A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Soil trace gas emissions influenced by pasture reformation systems in Rondônia,BrazilCaio Cesar Passianoto (1) , Toby Ahrens (2) , Brigitte Josefine Feigl (1) , Paul Steudler (2)(1) Centro de Energia Nuclear na Agricultura, CENA / USP, Caixa Postal 96, CEP13400-970, Piracicaba-SP ccpassia@cena.usp.br(2) The Ecosystem Center, Marine Biological Laboratory, Woods Hole, Massachusetts02543, U.S.A.Conversion of forest to pasture has been a major activity in the state of Rondônia, Brazilsince the 1970s. After decades of use, pasture productivity has declined. A number ofmanagement options exist to reform these lands including conventional tillage,fertilization, herbicide application, intermediate crop rotation, and planting of legumes.What are the consequences of these reformation practices for trace gas emissions? Asubset of these reformation practices has been studied in a large-scale field experiment(>3 ha) in an area of degraded pasture at Fazenda Nova Vida, Rondônia. The experimentinvolved five treatments: 1) control; 2) tilled; 3) herbicide; intermediate planting of no-till4) rice and 5) soybean. Here we report soil emissions of CO 2 , N 2 O, and NO from the firstthree months of control, conventional till, and no-till rice treatments. The tilled, herbicide,and rice treatments received 40, 40, and 12 kg N ha -1 , respectively. Tillage increased inCO 2 emissions by 35% over first 40 days, while herbicide application in the no-tilltreatment decreased CO 2 emissions by 20% over the first 30 days. Followingestablishment of the pasture grasses in the tillage and rice treatment, CO 2 emissions weresimilar to control plots. Tillage increased N 2 O emissions 17-fold, but highest emissionrates (357 ug m -2 hr -1 ) were measured after fertilizer application. A similar response wasmeasured after fertilizer application in the rice treatment. Tillage and fertilizer applicationresulted in increased NO emissions. Field measurements will continue to betterunderstand the longer term legacy of different reformation practices on soil gas emissionrates.