On the Description of Soil Variability Through EMI Sensors and Traditional Soil Surveys in Precision Agriculture

In Precision Agriculture electromagnetic induction (EMI) sensors are generally used to obtain soil electrical conductivity (EC) maps for the delineation of homogeneous management zones (MZ). EC measurements are related to many physical-chemical soil properties and, moreover, are average values referred to the soil depth explored by the sensor. Consequently, the following questions arise: how reliable are EC measurements to describe soil variability, compared to the data provided by a pedological survey? To which extent MZs correspond to pedological units in a soil map? Texture analysis was conducted on 38 soils samples collected at three depths with a manual auger in a rice farm (province of Pavia, Italy) characterized by sandy-loamy soils. Four pedological units were recognized, mainly based on differences in clay content distribution with depth. Four MZs were recognized from the EC maps. MZ and pedological soil maps showed similar spatial distributions of soil types, particularly at field scale. However, at the farm scale, different MZs may correspond to the same pedological unit, because of the different soil properties to which the two classification approaches are sensitive: clay contents for pedological soil mapping, and sand contents for MZ mapping. Finally, ANOVA was carried out to evaluate the statistical significance of this result.