216 THE WASTE AND CONSERVATION OF PLANT FOOD. 



soon be leached out of a soil. On the other hand, lime, even when sup- 

 plied as hydrate, in which case it is somewhat soluble, quickly becomes 

 converted into a carbonate which is practically insoluble in water which 

 does not contain an excess of carbon dioxide. 



I am aware of the fact that liming to prevent erosion by surface 

 drainage has not been emphasized as an example of the benefit of the 

 proper chemical treatment of soils, yet I feel sure that all who will give 

 the subject a thoughtful consideration will agree with me in saying that 

 this aspect of the subject is one of no small importance, especially 

 when considered iji respect of hilly fields, and even of fields of more 

 level surface. 



Without dwelling long upon this point, it is oidy necessary to call 

 your attention to the immense quantities of soil material annually con- 

 veyed to the sea by the causes of erosion already mentioned to show 

 ^^ hat an active and powerful foe the farmer has in this source of loss. 

 Anyone who watches, even for a short time, the volume of water carried 

 by the Mississippi into the Gulf of Mexico will have a most effective 

 object lesson in regard to this source of loss. 



A more striking lesson may be seen iu the hill regions bordering 

 both banks of the Ohio River. Hundreds of fields once covered with 

 sturdy forests of oak, maple, and walnut, and afterward bearing large 

 crops of maize, tobacco, and wheat, may now be seen furrowed with 

 gullies, as with the wrinkles of age, and abandoned to brush and briers. 

 The same is doubtless true of other liill regions, but I speak the more 

 advisedly of those which have come under my personal observation. 



Great, however, as the mechanical loss of plant food is, it is by no 

 means as dangerous as the loss of the soluble materials caused b}^ the 

 percolation of the water through the soil. The study of the nature of 

 the loss of these soluble materials, together with the estimation of 

 their amount, forms the subject of lysimetry. Agricultuial chemists 

 have used many devices for the purpose of determining the character 

 and amount of the natural drainage of soils. Evidently the treatment 

 of a specially prepared x>ortion of soil by any solvent, although giving 

 interesting results, does not indicate the natural course of solution. 

 The only way in which this can be determined is to be al)le to collect, 

 measure, and study the char-acter of the draiuage from a given portion 

 of the arable surface of the earth in situ and under normal conditions. 

 Various methods of lysimetric investigation have been proposed and 

 used, all of them possessing many points of value. 



An excellent system of such observation has been established, fin- 

 instance, at the Agricultural Experiment Station of Indiana. It is not 

 my purpose, however, to discuss the mechanical details of lysimetry, 

 but only to call your attention to the main principles which underlie it. 

 The movement of water near the earth's surface is a matter of especial 

 interest to agriculturists. Whitney ^ has clearly pointed out that the 



'"Some physical properties of soils," United States Weather Bureau, Bulletin 

 No. 4. 



