Palavras AbstractThe technique of eddy correlation was used to measure the net ecosystem exchange over a woodland savanna (Cerrado Sensu stricto) site (Gleba Pé de Gigante) in southeast Brazil. The data set included measurements of climatological variables and soil respiration using static soil chambers. Data were collected during the period from 10 to as much as 50 kgC ha day . The annual NEE sum appeared to be nearly in balance, or more exactly a small sink, equal to -1 -1 0.1 0.3 tC ha yr , which we regard possibly as a realistic one, giving the constraining conditions imposed to the turbulent flux calculation, and favourable hypothesis of succession stages, climatic variability and CO fertilization. Agosto) e na estação chuvosa, respectivamente, por um padrão de sensível correlação com a temperatura (Q =4.9) e 10 umidade do solo. Com base nos fluxos atmosféricos de CO , a PLE mostrou uma variabilidade no ciclo diurno grandemente 2 controlada pela radiação solar, umidade e temperatura do ar. Na escala sazonal, a umidade do solo foi uma variável de alta correlação com a PLE, que aparentemente induziu a queda de folhedo, redução da atividade fotossintética e da respiração -do solo. O sinal da PLE foi negativo (sumidouro) na estação chuvosa e no início da estação seca, com taxas de -25 kgChadia , e máximos de até 40 kgCha dia . Na estação seca o sinal foi positivo (emissão), o que foi revertido logo no início das chuvas. No fim da estação seca, em dias de grande estresse hídrico, ainda observou-se a resposta da fotossíntese na escala do ecossistema, mesmo tendo sido positiva a PLE. Paralelamente ao decorrer da estação seca, a PLE progressivamente

Resumo -A mineralização do N orgânico é um dos principais fatores que determinam as quantidades de lodos de esgoto (LE) a aplicar em solos. O objetivo deste trabalho foi quantificar, em laboratório, o potencial de mineralização de N orgânico num Latossolo Vermelho distroférrico, tratado com dois LE anaeróbios, um de origem estritamente urbana (Franca, SP) e outro com presença de despejos industriais (Barueri, SP). Os LE foram aplicados ao solo em doses de 1,5, 3, 6 e 12 g kg -1 (Franca) Termos para indexação: Latossolo, acidificação, pH, condutividade elétrica. Nitrogen mineralization in a tropical soil amended with sewage sludgesAbstract -Mineralization of organic N contained in sewage sludges is a key factor in determining the rates of these materials to be applied to agricultural soils. This work aimed at quantifying the potential of mineralization of the organic N in an Oxisol treated with two anaerobically-digested sewage sludges (one derived from strictly urban sewage -Franca, São Paulo State, Brazil -, and the other from a mixture of urban and industrial sewages -Barueri, São Paulo State). The sludges were applied at four rates: 1.5, 3, 6 and 12 g kg -1 (Franca), and 4, 8, 16 and 32 g kg -1 (Barueri), and the incubation period, was 15 weeks. Net inorganic N accumulation in the soil measured at the end of the incubation period was proportional to the rate of organic N applied as sludges. The potential of mineralization estimated by the single exponential model for the soil without sludge was 24 mg kg -1 of N, and ranged from 44 to 265 mg kg -1 of N, for the sludge-treated soil. The fraction of potential mineralization of the organic N contained in the sludges was estimated in 31%. N mineralization was slower in the soil treated with the two higher rates of the Barueri sludge. Sewage sludges caused soil acidification; Franca sludge was more effective in this way than Barueri sludge.Index terms: Latosol, acidification, pH, electrical conductivity.(1) Aceito para publicação em 9 de julho de 2002.(2) Embrapa-Centro Nacional de Pesquisa de Monitoramento e Avaliação de Impacto Ambiental, Caixa Postal 69, CEP 13820-000 Jaguariúna, SP. E-mail:rcboeira@cnpma.embrapa.br, ligo@cnpma.embrapa.br, dynia@cnpma.embrapa.br IntroduçãoEm virtude da poluição provocada por lançamen-to de esgotos in natura em cursos d'água, estações de tratamento de esgoto vêm sendo implementadas nas principais cidades brasileiras, obtendo-se, geralmente, considerável redução da carga orgânica dos efluentes. No entanto, as estações de tratamento de esgoto defrontam-se com novo problema: a destinação a ser dada ao lodo de esgoto, resíduo que permanece após o tratamento dos esgotos. Diversas alternativas têm sido buscadas, entre elas a utilização de solos como meio de descarte para o lodo, situação em que há risco de poluição ambiental, com possibilidade de contaminação da cadeia alimentar com diversas substâncias e elementos nocivos.Utilizado com fins agrícolas, o lodo pode atuar como condicionador de solo, por sua elevada carga orgânica (40% a...

