The trial was conducted for three consecutive years, in a
commercial orchard of mature orange trees (Citrus sinensis
L. Osb. cv. Navelina) grafted onto Carrizo citrange (C.
sinensis L. Osb. × Poncirus trifoliata Raf.), located in the
Guadalquivir river basin, SW Spain (37°44′4.59″ N; 5°12′
35.24″ W). The trees were planted 10 years prior to the
study, spaced at 6×5 m and drip-irrigated by two pipe lines
with pressure-compensating emitters. The average tree
height was 3 m, with a canopy diameter of 4 m. The
orchard was planted on ridges of 0.3 m high, with a NW-SE
spatial orientation. The shaded soil surface area and wet
drip zone were 30% and 17%, respectively, of the total. The
soil at the experimental site is a typical Fluvisol (FAO
1998), with sandy clay loam texture (350 gkg−1 sand;
400 gkg−1 silt; 250 gkg−1 clay) and organic matter content
below to 15 gkg−1
. It is 1.5 m deep, with a field capacity
and wilting point of 235 and 100 mm m−1 and with plant
roots growing predominantly within 0.6 m from the surface