RIDGE-TILLAGE CORN RESPONSE TO POINT-INJECTED NITROGEN-FERTILIZER

Management practices to improve N-use efficiency have been studied repeatedly for conventional tillage and no-till systems. Little work has been done, though, to identify efficient N-placement methods for ridge-tillage systems. The objective of this study was to test the hypothesis that point injection of N in the ridge can optimize N-use efficiency and corn (Zea mays L.) production in ridge tillage, compared with broadcast N or injection between rows. Corn-soybean [Glycine max (L.) Merr.] rotation studies were conducted between 1986 and 1988 on Webster and Marna silty clay loams (fine-loamy, mixed, mesic Typic Haplaquoll and fine, montmorillonitic, mesic Typic Haplaquoll, respectively). Treatments consisted of a control (no N) and factorial combinations of three N-placement methods (broadcast, point injection between rows, or point injection in rows) and five rates (22, 45, 67, 112, and 157 kg N ha-1) applied as urea-NH4NO3 solution (UAN). Fertilizer-N recovery by plants was determined at four growth stages in labeled-N microplots. Corn yields, percentage of N derived from fertilizer, and percentage of fertilizer N recovered were significantly greater with injected N than with broadcast N. Injection position generally did not affect plant response. Point injection of N fertilizer can improve N-uptake efficiency over broadcast methods in ridge-tillage corn, but the importance of injection position was not substantiated.