The temporal stability of the variability in apparent soil electrical conductivity

Abstract

Apparent soil electrical conductivity (EC_a) measurements can be used for crop management in precision agriculture. However, EC_a is a soil attribute that presents spatial and temporal variability. It is affected by a group of factors that act simultaneously on the soil, such as the soil texture, moisture content, organic matter content and ionic concentrations in the soil solution, which complicates analysis. For soil and crop management, it is important to determine whether the pattern of the EC_a spatial variability changes over time. Thus, EC_a measurements have the potential for delimiting management zones that are stable over time. The objective of this work was to determine whether the spatial variability pattern of EC_a is maintained over time and under different soil conditions. To this end, the EC_a was measured at different soil depths using a portable sensor on two crop fields. The first step was to measure and generate an EC_a map for each area. By defining a path with the maximum EC_a variability, 50 sampling points were located on each field. The EC_a values were measured on 20 different dates in the 0 - 20 cm, 0 - 40 cm and 0 - 60 cm soil layers. The soil water content was measured at the same points in the 0 - 20 cm layer on the same dates. The temporal stability of the EC_a was analyzed using spatial and temporal variability maps, a correlation analysis and a coefficient of variation over time for each field. In both areas, the EC_a exhibited temporal stability in the spatial pattern variability at the three evaluated depths, even though the soil water content values changed on each date. EC_a determination presents an important alternative for mapping agricultural fields for crop management in precision agricultural systems.