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).