372 BOARD OF AGRICULTURE. [Pub. Doc. 



HINTS ON LAND DKAINAGE. 



BY WM, "WHEELER, ENGINEER TO THE BOARD. 



All plants with wkioh agriculturists and horticulturists 

 concern themselves are air plants, in that their roots are 

 dependent upon air in the soils in which they grow. Con- 

 sequently the available depth of any soil for agricultural 

 purposes is practically limited to the depth to which air 

 can penetrate it, and cannot exceed, therefore, that part of 

 it which is above the water table, or the level at which water 

 of saturation stands in the ground. 



- Effects of Land Drainage. 



It is the primary object of artificial drainage, then, to 

 increase the effective depth of soils and to improve their 

 general character by lowering the water table in or under 

 them. Among its benefits and advantages are the follow- 

 ing : — 



First. — It increases (with the aid of the deeper cultiva- 

 tion permitted thereby) the amount of soil space and material 

 for the root-feeding of plants and for bacterial action and 

 other agencies in vegetable nutrition.* 



Seeond. — A greater proportion of the rain and snow 

 water leaches through and surrenders to a well-drained soil 



* The degree of moisture has a marked influence upon the activity of the micro- 

 organisms of the soil which aid in the nutrition of plants, especially the root-tubercle 

 bacteria and bacteroids, through which leguminous plants, such as lupines, beans, 

 clovers, alfalfa, etc., assimilate or fix free nitrogen from the air. 



Experiments by E. Gain indicate that the development of such tubercles is about 

 twenty times greater in moist soil than in dry soil, with a corresponding increase in 

 the assimilation of free nitrogen. They also lead to the conclusion that a medium 

 amount of moisture in the soil (flfty per cent of that required for complete satura- 

 tion) is more favorable to the development of root tubercles than higher or lower 

 amounts. (United States Experiment Station llecord: Vol. V., pages 110-113; 

 Vol. VI., page 870.) 



