Meteorological conditions.
A meteorological station (Mod. Multirecorder 2.40; EGT, Florence, Italy) sited within 250 m of the experimental field was used to measure global radiation and photoperiod data from October to April. Data were recorded every hour. Global radiation fell from October to February (6.8 MJ m−2 in the first decade of February) and then rose up to 23.3 MJ m−2 in the third decade of April (Fig. 1). Similarly, the hours of radiation decreased in November and December (up to 10 h in the latter month) and increased from January up to 14 h in the first decade of April. Mean air temperatures and rainfall were found to comply with the 30-years weather conditions of the zone.