SOYBEAN NITROGEN CONTRIBUTION TO CORN AND RESIDUAL NITRATE UNDER CONVENTIONAL TILLAGE AND NO-TILL

Soybean (Glycine max L. Merill) can produce high-N residues that may b enefit subsequent corn (Zea mays L.) production, but the degree of ben efit is often unpredictable and may be related to tillage methods. Thi s study investigated the effects of conventional-tillage (CT) and no-t illage (NT) on fertilizer replacement values for corn in a corn-soybea n rotation. Field experiments were conducted for two growing seasons o n two soils, a Ste. Rosalie clay (Humic Gleysol), and an Ormstown silt y clay (Humic Gleysol). Continuous corn, corn following soybean, soybe an following corn, continuous soybean, and three levels of fertilizer N (0, 90, 180 and 0, 20, and 40 kg N ha(-1) for corn and soybean, resp ectively) were compared. Tillage did not effect yield or N uptake cons istently. Corn grain yields and N uptake were greater following soybea n than following corn. Soybean provided N fertilizer credits ranging f rom 40 to 150 kg N ha(-1), which was greater than the residual NO3 in the soil prior to planting. Credits were greater in the year with high er corn yields and lower previous winter precipitation resulting in gr eater NO3 carryover. Tillage effects on N credits from soybean differe d between the sites. Consequently, N contributions of soybean to corn could not be related to tillage method or soil type.