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The background soil criteria were developed from an Ontario-wide sampling program at rural and urban parks unaffected by local point sources of pollution . Plant pigment ( Chlorophyll and HPLC ) samples can be obtained from the same sampling depths as nutrients plus at the chlorophyll maximum as determined by the profiling fluorometer . The field effort then forms a series of hunting forays where collecting is guided by the progressive enroute discovery of plant associations , and by a rhythmic sampling to capture the decay of spatial autocorrelation . Every day that passes reduces the value of the environmental sampling effort . Both computer simulations and practical trials have shown that this adaptive sampling scheme can converge from no initial knowledge to a reliable map of how soil varies .