O presente trabalho teve como objetivo testar a utilização conjunta do TDR (Reflectometria no Domínio do Tempo) e do tensiômetro, na determinação da curva de retenção de água no solo. Foram determinadas várias curvas de retenção de água de um solo franco-arenoso, em condições de laboratório e campo, em solo peneirado e em solo com estrutura indeformada, com a utilização dos métodos TDR-tensiômetro e placa de Richards. Os valores de umidade volumétrica do solo determinados com o método TDR-tensiômetro, foram menores que os obtidos com o método placa de Richards. As leituras de umidade volumétrica do solo franco-arenoso realizadas com o TDR, necessitam de correção.<br>TDR (Time Domain Reflectometry) and tensiometer methods were used to obtain soil water retention curve. Several soil water retention curves of a sandy loam soil were determined in both laboratory and field conditions from sieved and undisturbed soil using a TDR-tensiometer and Richard's pressure plate apparatus. The values of soil water content determined by TDR-tensiometer were smaller than those achieved by Richard's pressure plate. The TDR's data of the soil water content for this sandy loam soil require specific correction.

O presente trabalho teve como objetivo testar a utilização conjunta do TDR (Reflectometria no Domínio do Tempo) e do tensiômetro, na determinação da curva de retenção de água no solo. Foram determinadas várias curvas de retenção de água de um solo franco-arenoso, em condições de laboratório e campo, em solo peneirado e em solo com estrutura indeformada, com a utilização dos métodos TDR-tensiômetro e placa de Richards. Os valores de umidade volumétrica do solo determinados com o método TDR-tensiômetro, foram menores que os obtidos com o método placa de Richards. As leituras de umidade volumétrica do solo franco-arenoso realizadas com o TDR, necessitam de correção. | TDR (Time Domain Reflectometry) and tensiometer methods were used to obtain soil water retention curve. Several soil water retention curves of a sandy loam soil were determined in both laboratory and field conditions from sieved and undisturbed soil using a TDR-tensiometer and Richard's pressure plate apparatus. The values of soil water content determined by TDR-tensiometer were smaller than those achieved by Richard's pressure plate. The TDR's data of the soil water content for this sandy loam soil require specific correction.

Avaliaram-se as alterações na quantidade e qualidade dos poros de um Latossolo-Amarelo álico coeso, do ecossistema Tabuleiros Costeiros, em função do uso (citros, mandioca e mata) com base nas curvas de retenção do solo, determinadas com 10 repetições em amostras de solo com estrutura indeformada, coletadas aleatoriamente na profundidade de 0,10 e 0,30 m, em cada tratamento. As tensões aplicadas foram de 0,5; 1; 2 e 5 kPa em funil de placa porosa e 30, 70, 100, 500 e 1500 kPa em câmara de pressão, também com placa porosa. Os resultados de cada tensão foram avaliados pelo teste de Tukey, a nível de 5% de probabilidade e, para fins de cálculo da condutividade hidráulica relativa, os valores de umidade versus tensão foram ajustados à equação de van Genuchten. Verificou-se que houve redução da macroporosidade do solo com o cultivo e o manejo na cultura de citros; além disso, constatou-se, ainda, que o uso do solo com mandioca aumentou a capacidade de água disponível do solo a 0,10 m de profundidade, em relação ao citros. Também relevante e que depreende dos resultados, é o fato de que, no citros, o manejo compactou o solo de maneira mais intensa que na mandioca, levando o solo, com esse cultivo (citros) a reter menos água que a mata a baixas tensões e mais água que a mata a altas tensões. A condutividade hidráulica relativa foi sempre inferior para o citros, fato que, aliado à macroporosidade inferior, faz com que se conclua que o solo com citros apresenta valores de condutividade hidráulica sempre inferiores que os da mata e mandioca.<br>Modifications in the quantity and quality of soil pores of a "Latossolo Amarelo alico" located in the Brazilian tableland ecosystem under three circumstances (natural forestry, cropped to citrus and cropped to cassava) were evaluated through analysis of water retention curves. These were determined with 10 replications using undisturbed soil samples (randomly collected in each treatment) submitted to tensions of 0.5, 1.0, 2.0, and 5.0 kPa (porous plate funnels) and 30.0, 70.0, 100.0, 500.0 and 1500.0 kPa (porous plate pressure chambers). After the application of the Tukey test at the level of 5% of probability to the results, it was possible to verify that there was a decrease of the soil macroporosity in the soil cropped under citrus. This fact, in association with the determination of the relative soil hydraulic conductivity, leads to a strong tendency that the soil with citrus presents hydraulic conductivity values always smaller than those for the soil with forestry and cassava. It was also verified that the soil, when cropped to cassava, increased its soil water holding capacity at the 0.10 m soil depth, in comparison with the soil cropped to citrus. A fact also relevant from the results was that the citrus soil management compacted more intensively the soil than the cassava one; this caused a lesser water retention in the soil under citrus than the soil under forestry at lower soil water tensions and more water retention than the forestry at higher tensions.

