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.

Temporal Stability of Management Zone Patterns: Case Study with Contact and Non-Contact Soil Electrical Conductivity Sensors in Dryland Pastures

“…Numerous studies use data from sensors to map soil physical and chemical properties to divide the field into smaller, more homogeneous areas (management zones, MZs) [ 8 , 9 ]. Surveying soil spatial variability is the basis for identifying within-field areas of soil similarity, defining MZs, and supporting decision making, for example, to decide on the locations of direct soil sampling (smart soil sampling) [ 10 ] or for variable rate application (VRA) of agricultural inputs [ 1 , 2 , 11 , 12 , 13 ]. These subfield regions constitute areas that have similar permanent characteristics, such as topography and nutrient levels [ 14 ].…”

Spatial pattern consistency and repeatability of proximal soil sensor data for digital soil mapping

“…Martini et al (2017) compared repeated EMI measurements with high‐resolution soil moisture and temperature data and reported that the spatial patterns of ECa differed from those of soil water content and that the relation between both variables was changing over time. Overall, most studies indicate that the influence of moisture on the spatial patterns of ECa and the prediction ability of ECa for soil texture (in particular clay content) increases at higher levels of moisture (Calamita et al, 2015; McBratney et al, 2005; Zhu et al, 2010) and that differences in seasonal ECa patterns are likely related to differences in the moisture and texture‐dependent drying and/or rewetting behaviour of the soils (Farahani & Buchleiter, 2004; Lück et al, 2009; Martinez et al, 2010; Medeiros et al, 2016). In consequence, repeated ECa measurements have been suggested for assessing agricultural management effects (Blanchy et al, 2020) and the temporal stability of ECa for mapping hydropedological properties (Liao et al, 2014).…”

Temporal Comparisons of Apparent Electrical Conductivity: A Case Study on Clay and Loam Soils in Mississippi

“…Yet, a better understanding of the stability of EC a measurements is needed so that users of the equipment have insight into the temporal stability of the readings. Using electromagnetic induction or the Veris mobile platform [17] [18] [19] [20] reported EC a stability ranging from 2 months to 4 years. Also, more information is needed on comparing EC a maps derived from over a period of time because the information would be valuable to farmers, consultants, and researchers interested in using the equipment to make management decisions.…”