The study area is located in the Pampean region of Argentina, in the northwest of Buenos Aires Province, covering about 50,000 km 2 , within an area of great plain with particular hydrologic characteristics, where vertical water movements predominate over horizontal. The objective of this work is the analysis of the relations between different hydrologic scenarios (characterized by the soil water balance and the water table levels) and the yields of soybeans that have been increasing in recent years. It is concluded that water table fluctuations are strongly related to the elements of the local hydrologic balance. On the other hand, the geographic distribution of soybean yields corresponds directly with the values of the soil water reserve during the critical stages of the growth. After dry periods, the lowering of the water table makes access to water from the root zone difficult, and the crop is susceptible to the effects of drought. However, after wetter periods the extra contribution from the water table situated near the surface is favorable for growth, often preventing its deterioration in conditions of drought. Nevertheless, an excessive rise of the water table can produce disadvantages at seedtime and during harvest. The importance of an evaluation of the different scenarios that may have significant implications for agricultural activity is discussed.

Soil water surplus and deficit occur frequently in Buenos Aires province in Argentina. This paper analyses the soil water surplus in a sub-area, the Salado River basin, in the period 1968-2008. This basin is divided in seven drainage areas, delimitated according to the National Water Resources. The series of soil water surplus data were adjusted by means of the theoretical normal cubic-root probability distribution, and the mean areal soil water surplus value of 300 mm was considered as a threshold above which floods can cause severe damage. An increase in the frequency of extreme events and in their tendency exists during the recent years, coherent with the increase of precipitation recorded in the region. The statistical significance of the results was assessed using the Mann Kendall and MAKESENS tests. The results showed a relevant temporal variability, but did not show significant tendencies.

Daily soil water balances are estimated for the period 1951-2006 in the Pampean flatlands. Daily soil water surplus is the major output with their annual trends, being analysed because of their harmful effects on crop's harvest and floods. Soil water surplus trends were analysed founding positive trends, although only two stations were statistically significant at probability level of 95%. Differing phases of ENSO -using the multivariate ENSO index (MEI) -have differing impacts on rain and soil moisture conditions. The probabilities of occurrence of predetermined soil water surplus and hence flood risk are calculated and mapped.

El objetivo del presente trabajo es el de evaluar el manejo de los cultivos de tomate primicia y de poroto seco para la exportación en Orán, mediante un balance hidrológico diario, en relación a las necesidades de riego complementario pasadas y presentes. Con los datos pluviométricos de la localidad de Orán se confeccionaron tres balances hidrológicos diarios simulando diferentes manejos del suelo: pastura natural, abono verde - cultivo de tomate y abono verde - cultivo de poroto. Posteriormente se analizó la serie obtenida de almacenajes de agua edáfica y se calculó la probabilidad de sequía absoluta, sequía condicional y humedad óptima para cada década del año. Por último, se estudió para el período crítico y para todo el ciclo del cultivo, la posibilidad de aplicación de riego complementario. El seguimiento de los almacenajes medios simulados mostró que la frecuencia de sequías, para justificar la aplicación de riego, fue mayor a mediados que a principios del presente siglo, cosa que no sucede desde las últimas décadas, debido al incremento que han sufrido las precipitaciones pluviales.