Illinois Fertilizer & Chemical Association
Supply · Service · Stewardship

Nitrogen Management of Corn as Affected by Timing of Weed Control and Nitrogen Application

S. A. Ebelhar, B. G. Young and R. F. Krausz
No-tillage corn production in southern Illinois continues to be challenging with weed control problems and higher nitrogen (N) losses than conventional tillage systems. If weeds are not controlled on a timely basis, they could compete with corn for nutrients and water. Much of the work with weed control timing has dealt with single N rates of application. For this reason it has been difficult to determine the optimum economic N rate and to determine the effects on N use efficiency at this optimum rate. It is suggested that farmers control weeds in no-tillage systems before the weeds reach 4" of growth (Bryan Young, Southern Illinois University, personal communication), but often logistical problems and weather delays prevent this from occurring. Failure to control weeds on a timely basis sets up an unhealthy competition between weeds and corn for nitrogen and water.
No-tillage systems have a propensity for poor nitrogen utilization unless the N can be applied at sidedress. While this can prevent much of the N losses often seen with early and preplant N application, and reduce the N availability to weeds, it does create more competition among the weeds and early corn for what little N might be available prior to sidedressing. The objectives of this study were to 1) evaluate the effect of weed competition on corn grain yields and N use efficiency, 2) determine the effect of timing of N application on impacts of weed competition, and 3) evaluate the interactions of weed control and N timings.