SPACE-TIME ANALYSIS OF WATER STATUS IN A VOLCANIC VESUVIAN SOIL

Many studies have shown that the observations of soil hydraulic properties should not be considered purely random, given that they possess a structure which may be described by means of stochastic processes. The techniques used for analyzing such a structure have essentially been based either on the theory of regionalized variables or, to a lesser extent, on the analysis of historical series. This work attempts to combine the two approaches mentioned above by means of a study of parameters h and theta, which characterize soil water status, in the space-time domain. The data of the analyses were recorded in the open field during a controlled drainage process, evaporation being prevented, along a 50 m transect in a volcanic Vesuvian soil. The statistical models used may be traced back to a generalization of the classical ARMA models, commonly used in time series analyses, so as to take the following into account; (a) spatial anisotropy in the phenomena studied; (b) simultaneous physical relations between h and theta; (c) space-time interrelations which characterize these parameters. In particular, in the work h and theta are shown to present: (i) marked non-stationarity on mean attributable to the time dimension; (ii) a strong non-stationarity in variance only for parameter h and in the time dimension; (iii) a different space-time structure which cannot be influenced by possible crops; (iv) strong anisotropy just for the space dimension; (v) simultaneous linear relations confined to lesser time values.