Modeling water content of a vineyard soil in the Douro Region, Portugal

The soil moisture of a vineyard soil under two different plantation systems , bench terrace and straight down the slope (German system), was measured w eekly from 1991 to 1997 in the Demarcated Region of Douro - the Port wine p roducing region in Portugal. The soils of the region are extremely stony, l ocated on steep slopes along narrow valleys. These conditions complicate th e study of soil water relations with deterministic functions. We fitted a l arge data set to stochastic models, with the objectives of (a) determining which stochastic model best forecasts soil moisture in various planting sys tems, (b) based on chosen models, objectively evaluate variation of soil mo isture in each planting system, and (c) finding an objective factor on whic h to base management decisions. Soil moisture variation was best represente d by a time frequency model (Fourier series). Soil under straight down the slope plantation had significantly higher water reserves for most of the ye ar than bench terrace plantation but the difference was not high enough to drive a significant shift on production and fundamentally affect the choice of which system to choose for new plantations. The model-generated data su ggested a superficial and subsuperficial downflow of water from upper slope s in the straight plantation relative to bench terraces. However, the model failed to shed additional information on the mechanisms related to soil wa ter balance. Data generated by the time frequency model might prove useful for other management decisions such as schedule and intensity of topping an d pesticide application.