Spatial speciation - A new approach to assess soil analysis methods

Abstract

Geostatistical methods were used to examine the "spatial speciation" of phosphorus (P) in an agricultural cambisol, whereby in this study speciation was defined functionally, considering the strength of the bonding between phosphorus and soil particles as an indication of its plant availability as well as its mobility in the soil. P species were analyzed employing a range of methods which differed in their extraction force. Extractants used were aqua regia, nitric acid, calcium lactate, ammonium acetate and calcium chloride. Soil texture, pH, Fe, CaCO3 and total carbon concentrations were determined in air-dried soil samples. Three different P pools could be identified by geostatistical methods, whereby the P concentration of each pool displayed a different continuity depending on distance and direction. The distribution pattern of the soluble P pool appeared to be governed by the adsorption capacity of the soil and subsequently by the spatial variability of soil texture. The influence of topography on soil erosion processes was reflected in the variation of total P, whereas the labile P fraction was apparently related to recent fertilizer practices. Results of this study indicate that an evaluation of the spatial speciation of a nutrient may provide essential information about its behavior in the environment and as such should be considered when choosing soil analysis methods.