NO AND N 2 O EMISSIONS RELATED TO THE NITROGEN FERTILIZATION IN A CORNFIELD

1. NO AND N2O EMISSIONS RELATED TO THE NITROGEN FERTILIZATION IN A CORNFIELD UNDER NO-TILLAGE AND TILLAGE SYSTEMS A.M.de Carvalho1,2; M.M.C.Bustamante2; A. R. Kozovits2; D. M. Sousa2; L. T. Viana2; L.N. de Miranda1 1 EMBRAPA-Cerrados, Rodovia Brasília Fortaleza BR 020 Km 18, 73301-970, Planaltina-DF, Brazil. 2 Department of Ecology, University of Brasília, 70.919-970, Brasília - DF, Brazil e-mail: arminda@unb.br INTRODUCTION Tillage practices can affect microbial community and, consequently, soil organic matter incorporation/mineralization and trace gas fluxes. The dynamic of nitrogen oxides emissions from Cerrado soils related to the nitrogen fertilization is still not well known, in spite of the intensification of agricultural activities in this region. The objective of this work was to investigate the short-term effects of nitrogen fertilization in a cornfield on NO and N2O emissions, under no-tillage and tillage systems, in the Cerrado region. RESULTS AND DISCUSSION NO flux (P < 0.0001) varied significantly with the time (Figure 1). Highest NO fluxes were found immediately (4.8 to 5.9 ng NO-N cm-2 h-1) and 3 days after N fertilization (4.4 to 5.2 ng NO-N cm-2 h-1). The lowest fluxes were found after five days (1.0 to 1.4 ng NO-N cm-2 h-1) which are similar to values obtained without fertilization in other corn plantations in the region. In general, the no-tillage plots tended to present higher fluxes soon after the N fertilization compared to the tillage plot. On the other hand, the tillage plots presented higher fluxes on the third day. Most of the N2O fluxes (Figure 2) were below the detection limit (0.6 ng N2O-N cm-2 h-1), except on the third day, when slightly higher emission (0.80 ng N2O-N cm-2 h-1) was observed in the tillage plots. Soil moisture and temperature (P < 0.0001) decreased with time (Figures 3 and 4). Concentration of N-NH4 (P < 0.005) showed significant changes with time (Figure 5) in similar pattern to the NO fluxes. There were no differences in the investigated parameters between the tillage and no-tillage systems probably because of the short implementation time of the systems (3 years).The results showed an immediate pulse in the NO emission after fertilization and irrigation, and a second pulse after three days. MATERIAL AND METHODS The experimental site, mucuna-preta/corn succession on a Oxisol, belongs to the EMBRAPA-Cerrados (Planaltina-DF). Associated with irrigation, 20 kg ha-1 N (at the sowing) and 60 kg ha-1 N-urea (cover – 20 days after the sowing) were applied. The experimental design used was random blocks, in no-tillage and tillage systems. The fluxes were determined immediately, one, two, three and five days after nitrogen cover. In each plot, fluxes of NO and N2O were measured in four and three PVC chambers, respectively.Repeated-measures analysis (split plot) were performed to compare the results. Figure 1. NO fluxes as a function of the N fertilization, in tillage and no-tillage systems. Figure 2. N2O fluxes as a function of the N fertilization, in tillage and no-tillage systems. Figure 4. Soil temperature during the study period Figure 3. Soil moisture during the study period CONCLUSIONS (i) An immediate pulse in the NO emission following fertilization and irrigation, and a second pulse after three days. (ii) After five days, the fluxes decreased to background levels. (iii) Most of the N2O fluxes were below the detection limit. (iv) There were no differences in the fluxes between the tillage and no-tillage systems . N-Figure 5. Inorganic nitrogen during the study period, in tillage and no-tillage systems.