2. Materialsandmethods
2.1. Orcharddescription
The research was realized in a farm located in the Eastern Sicily (Italy), where twenty years old “Tarocco” orange trees [Citrus sinensis (L.) Osbeck] grafted on sour orange rootstock [C. auran- tium (L.)] were cultivated with a planting distance of 6 m × 4 m (416 trees ha−1 ). The area is characterized by high summer and low winter temperatures. The rainfalls are concentrated in the autumn–winter season. During the experimental period total rain- fall had typical values of this Mediterranean region. The irrigation was carried out with two micro-sprinklers per plant with an aver- age annual water supply of 3360 m3 ha−1 . Soil of citrus orchard was a sandy-loamy soil, with a low content of organic matter, high con- tents of active lime and total calcium carbonate, low content of available Fe (Suppl. Ord. G.U. No. 248, 21.10.1999, Method IX.3). Main chemical–physical soil parameters are reported in Table 1 (soil sampled at 0–30 cm of depth, layer most explored by citrus roots).
Before treatments (early spring season, 2008), plant leaves showed typical symptoms of Fe deficiency by green discoloring, in particular the intervenial leaf yellowing, starting from apical leaves. Trees canopy showed symptoms of Fe chlorosis throughout the year, but they were more evident in spring, when shoot growth is faster and the bicarbonate concentration in the soil solution buffers