EFFECT OF FERTILIZATION ON ORGANIC AND MICROBIAL BIOMASS NITROGEN USING N-15 UNDER CORN (ZEA-MAYS L) IN 2 QUEBEC SOILS

Changes in soil organic N following fertilizer N applications are rela ted to soil quality and subsequent N uptake by plants. Recovery of fer tilizer N as organic N and soil microbial biomass N within two corn (Z ea mays L.) fertilization systems was studied using N-15 On a Chicot s oil (fine-loamy, mixed, frigid, Typic Hapludalf) and a Ste. Rosalie so il (fine, mixed, frigid, Typic Humanquept) in southwestern Quebec in 1 989 and 1990. The two fertilization systems studied received a recomme nded rate of 170-44-131 kg (normal rate) and a high rate of 400-132-33 2 kg of N-P-K per hectare. Increasing fertilization rates above normal increased microbial biomass N immobilization with a subsequent greate r N release. Higher fertilization rates significantly increased both t he magnitude of soil microbial biomass N and microbial fertilizer N re covery in the soil microbial biomass.