Abstract
Soybean (Glycine max L. Merill) can produce high-N residues that may benefit subsequent corn (Zea mays L.) production, but the degree of benefit is often unpredictable and may be related to tillage methods. This study investigated the effects of conventional-tillage (CT) and no-tillage (NT) on fertilizer replacement values for corn in a corn-soybean rotation. Field experiments were conducted for two growing seasons on two soils, a Ste. Rosalie clay (Humic Gleysol), and an Ormstown silty clay (Humic Gleysol). Continuous corn, corn following soybean, soybean 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, respectively) were compared. Tillage did not effect yield or N uptake consistently. Corn grain yields and N uptake were greater following soybean than following corn. Soybean provided N fertilizer credits ranging from 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 higher corn yields and lower previous winter precipitation resulting in greater NO3 carryover. Tillage effects on N credits from soybean differed between the sites. Consequently, N contributions of soybean to corn could not be related to tillage method or soil type. Key words:Zea mays L., Glycine max L. Merill, rotations, grain yield, N uptake, tillage, fertilizer N
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