562 IOWA DEPARTMENT OF AGRICULTURE 



Water, which affects the soil, exists in two conditions: 



First. Hydrostatic water, which is visible to the eye and free to obey 

 the laws of gravity, and it will pass off through drains either artificial 

 or natural. 



Second. Capillary water. This is water held within the fine pores of 

 the soil by the surface attraction of its particles, and is commonly called 

 moisture, and is water left in the soil after it is drained. 



In general terms, about 50 per cent of the volume of a soil is empty 

 space; that is, it contains only air and water. The results of experiment 

 show that the volume of empty space varies from 37 per cent in sandy 

 soils to 65 per cent in soils composed largely of clay. 



How drainage operates — that is, how it effects the soil. It would be 

 no difficult matter to collect a volume of experiments which were to ascer- 

 tain the precise working of drainage. 



One of the cheapest, simplest and at the same time most satisfactory 

 experiments to determine the advantage of drainage is as follows: 



Take two ordinary earthenware flower pots, the one having a hole 

 in the bottom and the other to be without any holes in either bottom 

 or sides. Fill both with precisely the same quantity and quality of soil, 

 and plant in each either growing plants or seeds of any ordinary cultivated 

 product. One will represent a drained soil, while the other represents an 

 undrained one. Give both the same exposure and the same quantity of 

 water. 



If seeds are sown in both, those in the perforated pot will germinate 

 the soonest and the plants become the thriftiest and hardiest. Sometimes, 

 though seldom, the seeds in the advanced pot will not germinate at all, 

 although they produce only sickly and slender plants. In this manner 

 the effects of drainage can be completely demonstrated. If both flower 

 pots are placed in earthen saucers and the water poured into the saucers, 

 that pot having the holes in the bottom will absorb the water by capil- 

 lary attraction and the plant will receive its due proportion and thrive, 

 while the unperforated pot will not absorb any water and the plant will 

 suffer from drought — thus showing the benefit of drainage in times of 

 drought. A belief has obtained that drains are of advantage to the soil 

 only when they are conducting away surplus water from showers. 



It certainly is a great advantage to plants to be relieved from sur- 

 plus water as soon as possible, but it is at the time no less an advantage 

 to be supplied with new oxygen, and to have the old removed. An under- 

 drained soil cannot make these changes in its gases, for the benefit of the 

 plant, as well as a drained soil. This aeration of the soil is absolutely 

 necessary for the health and growth of the plant. Plowing is nothing 

 more or less than aerating the soil, and everyone familiar with farming 

 operations is well aware that plants grow best on a finely pulverized 

 soil. That is, in other words, on a well aerated soil. 



Oxygen is no less essential to the roots of plants than it is to the 

 lungs of animals, but if the oxygen is not changed, the result is very 

 unfavorable to the plants. Every rain that falls on a porous or well 

 drained soil brings new solvents of the inorganic materials which nour- 



