hand. These sandy soils, however, yield up to plants 

 their water more completely than a clay loam. Professor 

 King reports that he foimd corn able in a sandy soil to 

 draw down the water content of the soil to 4.17 per cent., 

 while in a clay soil with a much greater water capacity 

 the corn crop could draw it down only to 11.79 per cent. 

 In all soils there is a point below the sur- 

 ^f^w ^ ^®P*^ face where water is constantly present. This 

 table i^ called the water-table. Where this is too 



near the surface the soil is rendered cold, 

 and the chief value in tile underdrainage is in lowering this 

 water-table so that the air can penetrate deeper in the soil 

 and there will be a greater depth of soil containing only 

 the capillary moisture that is needed by the roots of plants. 

 Much of the greater productivity of the lowlands or bot- 

 tom lands is due to the fact that the permanent water-table 

 in the soil is nearer to the surface than on the uplands, and 

 hence the capillarity of the soil can bring moisture to the 

 roots more readily and constantly. 



The water-table in good arable soils should always be 

 four feet or more below the surface, and as a matter of 

 fact it is on the uplands generally from ten to fifty feet 

 down. What concerns us mainly in agricultural opera- 



