86 SOILS 



The water in the soil, both free and film, is not pure 

 but has in it various salts and elements that it has 

 dissolved from the soil. Some of these are plant 

 foods. The nitrates, containing that most ex- 

 pensive of plant foods, nitrogen, are most likely to 

 be carried off in this way; also the phosphates and 

 the potash salts to some extent. Most any kind 

 of farm plant will grow very well in the water 

 caught from a drain tile, and nothing else, showing 

 that this water contains as much plant food as 

 that which the plants in the soil draw up through 

 their roots. 



The coarser a soil is, and the less humus it con- 

 tains, the less able is it to retain the rain that falls 

 upon it. It takes longer for water to seep down 

 through clay soils, in which the spaces between 

 the particles are very small, than through a sandy 

 soil, in which the spaces between the grains are 

 much larger. This is why sandy soils are leachy. 

 The loss of water from clayey soils, through seep- 

 age, is much facilitated by the burrows of eartn- 

 worms and the decay of roots, both of which open 

 channels; also, to a considerable extent, by the 

 numerous cracks that appear in all clay soils as 

 they dry. These cracks are often very large on 

 the surface; smaller though less numerous cracks 

 are found for several feet below. 



With the exception of very sandy soils, the loss 

 of water by seepage is not likely to occur during the 

 growing season. In most parts of the country the 

 upper soil becomes so dry during the summer that 

 tne summer rainfall is mostly taken up or evapo- 

 rated before it is lost by seepage. It is during the 

 season when vegetation is dormant or inactive, 

 which is usually when the precipitation is largest, 

 that the loss of water by seepage, and the loss of 



