NITROGEN MANAGEMENT IN FURROW-IRRIGATED, RIDGE-TILLED CORN

Use of conservation tillage methods, including ridge-tillage, increase s crop residue cover which can increase loss of urea-based fertilizers . Objectives of this study were to evaluate N sources, rates, methods, and times of application for ridge-tilled, furrow-irrigated corn (Zea mays L.) on a Crete silt loam soil (fine, montmorillionitic, mesic Pa chic, Argiustoll) near Scandia, KS. When averaged over 5-yr, grain yie lds were less with urea-ammonium nitrate (UAN) broadcast and dribbled treatments than with anhydrous ammonia (AA) preplant knifed, 28% UAN s olution preplant knifed, and split applications of UAN knifed or dribb led. Surface dribbled UAN proved to be no more effective than surface broadcasting. Split applications of dribbled UAN gave greater yields t han a single preplant dribble application. Grain yields were unaffecte d by splitting knife applications of UAN. No differences occurred in g rain yield, grain N concentration, or amount of N removed in the grain between the AA and the UAN knife-injected treatments. Yield was unaff ected by application method x N rate interactions. Higher N rates did not compensate for more inefficient application systems. Corn grain N concentration and grain N removed followed the same trends as grain yi elds. Maximal grain yield, regardless of application treatment, was ac hieved with 158 lb N/acre. In April of 1990 and 1991, total amount of residual soil nitrate N was greater in plots receiving annual applicat ions of 200 lb N/acre than in plots receiving 50 or 100 lb N/acre. In 1991, plots that received knife-injected N at the 200 lb/acre rate con tained much more nitrate-N than plots in which N was surface applied, indicating that immobilization of N within the crop residue or some vo latilization losses could have occurred.