THE IERIGATION AGE. 



209 



SOIL DRAINAGE* 



By A. G. McCALL 

 Professor of Agronomy, Ohio State University. 



The soil is a mixture of very fine rock particles and 

 decayed organic matter from plants and animals. How- 

 ever, this material does not occupy all of the space. In 

 dry clay soil about one-half of the space is taken up by 

 the soil particles and the other half is occupied by air. 

 In sandy soils the individual air spaces are larger than 



Periwinkle Wilting on Account of the Lack of Film Water. 



in clay, but there are fewer of them and they take up 

 only about one-third of the entire space. 



For the best growth of crops about one-half of the 

 space not occupied by the soil particles should be divided 

 equally between air and water. If this space becomes 

 entirely filled with water, crops will not thrive, since their 

 roots will not be able to get the air necessary for plant 

 growth. Some plants, such as the cypress and the water 

 lily, have special structures which enable them to obtain 

 air from the water while their roots are entirely sub- 

 merged, but our common field plants do not have this 

 power. 



. The water that falls on our fields as rain would in 

 time completely saturate the soil if no drainage were pos- 

 sible. The more nearly level the land, the more readily 

 does the rain pass into it. During a long continued rain 

 the water soaks into the soil until, like a blotter or 

 sponge, it can hold no more. Then the excess of water 

 will flow over the surface to the lowest points in the 

 fields and finally join, the creeks and rivers which are 



The Same Plant 24 Hours After a Liberal Application of Water. 



a part of Nature's great drainage system. At the same 

 time, the water which has passed into the soil gradually 

 soaks into the subsoil and eventually finds its way to the 

 streams. If the soil is a loam or a sandy soil, this natural 



'Abstracted from "The Agricultural College," Ohio State Uni- 

 versity, December, 1911. 



drainage will be sufficient. In the case of most clay soils 

 Nature does her work too slowly to be of immediate 

 benefit. Then it is that we should supply artificial drain- 

 age to carry away the water more rapidly and thus assist 

 Nature. If the land is quite level, both open ditches and 

 tile drains may be necessary to accomplish the desired 

 results. 



Good drainage, then, is the first essential of a. pro- 

 ductive soil and the foundation upon which all permanent 

 soil improvement must be built. If good drainage is 

 lacking, the benefits which should come from manuring 

 and thorough tillage will not be realized to their full 

 extent. For their best growth, plants should have a moist 

 but not a wet soil; lack of moisture causes the leaves 



Corn Planted on a Poorly Drained Soil Will Have a Limited 



Root Development and Will be Unable to Withstand 



the Later Summer Drought. 



to curl and wither, and too much water in the soil causes 

 the plants to become spindling and yellow. 



Good drainage benefits the soil in many different 

 ways, the most important of which are the follojving: 



1. Drainage assists the soil in maintaining the 

 amount of moisture necessary for the best growth of 

 crops. After the excess of water has drained away, a 

 thin film of water remains around the soil particles. It 

 is this film moisture that is most useful to the plant, 

 because it supplies the growing rootlets with food dis- 

 solved from the soil, but does not prevent the free pas- 

 sage of air into the soil. 



After a long dry period this film may become so thin 

 that the plant roots will no longer be able to secure suf- 

 ficient moisture and the plant wilts, as shown in the 

 accompanying photograph of the periwinkle. 



2. Drainage by encouraging a deep root system, 

 enables the crops to withstand dry weather better. In 

 heavy, undrained soils the water passes downward so 



On Well Drained Soils the Corn Roots Strike Down Deep Into 



the Soil and Are Able to Secure Moisture from Below 



During the Dry Portion of the Season. 



slowly that the plants in their early srrowth send out only 

 a very shallow root system, because the standing water, 

 or water table, is so near the surface; our common plants 

 will not send their roots into free water to any great 



