OCR Text |
Show POISONOUS SUBSTANCES FORMED IN THE SOIL I . BY PLANTS. i By J. C. Hogenson. t The Bureau of Soils of tho U. S. ,j Department of Agriculture has re- j ccntly added a new factor to the i causes of soil fertility. The claims 1 of the Bureau arc that practically all I soils contain a sufficient supply of 1 mineral plant food for crops to grow I indefinitely, and that plants give off or excrete from their roots certain toxic substances into the soil. These I by accumulating thosr Dccomc poi- 4" sonous to the plants that produce them. On the same principle as a .man being shut up in a tightly closed room will soon cause the air in that f I room to become poisonous to him by exhaling poisonous gases into it. sonous to him. Every kind of iplant , excretes a substance that is poison-JU poison-JU ous to itself, but this substance may jl not be detrimental to other crops and may even be beneficial. By growing the same crop, say wheat, upon the ! same land year after year, the toxic or 1 poisonous substance given off by the roots of the wheat plants accumulate to such an extent that the soil actually ac-tually becomes poisonous to wheat plants and they refuse to grow there. If now other crops be grown on that land or it be followed, these toxic substances disappear and wheat can again be grown there. Thus -we have the benefits of rotation. If manures or fertilizers be added to this soil, they have the power of neutralizing the poisonous- sub stances so that wheat can again be grown there. The manures or fertilizers fer-tilizers also add new .plant food to the soil but .this is .1 secondary consideration, con-sideration, as the principal reason for adding it is to neutralize the toxic substances excreted iby the roots of the previous crop. This in short is the theory, of which we have recently heard so much, advocated ad-vocated by the Bureau of Soils. |