Spatial patterns of SOC, SON, 137Cs and soil properties as affected by CD redistribution processes in a Mediterranean cultivated field (Central Ebro Basin)

Mediterranean mountain agroecosystems are sensitive areas to soil degradation due to climatic conditions and anthropogenic pressure from agriculture and grazing practices. Soil redistribution processes affect the spatial variability of soil properties and nutrients, as soil organic carbon and nitrogen (SOC and SON) are linked to soil quality and soil functions. A representative cereal field of rain-fed agroecosystems in a Mediterranean mountain environment where conventional and conservation agricultural practices have been implemented was selected on the northern border of the Ebro valley (NE Spain) to gain a better understanding of the effect of soil redistribution processes on the spatial pattern of soil properties at field scale. One hundred and fifty-six bulk (30-50 cm) and 156 topsoil samples (5 cm) were collected on a 10 x 10 m grid. Furthermore, 21 soil samples (40 cm) were collected at a nearby undisturbed reference site. Cs-137 massic activity was measured on bulk and reference soil samples, and SOC and SON were measured on all soil samples. The characterisation of SOC pools into active (ACF) and stable carbon fraction (SCF) was carried out to study SOC pool dynamics. The fallout (CS)-C-137 was used in order to identify areas of Cs-137 loss and gain and that of soil within the study field. Similar spatial patterns and direct and significant correlations (p < 0.01) were found between Cs-137 and soil nutrients. As much as 70% of the total study field had lower values of Cs-137 inventory than the reference for the area. In addition, there was a generalised loss of soil nutrients. SOC gain was found in less than 1% of the study field and there was a large loss of SON compared to the undisturbed reference site. Higher and significant (p < 0.01) contents of soil nutrients were found in topsoil than in bulk samples. Furthermore, there was an enrichment of the relative contribution of ACF to total SOC in sampling points where there was a Cs-137 gain in both bulk and topsoil samples as a consequence of the soil redistribution particles by tillage and runoff. Understanding patterns of soil nutrients can be useful for developing or implementing land management strategies to preserve soil quality in Mediterranean agricultural areas. (C) 2015 Elsevier B.V. All rights reserved.