1. Trace gas emissions from the soil related to
land-use changes in the Cerrado region
1Kozovits, A.R., 1Viana, L.T., 1Sousa, D.M., 1Bustamante, M.M.C., 2Zepp, R.
1Departamento de Ecologia, Universidade de Brasília, , Brasília, DF.
2 Environmental Protection Agency, Athens - GA, USA
Results
Introduction
Highest NO soil emissions were found in the corn (Fig. 1 - A) and bean (B) areas compared to soybean (C) and native cerrado (D) areas. These emissions tended to accompan the status of available N in the soil. The net N mineralization dynamics were similar in the two legume crops (immobilisation before the planting and mineralization just after the fertilization). In the native area, there was net mineralization during the dry season and immobilisation with the onset of the rainy season (Fig. 2). Generally, N2O was under the detection limit (0.6 ng N2O cm-2 h-1). Higher values were observed in the cornfield just after N fertilization. In contrast to the N emissions, soil respiration from all studied sites seemed to be closely related to the soil moisture, tending to be higher in the crop areas (Fig. 1, A and B).
The atmosphere chemistry depends partially on biological processes related to trace gas production and destruction. Regarding to NOx, recent estimates indicate that, globally, soil microorganisms may release similar amounts these gases per year, as combustion sources. NOx emissions are mainly influenced by N availability, soil moisture, texture and temperature. Since agricultural management practices strongly alter many of these variables, it is expected that emissions in agricultural systems will differ from those in undisturbed areas. In this context, the effect of conversion of large native Cerrado areas into croplands on the magnitude and dynamics of soil trace gases emissions was investigated.
Figure1.Soil-atmosphere fluxes of NO, N2O and CO2 measured in corn (A), bean (B), soybean (C) and native cerrado (D) areas. The bars represent soil humidity (right axis). Red and black arrows represent planting and harvest dates, respectively. “F” indicates fertilization events.
(A)
(A) F F
(B)
(B) F F
(C)
(C)
(D)
(D)
Figure 2. Available soil NO3- and NH4+ and net N mineralization (0-5 cm).
OBS: NH4+ is on the right y-axis.
Material and Methods
Conclusions
Study site: Fazenda Dom Bosco, about 100 Km from Brasília.
Fluxes of NO, N2O and CO2, as well as soil moisture, available inorganic N and net mineralization rate were measured in areas planted (no-tillage) with: 1. corn, 2. soybean, 3. common bean and 4. in adjacent native Cerrado area.
Samples were taken in six points per area distant about two meters from each other. The gas fluxes were measured using PVC-chambers following the crop management (just before and after each fertilization) and also monthly during the growing season.
NO emissions increased with the replacement of native Cerrado areas by fertilized crops (corn and bean). Emissions from the soybean area were similar to the native Cerrado.
The agricultural systems in the Brazilian Savanna region may represent relevant contribuition to the regional and global trace gas budget (NO), especially considering the large land extension occupied by fertilized crops (about 1,983,291 ha for corn), (187,982 ha for bean ) and (476,472 ha for cotton).