How Well Does Zone Sampling Based On Soil Electrical Conductivity Maps Represent Soil Variability.

A study was conducted determined if EC_a-directed zone sampling  could  predict soil texture and soil organic matter patterns of samples taken by a more intensive grid sample method.  Each field was divided into three EC_a zones and soil texture and organic matter content in the top 30 cm of soil were measured.  There was a significant difference in the soil texture and SOM in both fields between EC_a Zone 1 and Zone 3.  Logistic regression showed that in both fields, approximately 80% of the grid sample sites in EC_a Zone 1 were correctly predicted.  Only 50% of the grid sample sites in EC_a Zone 3 were correctly predicted as Zone 3 in one field whereas 77% of the grid sites in EC_a Zone 3 were correctly predicted in the other field.  However, approximately 80% of the samples in the grid sites ≥ 10 m from the zone boundaries were classified correctly as compared to the samples that were <10 m from the boundary in which only 50-54% were classified correctly .  These results support the utilization of EC_a-directed zone sampling as an alternative to grid soil sampling if the transition zones are avoided.