EMISSIONS OF NOx AND N 2 O FROM OXISOL CULTIVATED WITH COTTON IN THE CERRADO REGION, BRAZIL rika Fernandes (CEFET/BA - UnB) Mercedes Bustamante (UnB) Alessandra Kozovits (present address UFOP) Richard Zepp (EPA) - ~2 millions km of the central Brazilian Plateau. - Correspond ~24 % of the country's area - The second largest of Brazil's major biomes - Seasonal rainfall (total: mm): - Wet season (October to April) - Dry season (May to September) - The soils are dystrophic: - 46 % are Oxisols (Latossolos) (clayey soils but well-drained, acidic, high Al saturation and low CEC) Cerrado (tropical savana) - overview Land use in the Cerrado Region s: The construction of Brasilia improved transportation and infrastructure in Central Brazil s: There was an expansion of agriculture * development of crops adapted to soil * natural conditions for mechanized - Today, the Cerrado is the most important region for grain and meat production in Brazil Exported products Original Cerrado area In 2002 the Cerrado veg. is fragmented Value of exportation from the Center-west in 2001 US$ 2,5 Billions Of this total, the following products contributed with ~76%, In decreasing order: In decreasing order: Product % Soybean (grain) 41,48 Soybean related products 21,39 Meat (frozen) 7,32 Meat (fresh) 3,25 Cotton 2,41 TOTAL 75,85 Fonte: IBGE 2000/SCO-MI Ministrio da Integrao Nacional Secretaria de Desenvolvimento do Centro-Oeste - Federal state of Goias (GO) (an area of old agricultural occupation) ha ha (4 x) - Federal state of Mato Grosso (MT) (a new agricultural frontier) 1990 ha ha (10 x) Source: Brazilian Ministry of Agriculture Evolution of the area with cotton GO MT Nitrogen management Cotton x soybean Cotton cultivation in the Cerrado is an option to soybean In many cases, used in rotation with soybean However, Cotton demands N fertilization ( kg N per hectare) While soybean does not demand N fertilization (N is supplied by biological fixation) Land use changes associated with fertilization may have important consequences for the soil- atmosphere exchange of NOx and N 2 O emissions Objective As there are few data on NOx and N 2 O fluxes in Cerrado region agroecosystems Here, we will report data on NOx and N 2 O emissions from a Oxisol planted with cotton under no till management under Brachiaria straw The study was carried out at the Pamplona Farm, located in Cristalina GO, Brazil (16 15` 02`` S and 47 37` 02`` W) Central part of the Cerrado region Braslia GOIS MG TO BA MT MS Study site. Cristalina Study site: - Cotton field - Native cerrado (a control site) Study period: - November/2004 to August/ N emissions were measured monthly - wet and dry season Methodology Cultivation phases: - before planting - planting with row fertilization 24 kg N ha -1 as di-ammonium phosphate - surface fertilization 36 kg N ha 1 as ammonium sulfate 90 kg N ha 1 as urea - Along the growing season - before and post harvest Before planting Before harvest In the crop rows 5 m 10 m Methodology Between the crop rows chamber (PVC) Sampling site: N oxides measurements Soil surface fluxes of NO and N 2 O were measured using polyvinyl chloride (PVC) chambers; NO was analyzed using a Scintrex LMA-3; The N 2 O samples were collected using 60 mL polypropylene syringes and analyzed with a gas chromatograph (Shimadzu GC-14A); Statistical tests were used to make comparisons among: cultivation phases; cultivation phases and native cerrado. 1.Fluxes before planting were very variable probably because of Brachiaria straw 2. However, there was no difference between fluxes before planting and after planting with row fertilization with di-ammonium phosphate (24 kg N ha -1 ) NO fluxes 3. Slightly higher NO emissions were measured four hours after surface fertilization with ammonium sulfate (36 kg N ha -1 ) - In the crop rows (6 X) - Between the crop rows (2 X) 4. A large pulse of NO was observed 3 days after the third fertilization when 90 kg N ha 1 were applied: Pulse = 39,3 20,1 ng N cm -2 h -1 (In the crop rows) Pulse = 83,3 11,9 ng N cm -2 h -1 ( Between the crop rows) NO fluxes 5. In cultivation phases after fertilizations, NO fluxes in the cotton field were similar to fluxes in the native cerrado N 2 O fluxes - Most of the N 2 O fluxes measured were very low and under the detection limit (0.6 ng N 2 O cm -2 h -1 ) NO 3 - N2N2 NH 4 + NO N2ON2O N2ON2O Hole-In-The-Pipe Model Firestone and Davidson 1989 Nitrification Denitrification Ratio of NO / N 2 O fluxes explained by 2 factors: 1. During the period of the study, ammonium predominated over nitrate probably contributing to higher NOx emissions than N 2 O emissions 2. Additionally, During the study period, WFPS ranged from 15 to 51 % Nitrification rates are often elevated in aerobic conditions as when WFPS < 60% NO / N 2 O fluxes % WFPS control on N oxide emissions Davidson, 1991 Conclusions Application of nitrogen fertilizers resulted in elevated NO emissions compared to background levels in the native cerrado. This increase was a result of pulses after N additions; NO fluxes might be influenced by type of fertilizers and amount of N used; Total N-NO emission for the cultivation period (258 days) was 0.8 kg.ha -1 corresponding to 0.5 % of the N applied as fertilizer (150 kg.ha -1 ). Funding NASA / MCT - Experimento de Grande Escala Biosfera- Atmosfera na Amaznia (LBA) ND-07 Acknowledgments Pamplona Farm (SLC Company) Thanks rika Fernandes,Mercedes Bustamante,Alessandra Kozovits Richard Zepp