SPATIAL DEPENDENCE OF GEOCHEMICAL ELEMENTS IN A SEMIARID AGRICULTURAL FIELD .1. SCALE PROPERTIES

Information on the spatial structure of soil chemical elements in field soils is needed to evaluate potential environmental hazards. Basic spatial properties of total soil contents of 20 major and trace elements were investigated for three different scales in a soil in northern Tunisia. In total, 314 soil samples were taken on two adjacent 40 by 40 m(2) plots (one plot sludge-amended and one without sludge). Theoretical lognormal probability distributions best fit the empirical distributions for most of the elements. Assuming complete randomness, a relative error margin of 10%, and a probability level of 0.05, average values for the sampled scales can be estimated with a minimum number of samples, which are 25 for Cd and Cr, 10 for Al, Be, Ca, Fe, Mg, and Pb, and five for other elements. The elements Al, Ca, and Fe can be sampled irrespective of scale and location (sludge vs. no sludge) with a resulting similar variance. Elements like Cd, Cr, Mg, Na, Ni, Sr, and V have a variance independent of location but are dependent on scale. Other elements, Ba, Be, Co, Cu, K, Mn, P, Pb, S, and Zn, have a variance that depends on both scale and location.