LOSSES OF MOISTURE AND PLANT FOOD BY PERCOLATION 



BY G. S. FRAPS, PH. D., CHEMIST. 



Certain fundamental conditions are essential to plant life. These 

 include light, water, favorable temperature, favorable soil conditions, 

 and plant food. A deficiency of any one of these will limit the growth 

 of the plant. From the standpoint of plant nutrition, .no one is more 

 important than the others. From the viewpoint of the farmer, however, 

 the important conditions are those which, under ordinary agricultural 

 conditions, may be deficient and so control the growth of the plant and 

 the crop produced, and which, being deficient, may be supplied, to a 

 greater or less extent, or the deficiency controlled, by the farmer. In 

 other words, the practical farmer is not much concerned with condi- 

 tions beyond his control which limit plant growth, or those which are 

 favorable under ordinary agricultural practice. He is much concerned, 

 however, with deficiencies which he can correct or control. Tempera- 

 ture and light are little subject to control in agricultural practice, but 

 water, soil conditions, and plant foods ordinarily deficient phosphoric 

 acid, nitrogen and potash are more or less subject to control. The 

 quantity of rainfall cannot be regulated, but the amount of water stored 

 in the soil and that lost by evaporation may, more or less, be modified 

 by agricultural practices. 



QUANTITY OF WATER NEEDED. 



The quantity of water needed by the plant depends upon conditions, 

 but is very large. According to estimations of King, corn requires 233 

 to 272 pounds" of water to produce one pound dry matter. This does 

 not refer to the grain but to the entire plant. Barley requires from 262 

 to 774 pounds of water to produce one pound dry matter, and red clover 

 from 249 to 453 pounds. The quantity estimated by different investi- 

 gators varies, but we can assume, as a basis for calculation, that one 

 pound of dry matter requires 300 pounds of water. This quantity of 

 water is taken up by the roots of the plants and evaporated through 

 their leaves. An additional quantity of water is lost by evaporation 

 from the soil, during the period of growth of the plants. 



The amount of water required by plants* depends upon several con- 

 ditions : 



(a) Dryness of the air. Plants evaporate more water into a dry 

 atmosphere than into a moist. 



(b) The water in the soil. Plants evaporate more water from a 

 soil when wet than from the same soil when it contains a fair quantity 

 of moisture. 



(c) Light. More moisture is used in light than in darkness. 



(d) Fertility of the soil. Plants use less water when grown on a 

 fertile soil than when grown on a poor soil. The addition of needed 



*Fraps, Principles of Agricultural Chemistry, p. 120. 



