Impact of land levelling on soil moisture and runoff variability in vineyards under different rainfall distributions in a Mediterranean climate and its influence on crop productivity

This paper deals with the effects of land levelling on soil hydrological properties and spatial variability of soil moisture at different depths in bare vineyard fields under different rainfall distributions over the year. The research was carried out in a levelled vineyard in the Penedes region (NE Spain), which is representative of the land management practices in that area. Twelve locations were instrumented in the selected plot to control soil moisture periodically at different depths (0-20, 20-40, 40-60 cm, using a TDR tube probe), and runoff (using Gerlach collectors located at the same positions) during the period April 2002-March 2004. Rainfalls were recorded at one-minute intervals in the experimental field using a pluviometer linked to a data-logger. The vine yield and its relationship with the rainfall distribution over the year was evaluated in this levelled vineyard vs. a less transformed vineyard. The land levelling works carried out in the plot before the establishment of the vineyard led to major differences in soil depth (ranging from 50 to 110 cm) and in soil layer characteristics along and across the plot. This helps to generate different soil moisture conditions at the same depth at different positions of the plot. The areas located at the top of the plot showed soil moisture conditions in the surface layer that were up to 5% lower than down slope, although with high variability across the plot. Soil moisture in the whole profile depends on the intensity of rainfall more than total rainfall. At high intensities, soil moisture increases only occur in the surface layer, but no significant increases are observed in deeper layers, where vines have most of their roots. On the other hand, under low intensity rainfalls the soil water content increases in the whole profile. Levelled plots showed a yield reduction in comparison with those undergoing less transformation, which was exacerbated by a very irregular rainfall distribution: for a similar total rainfall, but with dry periods during the stages in which the water requirement for vines is higher, grape production was up to 50% lower in areas with high land transformation, where Chardonnay was planted, and up to 16% lower at the bottom areas, where Macabeo was planted.