The water yield component of the SWRRB model was validated in a watershed of 125 ha, permanent stream flow, 35 percentage of steep gradient, sandy loam soils, seasonal rainfall and grassland vegetation, in Macapo, Cojedes State, Venezuela. Water yield was measured with a Stevens water level recorder installed in a gauge channel, and compared to the predicted water yield by the model. Using directs inputs, the model underestimated water yield (with relative differences between -100 and +800 percentage). In almost all cases, as well as rainy days, surface runoff was ignored. Base flow was ignored by the model. Subsurface runoff was the more important flow in terms of model perfomance. Flows behavior can be caused by the underestimation of the CN at the high values of retention constants. Using indirect inputs, it was obtained a higher, but more variable, water yield. Water yield was found very sensitive to Curve Number, Saturated Hydraulic Conductivity and Available Water Content, this shows the involved risk in the application of the model when estimated inputs are used. SWRRB must not be used for detailed planning and design in small watershed, but it may be useful to evaluate watershed degradation and response trends in terms of land use and management changes.

In order to study the dynamics of physicochemicals components of water obtained from lagoons situated on physiographys of “bancos, bajíos y esteros” that serve as watering places for cattle, samples from savannas of Mantecal, Apure state, Venezuela were taken and measured between march - 2005 to april - 2007. Results showed proverty of mineral elements for adecuate mineral nutrition, low electric conductivity and slightly acids pH, which in periods of draught had a tendency to neutrality. Sodium, potassium, calcium cations and less frequent magnesium, presented greater values on the lagoons in the physiographys of “esteros and bajíos” specially during the dry season. Concentrations of sulfur and iron rise during the dry season, coinciding with reproductive season, this could induce metabolic disorder related to mineral nutrition of the herds | Con el fin de estudiar la dinámica de los componentes físico-químicos de las aguas de lagunas de abrevaderos ubicadas en fisiografías de bancos, bajíos y esteros de una sabana hiperestacional de Mantecal, estado Apure, Venezuela se realizaron durante el período marzo - 2005 a abril - 2007 evaluaciones a muestras obtenidas de las mismas. Se encontró en general una pobreza de elementos minerales para una adecuada nutrición mineral, la existencia de bajas conductividades eléctricas y pH ligeramente ácidos, aún cuando en períodos de sequía tienden a la neutralidad, disminuyendo con el inicio de lluvias. Los cationes sodio, potasio, calcio y en menor frecuencia el magnesio, presentaron mayores valores en lagunas ubicadas en las fisiografías de esteros y bajíos, especialmente durante los períodos de sequía. Mientras que las concentraciones de azufre e hierro se elevaron en período de sequía, cuando ocurre la temporada de apareamiento, lo cual podría inducir desordenes metabólicos en la nutrición mineral de los rebaños

Con el fin de estudiar la dinámica de los componentes físico-químicos de las aguas de lagunas de abrevaderos ubicadas en fisiografías de bancos, bajíos y esteros de una sabana hiperestacional de Mantecal, estado Apure, Venezuela se realizaron durante el período marzo - 2005 a abril - 2007 evaluaciones a muestras obtenidas de las mismas. Se encontró en general una pobreza de elementos minerales para una adecuada nutrición mineral, la existencia de bajas conductividades eléctricas y pH ligeramente ácidos, aún cuando en períodos de sequía tienden a la neutralidad, disminuyendo con el inicio de lluvias. Los cationes sodio, potasio, calcio y en menor frecuencia el magnesio, presentaron mayores valores en lagunas ubicadas en las fisiografías de esteros y bajíos, especialmente durante los períodos de sequía. Mientras que las concentraciones de azufre e hierro se elevaron en período de sequía, cuando ocurre la temporada de apareamiento, lo cual podría inducir desordenes metabólicos en la nutrición mineral de los rebaños | In order to study the dynamics of physicochemicals components of water obtained from lagoons situated on physiographys of “bancos, bajíos y esteros” that serve as watering places for cattle, samples from savannas of Mantecal, Apure state, Venezuela were taken and measured between march - 2005 to april - 2007. Results showed proverty of mineral elements for adecuate mineral nutrition, low electric conductivity and slightly acids pH, which in periods of draught had a tendency to neutrality. Sodium, potassium, calcium cations and less frequent magnesium, presented greater values on the lagoons in the physiographys of “esteros and bajíos” specially during the dry season. Concentrations of sulfur and iron rise during the dry season, coinciding with reproductive season, this could induce metabolic disorder related to mineral nutrition of the herds