3 i4 SYSTEMS OF PERMANENT AGRICULTURE 



think, is the basis or reason in many cases for our crop rotation, viz., that these 

 excreted substances are not toxic alike for all plants, and the soil has time to 

 recover its tone and cleanse itself. I have told you that barley will follow po- 

 tatoes in the Rothamsted experiments after the potatoes have grown so long that 

 the soil will not produce potatoes. The barley grows unaffected by the excreta 

 of the potatoes, another crop follows the barley, and the soil is then in condition 

 to grow potatoes again." 



Again in the report of the Hearings before the Committee on 

 Agriculture of the United States House of Representatives, 

 under date of January 28, 1908, page 428, we find the following 

 statements by Professor Whitney: 



"The investigations of the Bureau of Soils, as to the cause of the deterioration 

 of soils, and the causes that limit crop production, have changed the viewpoint 

 of the entire world." 



On pages 445-449 of the same publication, Doctor Cameron 

 makes the following statements: 



" All soils contain practically all the common rock-forming minerals. Now, 

 it is a principle of chemistry that when a solvent is brought in contact with a 

 substance, that substance will go into solution until there is a state of equilib- 

 rium between the quantity of the substance outside and inside ; in other words, 

 we get sc saturated solution. If these rock-forming minerals were in all soils, we 

 should have the same solution in every soil, and that has been shown to be the 

 case. There are various variations, due to absorption, perhaps, of the soil. 

 In the first place, I must ask you gentlemen to remember that the soil and the 

 plant and the water in the soil is moving. The soil grains are constantly 

 moving, and the solution in the soil is constantly moving, and the growing 

 plant is constantly moving. If a plant stops for a moment, it dies. The soil 

 solution cannot stop for a moment, because it has to be moving all the time. 

 When water falls on the soil, part of it runs off the surface, and part of it runs 

 through the surface by gravitation and comes out in the subsoil, and part of 

 it starts and rises as soon as we get sunlight on the surface, and this part comes 

 up in films over and through the finer spaces, and is bringing with it dissolved 

 material from below. 



"The water that falls and goes through down and out goes rapidly through 

 larger openings, and gets very little of the soluble material, because it is not long 

 in contact with the soil grains. It gets some by reason of the fact that, as we 

 know, our springs and rivers and wells are all soil solutions, and carry mineral 

 matter. Now, water rising by capillarity cannot get very concentrated be- 

 cause it gets saturated with the minerals, and any excess that is contained in it 

 is thrown out, except in extreme conditions, as in the West, and then we get 

 alkali conditions; but under ordinary humid conditions we cannot have an 

 excess of it, and the soil solution is bringing materials from below which the 



