Urea and uan were side-dressed applied on the soil surface and incorporated (5-7 cm) to corn in a no-tillage system to study the balance of urea-N (15N) at harvest and measure the accumulated losses of NH3-N derived from these sources and from urea + KCl (solid) and uan + KCl (liquid), applied as 06-00-09 (N-P2O5-K2O) to the surface only. The treatments-originated from a factorial 1 + (2 x 2) + 2, with plot being + factorial 2 x 2 (two sources; urea and uan x two forms of application) + two additional treatments, urea + KCl mixture (solid) and uan + KCl (liquid) - were arranged in a randomized block design with four replications. The experiment was conducted on a high clay soil (Typic Acrustox) from the savanna region at Novartis Research Center - Seeds in Uberlândia (MG). Nitrogen treatments (approximately 100 kg ha-1) were side-dressed at 6-8 leaf phase of corn growth. The accumulated losses of NH3-N 26 days after N had been applied, showed that surface applications were of 54, 41, 17 and 14% for urea, urea + KCl, uan and uan + KCl, respectively. When urea and uan were incorporated into the soil, the N accumulated losses were 5.0 and 3.5% from the total N applied. At harvest, the amount of urea-N from urea accumulated in the plant (root + stalk + leaves + grain) was 19.9 kg ha-1 (or 20.8% of applied N) and 29.5 kg ha-1 (or 29.5% of applied N) when N was applied and incorporated to the surface, respectively. It was observed that 11.4 kg ha-1 (26.1%) was accumulated by the plant from urea-N of uan when uan was applied to the surface and 11.7 kg ha-1 (26.8%) when incorporated. The immobilized urea-N from surface and incorporated urea in the soil (0-45 cm) was of 9.9 kg ha-1 (10.0% of applied N) and 3.3 kg ha-1 (7.6% of applied N) from urea-N of uan. The amount of mineral N present in the soil derived from urea-N of urea and uan in the profile 0-150 cm, was 2.4 and 3.2%, respectively, of the total N applied to the surface and 5.9 and 2.5%, when incorporated. The global N balance indicated that 13.7 and 50.3% from urea-N were not recovered when applied to the surface and incorporated, respectively, and 47.7 and 57.6% of urea-N from uan, was not recovered in the soil-plant system.
no-tillage; immobilization; nitrogen plant recovery; lixiviation; corn; urea; uan; volatilization of NH3-N