Tuesday, November 14, 2006 - 10:30 AM

Testing a Theory About Relationships Between Electrical Conductivity Data and Soil Properties.

Ruth Kerry, Brigham Young Univ, Geography Dept, 690 SWKT, Provo, UT 84602 and Elizabeth B. Gillins, Brigham Young Univ, Geography Dept, 690 SWKT, Provo, UT 84602.

Using electrical conductivity data (ECa) in soil survey is popular because it is related to several soil properties. Particular use has been made of ECa data in precision agriculture because it is related to properties that could affect crop yield. Although theoretically sound reasons exist to explain these relationships, they vary spatially, making ECa data interpretation difficult, even within fields. Also some have attempted to establish relationships with ECa for which there is no theoretical basis. McBratney et al. (2005) suggest that theoretically sound relationships developed between high frequency devices like time-domain reflectometers can be used to inform interpretation of the lower frequency ECa data. A three part theory was presented: 1)  If the soil is hyper-electrolytic. ECa measures salinity. 2)  If the profile thickness is thinner than the effective depth of measurement and the underlying material has a smaller ECa, ECa indicates soil depth. 3)  If there is no compaction and the electrolyte concentration balances with soil charge, ECa represents variations in clay and moisture content. Our aim was to determine whether this model provides insights into the causes of patterns of ECa in several fields with soil likely to meet the different conditions mentioned above. This was assessed by determining which of the conditions the data points in the fields met then moving correlation analysis was used to determine the relationship between ECa and relevant soil properties in the vicinity of each data point. Results suggest that within most fields different conditions from the model apply in different parts of the field. This shows that using the model provides some interpretative insight for ECa data. A practical method of incorporating this into soil mapping for management zone delineation will be presented.