EXPERIMENTS WITH 15N AT THE ROLE OF THE E XTRACTABLE ORGANIC SOIL-N IN THE PROCESS OF THE NITROGEN-SUPPLY

The immobilization of 15N-fertilizer doses for cereals and faba beans and the incorporation of the 15N into the hot-water soluble organic so il-N-fraction were tested in combined field-, pot- and lysimetertrials . About one tenth of the immobilized 15N was accounted into the hot-wa ter extract. This amount was nearly the same as the 15 N uptaken by th e following cultures. But it was uncertain, if this extractable nitrog en was realy the source of the N-mineralization. After faba beans an i ncrease of the total organic N-content in the soil was analyzed and al so a surplus yield of the following cereals - but a corresponding incr ease of the extractable nitrogen was not detectable.