Spatial Variability Analysis of the Effective Depth to Petrocalcic Horizon Using Electrical Resistivity in the Southern Pampas of Argentina.

Soil development in the plain landscape of the southeastern Buenos Aires Province is underlain by a discontinuous petrocalcic horizon, locally termed tosca. Depth to root restricting layer affects both soil moisture and nutrient availability, resources strongly correlated to crop production. Efficient methods for accurately measuring are necessary to determine spatial variability of effective depth (ED) from a perspective of precision agriculture. Apparent electrical conductivity (ECa) measurements were conducted at 0-30 cm and 0-90 cm depth with a 3100 Veris soil electrical resistivity sensor, in a 32 hectares field. Effective Depth was determined with a Giddings Soil Sampling equipment in a 30x30 m grid. The study site is situated within two soil series: Tres Arroyos (Petrocalcic Paleudoll) and Semillero Buck (Typical Argiudoll) in the Cartographic Unit (CU) TA48. Three zones of ECa were delimited (ZECa) and three composite samples from each zone were obtained. Gravimetric water content, clay content (As), pH and cation exchange capacity (CEC) were analyzed. ECa 0-30 cm showed positively strong correlation with ED (r=0.82). Shallow soil depth (<50 cm) exhibited similar As, CIC and pH. High ZECa could be spatially related with shallow soils identified within Tres Arroyos series. Middle and Low ZCEa could be associated with deeper soils related with Semillero Buck series. The ECa measurements were particularly well suited for establishing within-field spatial variability of ED and contribute to study inherent soil properties. Although tosca layer has a great variability in depth, structure and CaCO₃ content, the spatial measurements of ECa could be used as an indicator of soil properties.