Water table level effect on the water balance and yield of two pear rootstock

The trial was carried out in the years 1994-2002 in the Po Valley (Northern Italy); only the productive period 98-02 was considered. The orchard, cv Conference grafted on Quince-C and self rooted and Williams self rooted, was planted on an experimental field with a slope of 1.6% and an artificial water table (WT), which was maintained at a depth of 90 cm and 250 cm respectively in the bottom and upper parts of the field. The aim of the trial was to define the effect of the water table on pear tree growth and yield and to estimate the potential contribution of the capillary rising from the water table to the water balance. Fruit quality was not correlated with water table depth; nor was the trunk circumference, canopy volume or weight of pruning wood. The growth ratio of the canopy started to decrease starting from 190 cm WT for Conference/Quince-C, 240 cm WT for Conference self rooted, while no effect was observed on Williams self rooted. The marketable yield showed a strong negative correlation with shallow and deep water tables. The curve inflexion point corresponds to a water table depth of 155 cm. In general the yield decreased faster with decreases in WT (water excess) than with WT increases, even though the yield reduction caused by water deficiency resulted higher. Conference/Quince-C showed a yield reduction of 20% compared to the maximum observed yield in the case of water excess and 72% in the case of deficiency. The reduction was respectively 16% and 40% for Conference self-rooted and not relevant for Williams self-rooted. The water table contribution to the water balance was often more than the daily ETc with WT less than 120 cm; the WT contribution decreased rapidly at depths exceeding 150-160 cm.