Recovery of Point-Injected Labeled Nitrogen by Corn as Affected by Timing, Rate, and Tillage

Point-injection technology is being developed to improve fertilizer management, particularly N management. This study was conducted to evaluate the effects of the rate (number) and timing of point-injections of an ammonium nitrate (NH₄NO₃) solution on N uptake and corn growth and to measure any differences due to tillage. Nitrogen-15 depleted NH₄NO₃ (AN) was hand-injected beside individual plants at the V1, V5, and/or V9 growth stages at rates of 50, 100, and/or 200 kg N ha⁻¹ with fall moldboard plow (MP), fall chisel plow (CP), and ridge-till (RT) systems. While MP had the highest grain and total dry matter production (but with the lowest N concentrations in those materials), tillage was not a significant factor in either the percentage of the total plant N derived from labeled AN (NF) or its recovery (NR) for any stage sampled. Generally the year (i.e. different environmental conditions) and application timing or a timing-by-year interaction had the greatest influence on NF and NR. Although plants sampled at the V9 stage on the average recovered more N from the V1 application (39%) vs the V5 application (27%), at maturity NR values for grain (35%) and total dry matter (47%) were the same for both V1 or V5 applications (when only two applications were made). However when three applications were made (at the V1, V5, and V9 stages), NR values decreased with time of application for both grain (38, 31, and 26%, respectively) and total dry matter (53, 43, and 33%, respectively). Across application timing, grain NR values were 34 and 31%, respectively, for MP and RT. Compared with preplant knifed-in labeled N for MP and RT systems in an adjacent simultaneous study, grain NR values for point-injected N in this study were 16 and 6% greater, respectively, indicating that multiple injections of fertilizer N improved N-use efficiency. Joint contribution: The National Soil Tilth Laboratory, and Journal Paper no. J-14071 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project no. 2445.