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DIVISION S-8—NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Denitrification in Maize Under No–Tillage

Effect of Nitrogen Rate and Application Time

Facultad de Ciencias Agrarias (U.N.M.P.)-Estación Experimental Agropecuaria Balcarce (I.N.T.A.), Unidad Integrada Balcarce, C.C. 276, (7620) Balcarce, Buenos Aires, Argentina

* Corresponding author (E-mail: hecheverr{at}balcarce.inta.gov.ar)

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 urea 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°45'S; 58°18'W), Argentina, on a Typic Argiudoll and a Petrocalcic Paleudoll. The annual mean rainfall in the area is 870 mm and annual mean temperature is 13.7°C. 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 (r² 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.

Abbreviations: CT, conventional tilling, DL, denitrification loss • DR, denitrification rate • GLM, general linear model • LSD, least significat difference • NT, no-tillage • PL, planting • TF, treatment fertilized • V6, six-leaf stage • WFPS, water filled pore space

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