Solute transport parameters can be determined in miscible displacement experiments, usually performed in columns with disturbed (sieved) soil samples. Experiments with undisturbed samples are uncommon, due to the difficulty of taking undisturbed samples at the size required for these experiments. Structural alteration of the disturbed material implies modifications in the pore geometry that determines hydraulic properties, including hydraulic conductivity and retention and properties related to miscible displacement. An existing model for prediction of breakthrough curves based on retention properties was tested using material from a medium-textured Ferralsol, and alterations caused by sample disturbance were investigated. Soil water retention curves and miscible displacement parameters were determined in breakthrough experiments with nitrate salts in columns filled with undisturbed and disturbed soil samples. Data obtained from the undisturbed samples showed a higher dispersion, suggesting homogenization of pore geometry and a reduction in the representative elementary volume by the disaggregation and sieving of the soil material. The transport parameters for nitrate determined in disturbed and undisturbed samples were significantly different and the model was able to simulate the observed breakthrough curves after fitting the pore connectivity parameter.

ABSTRACT:Nitrate is the main form of nitrogen associated with water contamination; the high mobility of this species in soil justifies the concern regarding nitrogen management in agricultural soils. Therefore, the objective of this research was to assess the effect of companion cation on nitrate displacement, by analyzing nitrate transport parameters through Breakthrough Curves (BTCs) and their settings made by numerical model (STANMOD). The experiment was carried out in the Soil and Water Quality Laboratory of the Department of Biosystems Engineering, "Luiz de Queiroz" College of Agriculture in Piracicaba (SP), Brazil. It was performed using saturated soil columns in steady-state flow condition, in which two different sources of inorganic nitrate Ca(NO 3 ) 2 and NH 4 NO 3 were applied at a concentration of 50 mg L -1 NO 3 -. Each column was filled with either a Red-Yellow Oxisol (S1) or an Alfisol (S2). Results are indicative that the companion ion had no effect on nitrate displacement. However, nitrate transport was influenced by soil texture, particle aggregation, solution speed in soil and organic matter presence. Nitrate mobility was higher in the Alfisol (S2). KEYWORDS: breakthrough curves, solute dynamics, leaching EFEITO DO ÍON ACOMPANHANTE NO DESLOCAMENTO DO ÍON NITRATO MEDIANTE ANÁLISE DOS PARÂMETROS DE TRANSPORTE1 RESUMO: O nitrato é a principal forma de nitrogênio associada à contaminação ambiental, e sua elevada mobilidade no solo justifica a preocupação em relação ao manejo da adubação nitrogenada em solos agrícolas tropicais. Portanto, objetivou-se com este trabalho verificar o efeito do íon acompanhante no deslocamento do íon nitrato, mediante a análise dos parâmetros de transporte do nitrato, por meio da elaboração de Breakthrough Curves (BTC) e seus respectivos ajustes pelo modelo de ajuste numérico STANMOD. O experimento foi conduzido no

The determination of the hydraulic and hydrodispersive properties of soil is necessary for the understanding of water dynamics and soil solute transport, and they are used as input data in several models. Determinations of soil hydraulic and hydrodispersive parameters are usually obtained by separate methodologies. Axisymmetric infiltration tests using a single ring infiltrometer with a conservative tracer (KBr) in the field (Beerkan-Solute) lead to the determination of the most realistic hydraulic and hydrodispersive properties of the study area. The objective of this work was the hydrodynamic and hydrodispersive characterization of an irrigated soil, classified as Fluvic Cambisol, from the lowland areas of the northeastern semi-arid region, located in the backwoods of the state of Pernambuco, in the municipality of Serra Talhada-PE. The hydrodispersive parameters were determined with the CXTFIT 2.0 program, using the CDE and MIM models. The studied soil presented hydrodynamic characteristics with high values of sorptivity (S) that were associated with high values of saturated hydraulic conductivity (Ks), indicating that the soil has good permeability and resistance to surface crumbling caused by rain drops or soil management. It was observed the predominance of the convective process, being the CDE model the one that presented the best performance in the transport of the KBr tracer under field conditions, indicating the absence of two water regions mobile and immobile in the studied soil.

Previatello da Silva (in memorian); À minha família, em especial à minha avó Gilda Borim, e aos meus amigos, pela compreensão da distância e da ausência.

resUmo: Óleos essenciais constituem um dos mais importantes grupos de matérias-primas para a indústria de alimentos, farmacêutica, perfumaria e afins, sendo o rendimento na extração especialmente influenciado por parâmetros edafoclimáticos e fatores agronômicos. Este trabalho teve como objetivo verificar se o horário de colheita do Ocimum basilicum L. (Lamiaceae) tem influência sobre o rendimento da produção do óleo essencial nas diferentes partes da planta. O experimento foi conduzido em casa de vegetação na Escola Superior de Agricultura "Luiz de Queiroz", situada no município de Piracicaba (SP). O delineamento experimental foi inteiramente aleatorizado, contendo as quatro partes da planta de ambos os horários de colheita, com um fatorial 4x2, com três repetições, sendo quatro partes das plantas (folhas, caule herbáceo, caule sublenhoso e inflorescências) e dois horários de colheita: 9h00 e 15h00. O óleo essencial foi extraído por hidrodestilação em aparelho tipo Clevenger modificado por uma hora e trinta minutos. Os resultados obtidos demonstram que o horário de colheita influenciou na extração de óleo essencial e as partes da planta de Ocimum basilicum L. que apresentaram o maior teor de óleo essencial foram a inflorescência e as folhas. pAlAVrAs-chAVe: