Seasonal variability and effect of tractor passes on soil compaction, field-saturated hydraulic conductivity, runoff and soil erosion in tilled and grassed vineyards

The hydrological response of a vineyard is influenced, among others, by the soil management that is adopted in the inter-rows. Inter-row management with tillage is known to favour runoff and soil erosion. On the other hand, the adoption of grass cover in the inter-row reduces these soil threats. Vehicles traffic in vineyards occurs along fixed paths, and has a relevant effect on soil compaction, on soil hydraulic properties, and, consequently, on runoff at the field scale. From autumn 2012 to autumn 2017 the values of field-saturated hydraulic conductivity were measured in two adjacent sloping vineyard plots in the Alto Monferrato vine-growing area (Piedmont, NW Italy) by means of the simplified falling head technique (SFH) infiltration tests that were carried out in different positions, affected or not by the vehicles passages. The inter-rows of the two plots were managed with conventional tillage and grass cover, respectively. Rainfall, runoff and soil erosion have been monitored during the observation period. Finally, soil bulk density measurements were conducted in order to evaluate the impact of the increasing number of vehicles passes on soil compaction and on field-saturated hydraulic conductivity during the whole year. The tillage temporarily increased the field-saturated hydraulic conductivity compared to the plot with permanent grass cover. A decrease in field-saturated hydraulic conductivity was observed as a consequence of cumulative precipitation and vehicles passages after the tillage. A significant increase of soil bulk density was measured in the topsoil, track position while the field-saturated hydraulic conductivity decreased from more than 1000 to 1 mm h-1. Both the Kfs, the runoff and the soil erosion varied considerably in the period of observation. In the grassed plot, the bulk density increased significantly in dry summers in the most surficial layer (0-15 cm of depth). The field-saturated hydraulic conductivity in the grassed plot were higher because of the presence of cracks. The results of the study highlighted the very short period of effectiveness of tillage in enhancing water infiltration in trafficked vineyards, and the immediate effect of vehicle traffic in increasing soil compaction.