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The use of N fertilizer in agriculture is considered an important source of atmospheric N2O and NOx. Choice of fertilizer type and management has been considered a method for mitigating these emissions. Micrometeorological methods were used to study the effect of inorganic N fertilizers urea (U), slow‐release urea (SRU), and ammonium nitrate (AN) on fluxes of N2O, NO, and NO2 from turfgrass field plots during three seasons, from 1995 to 1997 (total of 353 d of measurement). Daily average fluxes after fertilizations reached a maximum of 2091 ng N2O‐N m−2 s−1 after the first fertilization with AN in 1996. The fertilized plots had significantly higher emissions (P < 0.05) than the control plot, and the highest N2O emissions were from AN in 1995 and 1996, and from SRU in 1997. Daily fluxes of up to 186 ng NO‐N m−2 s−1 were measured within 1 wk following fertilization in 1997. The U plot had significantly higher NO emissions during all seasons compared with other fertilized plots. Fluxes of NOx during 1996 and 1997 were consistently downward, indicating that turfgrass was acting as a sink for NOx. NO2 uptake seemed to be directly related to NO emissions, and the U plot presented the highest NO2 uptake. Urea‐based fertilizers seem to minimize N2O emissions, although long‐term effects of SRU still need to be studied. The higher NO emissions from U‐based fertilized plots do not seem to be a problem, since NOx uptake occurred at higher rates than NO emission.

Rubber tree plantations may improve the soil's physical and chemical properties, and they may sequester atmospheric carbon in the biomass or the soil. However, the potential role of these plantations in sequestering carbon in the soil and plant biomass has not been fully evaluated. This study evaluated rubber tree plantations at Paranapoema, which is located in the northwestern region of the Paraná state of Brazil, to measure the biomass in plantations of different ages and to determine the organic carbon content and  13 C in the soils. Biomass accumulation was evaluated using the destructive method in plantations of different ages. The total carbon stock in the top 60 cm of the soil was 63.4 Mg C ha -1 for the pasture adjacent to the plantations and 66.8 and 79.3 Mg C ha -1 for the 4-and 15-year-old rubber tree plantations, respectively. These values are equivalent to an annual increase in soil carbon stocks of 0.85 and 1.06 Mg ha -1 , respectively, and they do not include the accumulation of carbon as tree woody biomass. The soil  13 C indicated a relatively fast conversion from the previous C4-C (pasture; Brachiaria-Urochloa brizantha) to C3-C (rubber tree). The results from this study suggest that rubber tree plantations have untapped potential to sequester carbon over a relatively short time period.Potencial de sequestro de carbono em seringais no noroeste do Paraná, Brasil RESUMO. O plantio de seringueiras é uma opção para melhorar as propriedades físicas e químicas do solo e promover o sequestro de carbono atmosférico, seja na biomassa ou no solo. Apesar das vantagens, o potencial de sequestro de carbono dos seringais no solo e na biomassa não foi ainda avaliado. Um estudo foi conduzido em seringais localizados em Paranapoema, na região noroeste do Paraná, com os objetivos de medir a biomassa em seringais de diferentes idades, e determinar o conteúdo de carbono e o  13 C do solo. O acúmulo de biomassa foi avaliado pelo método destrutivo em seringais de diferentes idades. O estoque total de carbono até 60 cm do solo foi de 63,4 Mg C ha -1 na pastagem adjacente aos seringais, 66,8 e 79,3 Mg C ha -1 nos seringais de 4 e 15 anos de idade, respectivamente, equivalendo a uma taxa anual de aumento de carbono no solo de 0,85 e 1,06 Mg ha -1 , sem considerar o acúmulo de carbono pela biomassa da planta. Os valores de  13 C do solo indicaram uma conversão relativamente rápida do carbono proveniente de plantas C4 (pastagem, Brachiaria-Urochloa brizantha) para carbono de plantas C3 (seringal). Os resultados deste estudo indicam o grande potencial de seringais em sequestrar carbono em um período relativamente curto.Palavras-chave: seringueira, Hevea brasiliensis,  13 C do solo, razão isotópica, estoque de carbono no solo.

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[1] An attenuated eddy covariance (AEC) method is proposed, combining the use of a relatively robust three-dimensional sonic anemometer and a ventilated capacitive hygrometer-thermometer (CHT). The CHT is able to resolve a large enough frequency region of the water vapor density turbulent fluctuations to allow corrections for its limited time response in the inertial subrange of the vertical velocity-humidity cospectrum. This approach is often called the ''band-pass covariance method.'' In the present work we propose a technique in which the covariance between the vertical velocity and water vapor density fluctuations is calculated directly in the time domain (as in the standard eddy covariance technique) and then corrected for the effects of wind velocity and sensor temperature. This technique has been tested with the capacitive sensor ''uncapped'' and ''capped'' and in both cases compares well (RMSE 23 W m À2 ) with eddy covariance measurements using fast response hygrometers.

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