Arrouays, D.;Marchant, B. P.;Saby, N. P. A.;Meersmans, J.;Orton, T. G.;Martin, M. P.;Bellamy, P. H.;Lark, R. M.;Kibblewhite, M.

INRA, US 1106, InfoSol Unit, CS 40001 Ardon, F-45075 Orleans cedex 2 (France);Cranfield University, Cranfield, Bedfordshire, MK43 OAL (UK);Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ (UK)

networks;sampling;soil quality;spatial analysis;temporal analysis

Numerous scientific challenges arise when designing a soil monitoring network (SMN), especially when assessing large areas and several properties that are driven by numerous controlling factors of various origins and scales. Different broad approaches to the establishment of SMNs are distinguished. It is essential to establish an adequate sampling protocol that can be applied rigorously at each sampling location and time. We make recommendations regarding the within-site sampling of soil. Different statistical methods should be associated with the different types of sampling design. We review new statistical methods that account for different sources of uncertainty. Except for those parameters for which a consensus exists, the question of testing method harmonisation remains a very difficult issue. The establishment of benchmark sites devoted to harmonisation and inter-calibration is advocated as a technical solution. However, to our present knowledge, no study has addressed crucial scientific issues such as how many calibration sites are necessary and how to locate them.