Effect of high density and dynamic tree spacing on yield and quality of the hazelnut cultivar 'Tonda Gentile Romana'

Training systems and planting density in Lazio (central Italy) are based on bushes at a density of 400-500 plants per hectare. High-density systems have received little attention. In an adult orchard of ‘Tonda Gentile Romana’, with single-stem plants spaced 2.5 x 4 m, plant density was reduced from 1000 to 500 plants per hectare in 2000 and 2001, seventeen and eighteen years after planting. Vegetative growth, yield and nut quality were measured from 2001 to 2003, in order to quantify plant response to tree spacing in a medium-vigour cultivar. The results indicate good productivity and quality after eighteen years of high density, and the beginning of competition among plants. When the distance between plants on the line increased from 2.5 to 5 m, vegetative growth improved and the trunk cross-sectional area and canopy volume increased. Yield was affected by spacing, year and the interaction year * spacing. Yield per hectare decreased in the first year after plant removal. In the following years, yield per hectare was variable, as a consequence of difficulties in achieving an equilibrium between vegetative and productive activity, and plant production improved. Plant density had only a slight effect on nut quality, as revealed by nut traits and defects and seed chemical composition. The oil content was lower in the high-density thesis. The effect of the year on sugar and oil accumulation was evident, with higher concentrations in 2002, when the summer was cooler and rainy.