Air temperatures inside the greenhouse ranged between 20 and 25 ◦C during the daytime and fell to 10 to 15 ◦C at night. The vapor pressure deficit (VPD) reached a daytime maximum of between 0.7 kPa (Day 307) and 1.2 kPa (Day 314) (Figure 1). Photosynthetically active radiation (PAR) varied from day to day,reaching a daytime peak value of between 170 µmolm−2 s−1 (Day 307) and 340 µmol m−2 s−1 (Day 314),on about 1/3 of full sunlight (Figure 1).
Four trees were irrigated once per day with nutrient solution (3.75 mmol L−1 NH4NO3, 1.3 mmol L−1 NH4PO4H2, 0.01 mmol L−1 Fe and 0.01 mmol L−1 Zn). This irrigation was supplied using a single lateral line that had two compensating drippers (qe = 2 L h−1) for each tree. The irrigation was controlled automatically by a head unit programmer which maintained
soil matric potential at about −30 kPa (monitored with
tensiometers placed at 20 cm depth). The soil water
content was estimated gravimetrically along the experiment. Beyond November 9 (Day 313), with the
soil mixture initially at field capacity (θ m=31.3%),
water was witheld for four days. Soil water content
declined steadily over this period to reach a value close
to wilting point (θ m = 15.2%) by day 317. After these
four days (Day 318 at 10.30 a.m.) pots were then
re-irrigated to their full water holding capacity.