Soil water balance in rainfed vineyards of the Penedès region (Northeastern Spain) affected by rainfall characteristics and land levelling: influence on grape yield

Rainfed agriculture has experienced important transformations in the Mediterranean area over the last decades. This is particularly true for traditional vineyards which have been restructured after levelling operations designed to facilitate the use of machinery. Levelling operations change soil properties and structure, negatively affecting soil hydrological processes, decreasing soil water intake and storage in the soil profile. This effect may become exacerbated under a climate change scenario as a result of increased water losses due to runoff after high intensity events and the resulting decrease in water availability for crops. This paper examines the effects of land levelling, carried out before the establishment of new vineyards, on soil water availability for vineyards in a Mediterranean climate area. These effects have been analysed taking into account the different rainfall distribution patterns in the study area, including extreme events. Soil moisture was analysed at depths of from 0 to 80 cm, for a 12 year period, in areas with different degrees of disturbance as a result of land levelling operations. Simulated rainfall was applied at the same points to evaluate the steady infiltration rate and to estimate runoff rates. Precipitation, runoff, crop evapotranspiration and changes in soil moisture were assessed for each crop stage and year for the vine varieties Macabeo, Chardonnay and Parellada. Precipitation was not enough to satisfy crop water requirements in many years, particularly during the bloom–veraison and ripening stages. Soil water content had a significant effect on grape yield, particularly the available water content during the budburst–bloom and bloom–veraison stages. Differences in yield of about 50% between years and of over 28% between levelled and non-levelled areas under similar management practices were observed.