Sampling and laboratory methods
Soil samples from 10 profiles and 12 superficial horizons were
collected. The sampling locations were selected from different
geomorphological sites and vineyard types. Given that the majority of
the active vine roots are located at a depth of 20–80 cm, the samples
were taken from the Ap and Bt or Bw horizons. Leaf samples were
collected along with the soil on which the plants were growing. The
samples were air-dried naturally and sieved through a 2-mm sieve to
remove the coarse fraction. The remaining fine-earth fraction was
homogenized before chemical analysis was carried out. The contents of
major and trace elements (Na, Mg, Al, Si, P, S, K, Ca, Fe, Mn, Ti, Ba,
Sr, V, Cr, Ce, Rb, Ni, Zn, Nd, Pb, Nb, Co, Cs, Ga, La, Y, Zr, Sc, Th, U,
Sn, Cu, As, Mo, Ta, Hf and W) in the soil and leaf samples were
determined by X-ray fluorescence spectroscopy (XRF) using a Philips PW
2404 spectrophotometer with a maximum power of 4 kW (set of crystal
analysers for LiF220, LiF200, Ge, PET and PX1, flow detector and twinkle
detector). This analytical technique has been validated for solid
matrices such as sediment (Stosnach and Mages 2009; Pessanha et al.
2010). Quality control was ensured by duplicate analysis of certified
reference samples (BCR 62, SMR 1573A, SMR 1515).