Spatial distribution of solar radiation and its effects on vine phenology and grape ripening in an alpine environment

Climate, soil and vineyard performance were characterized in the northern Italian alpine valley of Valtellina to develop an eco-physiological model for zoning the district’s viticultural aptitude. Based on a representative sample of 54 small, steep-sloped terraced vineyards planted with the late-ripening red cv. Nebbiolo, the model included three-year (1998-2000) data sets for phenology, maturity curves, yield, vigor, and grape assays, with appropriate indices to manage these sets. Soils were characterized by pedological description and climate by both annual values of potential photosynthetically active radiation (PPAR) and estimated thermal fields expressed as growing degree days (GDDs) on base 10°C; PPAR ranged from 2700 to 3200 MJ m-2year-1 and GDDs from 1100 to 1800. Vineyards showed a 12-day range in phenological timings, with early sites showing the highest technological maturity and medium sites the highest phenolic maturity. Elevation and PPAR were the main environmental factors affecting vine budbreak and bloom date; veraison was also affected by crop load and its interaction with PPAR availability. Technological maturity was affected by elevation, phenolic maturity by crop load, and PPAR and its interaction were affected by crop load and elevation. The highest phenolic maturity was recorded in low cropping vineyards at low elevation and PPAR.