Nitrogen Balance as Affected by Application Time and Nitrogen Fertilizer Rate in Irrigated No‐Tillage Maize

High N requirements of no‐tillage maize ( Zea mays L.) make it imperative to develop management strategies that optimize crop production and N use efficiency (NUE). A 4‐yr field experiment was conducted at Balcarce (37°45′S, 58°18′W), Argentina, on a Typic Argiudoll and a Petrocalcic Paleudoll. The objective was to evaluate the effect of urea rate (0, 70, 140, and 210 kg N ha −1 ) at planting (FPL) or six‐leaf stage (FV6) on NH 3 volatilization, denitrification, soil residual nitrate, soil microbial biomass N (MBN), N uptake, grain yield, and unaccounted N (UN). Grain yield was 10.5 and 11.2 Mg ha −1 , and N uptake at physiological maturity was 168 and 192 kg N ha −1 (average of N rates) for FPL and FV6, respectively. Gaseous N losses ranged from 7.6 to 13.8% of applied N and were not affected by the fertilizer time. Relative to unfertilized control, fertilized treatments increased MBN (13.4 kg N ha −1 ) similarly for both fertilization times. For FPL, UN was 55, 69, 86, and 103 kg N ha −1 for 0, 70, 140, and 210 kg N ha −1 , respectively. For FV6, UN was 55, 46, 49, and 34 kg N ha −1 for 0, 70, 140, and 210 kg N ha −1 , respectively. The losses were attributed to nitrate (NO 3 ) leaching. Results of this experiment show that high fertilizer NUE in combination with economically competitive grain yields can be obtained when N is applied at V6 because gaseous N losses are low (less than 13.8%) and NO 3 leaching would be reduced.