Application of factorial kriging for mapping soil variation at field scale

Use of precision farming technologies requires better understanding of soil variability in physical, hydraulic and chemical properties. Some of that variation is natural, some is the result of the management history of the field. So, to match agricultural inputs and practices to site-specific conditions, the factorial kriging algorithm (FKA) was used to analyze spatial variability in some soil physical, hydraulic and chemical properties (sand and silt concentrations, water contents corresponding to potentials of -10, -50, 100, -200, -1000 and -1500 kPa and organic C concentration), measured at two depths within a single field in north Italy. A linear model of coregionalization, including, (1) a nugget effect; (2) an exponential structure with an effective range of 120 m and (3) an exponential structure with an effective range of 350 m, was fitted to the experimental direct and cross-variograms of the properties of top layer. Cokriged regionalized factors, related to short and long-range variation, were then mapped to characterize soil variation across the field. Short-range soil variation was produced essentially by differences in soil texture, whereas long-range variation in organic carbon concentration resulted in dishomogeneity of soil water retention. Quite probably, the variation in organic carbon concentration was caused by the patchy discharge of liquid manure made on the field. FKA, combining pedological expert knowledge with geostatistical techniques, could be very useful to farmers so that each area within a field is managed appropriately.