Soil and management effects on aggregation and organic matter dynamics in vineyards

Abstract

Vineyards in hilly areas are often prone to erosion because of poor soil development, low soil organic matter (SOM) contents, and severe slopes. Permanent grassing, besides providing protection against erosion, can foster the soil resistance to degradation by increasing SOM that, in turn, favours the formation and limits the turnover of stable aggregates by promoting interactions between SOM and soil minerals. Although a soil’s capacity to physically protect SOM is known to depend on management practices, soil properties may interact causing the soil response to vary even at relatively low spatial scales, thereby warranting site-specific sustainable soil management. The objective of this study was to evaluate how differences in soil properties within the same vineyard may modulate the effects of management practices on aggregate formation, stability as well as SOM dynamics. We exploited the spatial differences in soil types and properties in an experimental vineyard by sampling topsoil samples (0–5 cm) with contrasting texture and pH to include a non-calcareous clay loam from an Alfisol (pH 6.8, 18.6 g kg−1 organic C, 28% clay) and a calcareous loam from an Entisol (pH 8.0, 14.8 g kg−1 organic C, 14% clay), both managed for 3 years under permanent grass vs. autumn tillage. Four aggregate size fractions were separated by dry sieving, and characterized for their organic C content and distribution between functional pools by density fractionation, and their resistance to breakdown and organic C loss during wet sieving.Soil type affected aggregate formation and stability with a greater abundance of larger aggregates richer in SOM in the clay loam with respect to the calcareous loam. Tillage enhanced aggregate breakdown and SOM loss, but the effects were highly dependent on the intrinsic soil properties that drive the different mechanisms of aggregate formation and stabilization. The largest macroaggregates were most susceptible to disruption and organic C release by tillage, but a soil-dependent effect was observed as those in the calcareous Entisol were more vulnerable than those in the Alfisol topsoil, particularly due to rapid losses resulting from slaking, swelling and dispersion. Although the aggregates in fine-textured topsoil may be relatively less vulnerable to tillage, the higher proportion of organic C in the larger macroaggregates may make them nonetheless prone to significant organic C loss (in the form of POM (particulate OM) or SOM-rich fine aggregates) unless appropriate management is adopted. Therefore, special attention should be given to the spatial variability in soil properties when planning vineyard management to reduce soil degradation.