a b s t r a c tStudy region: The area of woodland savanna (cerrado) is located in southeast Brazil (21 • 36 to 44 S, 47 • 34 to 41 W). Study focus: The cerrado sensu-stricto savanna evapotranspiration was observed using the eddy-covariance method over three years. New hydrological insights for the region: The first year total rainfall (R = 1664 mm) was 11% above the long-term rainfall (1498 mm) and the total evapotranspiration (ET = 1242 mm) and water equivalent of available energy (A v = 1835 mm) were approximately 4% and 2% greater, respectively, than in the second year when the rainfall total was 5% lower than the long-term average. In the third year despite the total rainfall (1259 mm) being 24% lower than the first year and 16% lower than the average, the totals of ET (1242 mm) and A v (1815 mm) were approximately the same.The small variation in the observed annual ET totals shows that in this cerrado vegetation the deep soil moisture content supports the ET in a dry year and the water available for recharging the soil profile and groundwater (∼R − ET) was dominated by the rainfall amount being significantly greater in the wet year (422 mm) than in the dry year (13 mm).

The evapotranspiration (E) from a sugarcane plantation in the southeast Brazil was measured by the eddy-covariance method during two consecutive cycles. These represented the second (393 days) and third year (374 days) re-growth (ratoon). The total E in the first cycle was 829 mm, accounting for 69% of rainfall, whereas in the second cycle, it was 690 mm, despite the total rainfall (1353 mm) being 13% greater. The ratio of E to available energy, the evaporative fraction, exhibited a smaller variation between the first and second cycles: 0.58 and 0.51, respectively. The estimated interception losses were 88 and 90 mm, respectively, accounting for approximately 7% of the total rainfall. The sugarcane yield in the second cycle (61.5 ± 4.0 t ha À1 ) was 26% lower than the first cycle, as well as lower than the regional average for the third ratoon (76 t ha À1). The below average yield was associated with less available soil water at the beginning of the cycle, with the amount of rainfall recorded during the first 120 days of re-growth in the second cycle being 16% of that recorded in the first (203 mm).

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Reis. 2013. Fluxes of CO2 above a sugarcane plantation in Brazil.Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Fluxes of CO 2 were measured above a sugarcane plantation using the eddy-covariance 29 method covering two growth cycles, representing the second and third re-growth 30 (ratoons) harvested with stubble burning. The total net ecosystem exchange (NEE) in 31 the first cycle (second ratoon, 393 days long) was -1964±44 g C m -2 ; the gross 32 ecosystem productivity (GEP) was 3612±46 g C m -2 and the ecosystem respiration (R E ) 33was 1648±14 g C m -2 . The NEE and GEP totals in the second cycle (third ratoon, 374 34 days long) decreased 51% and 25%, respectively and R E increased 7%. Accounting for 35 the carbon emitted during biomass burning and the removal of stalks at harvest, net 36 ecosystem carbon balance (NECB) totals were 102±130 g C m -2 and 403±84 g C m -2 in 37 each cycle respectively. Thus the sugarcane agrosystem was approximately carbon 38 neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional 39 average (8.3 kg SFW m -2 ). Although it was a carbon source to the atmosphere, observed 40 productivity (6.2 kg SFW m -2 ) of the third ratoon was 19% lower than the regional 41 average due to the lower water availability observed during the initial 120 days of re-42 growth. However, the overall water use efficiency (WUE) achieved in the first cycle 43