HR: 16:00h
AN: B24A-01    [Abstracts]
TI: Effect of Tillage and Non-tillage Agricultural Practice on Nitrogen Losses as NO and N2O in Tropical Corn Fields at Guarico State, Venezuela.
AU: * Marquina, S
EM: smarquin@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Rojas, A
EM: alrojas@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Donoso, L
EM: edonoso@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Rasse, R
EM: rrasse@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Giuliante, A
EM: apompett@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Corona, O
EM: ocorona@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AU: Perez, T
EM: tperez@ivic.ve
AF: IVIC, Atmospheric Chemistry Lab. IVIC. Aptdo 20632, Caracas, 1020A, Venezuela
AB: We evaluated the effect of agricultural practices on NO and N₂O emissions from corn fields at Northern Guárico, one of Venezuelan largest cereal production regions. Historically, the most common agricultural practice in these regions has been mono cropping. Tillage (T) and non-tillage (NT) of soils represent approximately 30 and 70% of the planted area, respectively. Comparative studies of the nitrogen losses associated with these agricultural practices are not available for these regions. This study was conducted at the farm "Tierra Nueva", Guárico State (9° 23' 33'' N, 66° 38' 30'' W) in two corn fields under tillage and non-tillage agricultural practice during the growing season (June-August 2006). A dry tropical forest, the primary ecosystem of the region, was evaluated for the same period of time. The corn and the forest fields were adjacent; therefore, they were exposed to the same meteorological conditions. The mean annual precipitation of the area is 622±97.3 mm (last 5 years). The soils are Vertisols (Typic Haplusterts). Nutrient soil concentrations (as nitrate and ammonium), water soil content and pH soil were measured in the fields for the same period of time. Soils were fertilized and planted simultaneously by a planting machine provided with a furrow opener where the fertilizer and seeds are incorporated between 0-10 cm depths. Tillage soils were fertilized on June 1st 2006 with 65 kgN/ha of NPK (13:18:16/3MgO, 3S; N as NH₄Cl), whereas non-tillage soils were fertilized the next day with 56 kgN/ha of NPK (12:25:12/3MgO, 3S; N as NH₄Cl). Second fertilization of both fields was done thirty-seven days later by broadcast adding 58 kgN/ha approximately, using nitrophosphate as fertilizer (NP 33-3: 33% N total; 16.7% N- NO₃^- and 16.6% N- NH₄⁺). In general, NO and N₂O soil emissions from both corn fields increased after fertilization events, and depend on water soil content and nutrient soil concentration. N₂O soil emissions were 11 and 9 times larger in comparison to the forest values for the 60-day evaluation period for NT and T, respectively. On the other hand, NO soil emissions were 1.5 and 5 times larger in NT and T fields, respectively, in comparison to forest values. The fertilizer-induced emissions factors (FEI) for NO and N₂O show that the nitrogen gaseous losses are mostly in the form of N₂O for NT (NO-FEI = 0.2% and N₂O-FEI=3.6%) and T (NO-FEI=1.7% and N₂O- FEI=2.8%) practices. However, NO losses are higher in T than NT soils, probably due to the higher porosity in the former that promotes NO production under aerobic conditions. These results imply that tillage agricultural practice leads to a higher stimulation of these nitrogen gaseous emissions than non-tillage agricultural practice. Our N₂O-FEI values for direct emissions are higher than the proposed by the IPPC national guidelines 2006 (FEI = 1%, Volume 4, Chapter 11). This implies that tropical agroecosystems are more susceptible to increase emissions after fertilization than temperate regions. Our results will be used to produce better estimates of direct N₂O emissions from tropical agriculture and improve the current Venezuelan national greenhouse gas inventory.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting