Fertility Influenced by Drainage 13 



to a lower level, where they may be taken up by the 

 deeper -feeding roots. Here, then, we are led to see 

 one of the ways in which water, applied at the sur- 

 face at opportune times, acts as a wonderful stimulus 

 to plant growth. 



If, now, we turn from the irrigation to the draiti- 

 age side of the same problem, we shall see in another 

 way how fundamentally important this principle is. 

 Let a soil be inadequately drained, and the roots of 

 the plants will be forced to occupy the surface soil, 

 for they cannot abide in the water -logged region. 

 Then, if heavy rains come and percolation results, all 

 of the unused nitrates which may have been in the 

 soil at the time are at once washed below the roots, 

 and perhaps entirely lost to the crop. But, on the 

 other hand, if the soil had been properly drained, so 

 that the roots of the crop could have been two, three 

 or four feet below the surface, then, as has been pointed 

 out, the nitrates would have been washed to the roots, 

 where they would have become at once available'. 

 Then, too, when a dry period comes, with all the life 

 processes going on in the soil confined close to the 

 surface, the great demand for water from the roots 

 forces them at once to so completely dry out the sec- 

 tion they occupy that a violent check is at once put 

 both upon the plant itself and upon all the food-form- 

 ing processes in the soil ; for, under these conditions, 

 it is usually impossible for capillarity to keep pace 

 with the loss of water from above, and the soil quickly 

 becomes too dry. 



So far we have been speaking of the importance of 



