Delineating the significance of sharp boundaries between horizons and their synergetic linkage in calcareous vineyard soils

Abstract

The present work was undertaken to appraise and delineate the significance of sharp boundaries between horizons in calcareous vineyard soils by evaluating parent material uniformity and pedogenesis. To do so, 10 soil profiles (selected from 275) were investigated. The profiles up to a depth of approximately 150 cm were opened. Macromorphological features were described following FAO guidelines. Physico-chemical properties were analysed by the usual methods. X-ray fluorescence (XRF) was used to determine elemental Ti and Zn concentrations. In terms of the main morphological characteristics, soils are reddish, and have a well-developed solum, a subangular or prismatic structure and friable moist consistency (B horizon) unlike the C horizon, which generally varies from friable to hard or very hard in a massive structure. These latter are usually related to the pedogenesis of evolved soils containing accumulations of calcium carbonate to form calcic or petrocalcic horizons. Other genetic horizons of the studied soils are argillic or cambic, which all lie directly on parent materials, in addition to a surface Ap anthropic horizon. Although the considered soils displayed a significant sharp boundary between some horizons, and even though some soil parent materials were stratified in nature and apparently formed of multidepositional regimes, certainly the vertical distribution of Ti/Zr displayed minor variations with no clear inflection with depth. Therefore, the parent materials of the investigated soils are apparently formed of homogeneous depositional materials. The morphological contrast within a profile is due mainly to pedological processes (they are very mature) rather than to geogenic ones. Nevertheless, the marked contrasts between horizons cannot be explained only by pedogenetic processes, but by other secondary processes related to agricultural use (mechanical impact of tillage). This means a partly artificial distinction that entails surface erosion and, consequently, a manifest redistribution fundamentally on surface horizons. Based on all this, it can be deduced that these soils are formed from local and not from extraregional materials.