Abstract

Field research was conducted at upstate Missouri to evaluate the impact of weed management systems and pre-plant nitrogen source selection [polymer-coated urea, (PCU); anhydrous ammonia (AA), urea, and ammonium nitrate (AN)] and side dressed urea ammonium nitrate (UAN) at 168 kg N ha^-1 on no-till corn grain yield and weed growth. Small-seeded broadleaf weed heights responded differently to PCU and anhydrous ammonia in the two years of study. Corn heights were greater with AN and urea compared to PCU, AA, and side dressed UAN 7 to 9 weeks after planting. Nitrogen fertilizer source selection and weed management system affected total weed biomass (giant foxtail, common waterhemp, and common lambsquarters) at physiological maturity of corn. However, these factors showed no interactive effect on corn grain yields. An early postemergence application of atrazine + dimethenamid-P + glyphosate reduced total weed biomass 86% and 92% compared to atrazine + dimethenamid-P applied preemergence following AA and the non-fertilized control, respectively. A two-pass postemergence system (glyphosate followed by glyphosate) had 74 to 79% greater weed biomass compared to residual systems when following PCU. All weed management systems increased yield 1.5 to 5.09 Mg ha^-1 compared to the non-treated control, and no yield difference was observed among weed management systems. PCU, AA, and side dressed UAN are preferred over broadcast urea for integrated weed management of no-till corn production in this region.

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