Denitrification in maize under no-tillage:: Effect of nitrogen rate and application time

Denitrification N losses from soils under no-tillage (NT) can reduce N-use efficiency and destroy the ozone layer if appreciable amounts of N oxides (N2O, NO) are lost. The objective of this study was to evaluate the effect of surface-applied area rate (0, 70, and 210 kg N ha(-1)) and different application times [planting (PL) and six-leaf stage (V6)] on denitrification losses (DLs) in NT irrigated maize (Zea mays L.). The field experiment was carried out in the 1996 and the 1998 growing seasons, at Balcarce (37 degrees 45'S; 58 degrees 18'W), Argentina, on a Typic Argiudoll and a Petrocalcic Paleudoll. The annual mean rainfall in the area is 870 min and annual mean temperature is 13.7 degreesC. Denitrification rates (DRs, N2O) were measured Using C2H2 blockage core method. The DRs were highest between PL and the V6 because of higher water filled pore space (WFPS), and were closely associated with the WFPS (r(2) equal to 0.66 and 0.76 for 1996 and 1998, respectively). On average, accumulated DLs for the PL application were 7.6 and 9.8 kg N2O-N ha(-1) (5.5 and 2.6% of N applied for 70 and 210 kg N ha(-1), respectively). However, for application at the V6, accumulated DLs were 2.0 and 2.1 N2O-N kg ha(-1) (1.0 and 0.4% of N applied for 70 and 210 kg N ha(-1), respectively). The results indicate that for this soil and climatic zone, denitrification N losses were greater when the fertilizer was applied at PL than when fertilizer was applied at the V6.