Abstract Soils are one of the largest terrestrial pools of carbon, yet there is still little understanding of spatial variability for ecosystems in the tropics. Fire plays an important role in Neotropical savannas ecosystems and significantly contribute to global greenhouse gas (GHG) fluxes. Nevertheless, the impacts of burning on soil carbon is still uncertain in Latin America. We compared soil organic carbon (SOC) in the first 20 cm depth in savannas in pre and post fire conditions along a forests-savanna edge typically present in these landscapes of the northern South America. We established 8 transects of 20 m longitude along the border with 1m2 plots sampled every 4 m. SOC pre-disturbance was on average 1.794 (±SE 0.043) and the minimum value found (1.08%) was registered 6 months after the burning. Our results show that both the influence of the distance to the edge and the time of burning affect negatively the SOC and also there is a significant interaction between both variables. Our results provide improved estimates of the effect of fire on soil carbon stocks and its highly dynamic nature. We believe these finding will be a step to help better estimate GHG in this type of heterogeneous landscapes. Further it provides a tool for understanding C dynamics under a climate change context with predicted increased fire frequency, extent and severity. | Resumen Los suelos son una de los mayores reservorios terrestres de carbono, sin embargo, todavía hay poca comprensión de su variabilidad espacial en los ecosistemas tropicales. El fuego juega un papel importante en los ecosistemas de sabanas neotropicales y contribuye significativamente a los flujos de gases de efecto invernadero (GEI). A pesar de ello, los impactos derivados de las quemas de carbono en el suelo son todavía muy inciertos en América Latina. En este estudio se comparó el carbono orgánico del suelo (COS) en los primeros 20 cm del suelo en las sabanas de la Orinoquía en Colombia en condiciones previas y posteriores a la ocurrencia de una quema a lo largo de un borde en la interfase bosques-sabana presente en estos paisajes del norte de Sudamérica. Se establecieron 8 transectos de 20 m de longitud a lo largo del borde entre el bosque y la savana y se crearon parcelas de 1m2 muestreadas cada 4 m. El COS en transectos pre-perturbación fue en promedio de 1,794 (± SE 0.043) y el valor mínimo encontrado (1,08%) se registró 6 meses después de la quema. Nuestros resultados muestran que el SOC es superior en el interior del bosque y que existe tanto una influencia de la distancia desde su borde y del tiempo desde la quema que afecta al COS. También hay una interacción significativa entre ambas variables. Nuestros resultados proporcionan valiosa información para mejorar las estimaciones de los efectos del fuego sobre las existencias de carbono en el suelo y ayudarán a una mejor estimación de GEI en este tipo de paisajes heterogéneos. Además se proporciona una herramienta para la comprensión de la dinámica del carbono en un contexto de cambio climático con el posible aumento de la frecuencia de incendios, extensión e intensidad de estos.

Soils are one of the largest terrestrial pools of carbon, yet there is still little understanding of spatial variability for ecosystems in the tropics. Fire plays an important role in Neotropical savannas ecosystems and significantly contribute to global greenhouse gas (GHG) fluxes. Nevertheless, the impacts of burning on soil carbon is still uncertain in Latin America. We compared soil organic carbon (SOC) in the first 20 cm depth in savannas in pre and post fire conditions along a forests-savanna edge typically present in these landscapes of the northern South America. We established 8 transects of 20 m longitude along the border with 1m2 plots sampled every 4 m. SOC pre-disturbance was on average 1.794 (±SE 0.043) and the minimum value found (1.08%) was registered 6 months after the burning. Our results show that both the influence of the distance to the edge and the time of burning affect negatively the SOC and also there is a significant interaction between both variables. Our results provide improved estimates of the effect of fire on soil carbon stocks and its highly dynamic nature. We believe these finding will be a step to help better estimate GHG in this type of heterogeneous landscapes. Further it provides a tool for understanding C dynamics under a climate change context with predicted increased fire frequency, extent and severity. | Soils are one of the largest terrestrial pools of carbon, yet there is still little understanding of spatial variability for ecosystems in the tropics. Fire plays an important role in neotropical savannas ecosystems and significantly contribute to global greenhouse gas (GHG) fluxes. Nevertheless the impacts of burning on soil carbon is still uncertain in Latin America. We compared soil organic carbon (SOC) in the first 20 cm depth in savannas in pre and post fire conditions along a forests-savanna edge typically present in these landscapes of the northern South America. We established 8 transects of 20 m longitude along the border with 1m2 plots sampled every 4 m. SOC pre-disturbance was on average 1.794 (±SE 0,043) and the minimum value found (1.08%) was registered 6 months after the burning. Our results show that both the influence of the distance to the edge and the time of burning affect negatively the SOC and also there is a significant interaction between both variables. Our results provide improved estimates of the effect of fire on soil carbon stocks and its highly dynamic nature . We believe these finding will be a step to help better estimate GHG in this type of heterogeneous landscapes. Further it provides a tool for understanding C dynamics under a climate change context with predicted increased fire frequency, extent and severity.