Drainage in New York. 253 



capacity is increased. The soil is then able to both readily absorb the rain- 

 fall and to retain a larger proportion of it than would otherwise be pos- 

 sible, against the time of dry weather. Second, the wider and deeper dis- 

 tribution of the plant roots in drained than in wet soil puts them in reach 

 of a much larger reservoir of moisture. This effect is well known to those 

 who have had experience in tile drainage. Mr. Johnston was aware of the 

 effect since it is reported that his Dutch neighbors laughed at him for 

 "burying crockery," saying his crop would be "all dried up before it was 

 half grown," but they remained to be amazed at the great superiority of 

 Mr. Johnston's crops over their own at harvest time. Drainage is a de- 

 sirable practice for dry weather as well as for wet weather. 



(4) Drainage promotes the aeration of the soil, that is, the exchange 

 between the soil air and the external air. A supply of oxygen is necessary 

 to the proper growth of the living organisms in the soil. Such a supply 

 is largely, if not entirely, excluded from a saturated soil. The removal 

 of the water makes a place for air and the granulation or loosening-up 

 process which occurs facilitates the movement of the air into and out 

 of the soil. The supply of air increases the food available by its direct 

 action on the minerals in the soil and by promoting the growth of desirable 

 bacteria. It also hinders or prevents the growth of many undesirable 

 bacteria. 



(5) Drainage permits the soil to maintain a higher average temperature 

 than is possible on wet soil. This effect is well known and is generally 

 recognized. Not only has the increased temperature been observed in 

 practice, but it has been demonstrated experimentally to be a very con- 

 siderable amount. A clay soil holds more moisture than sandy soil and 

 from this fact has arisen the descriptive term " cold soil " applied to clay 

 and " warm soil " applied to sand. The dry soil in each case requires 

 nearly the same amount of heat to warm equal masses, the difference in 

 temperature resulting from the difference in amount of moisture retained 

 under field conditions. How great is this difference in temperature which 

 may result from poor drainage is shown by the following calculation based 

 upon well known facts. 



The evaporation of one pound of water from a cubic foot of compact 

 clay, which is saturated with water, absorbs enough heat to lower the tem- 

 perature of the cubic foot of wet soil 21° F. The evaporation of the same 

 amount of water from a cubic foot of saturated sand soil would be suffi- 

 cient to lower its temperature 25° F. If, on the other hand, the heat 

 necessary to evaporate one pound of water is used to raise the temperature 

 of the soil containing only the optimum amount of capillary moisture the 

 temperature of the cubic foot of clay would be raised 29° F. and that of 

 the sand 32° F. And if all of the excess of water in a cubic foot of 

 either material were removed by evaporation, enough heat would l^e used 

 to raise the well moist clay through 380° F. and the sand through 300° F. 



