In each experimental plot, samples were collected from each soil layer, at a depth of 0-40 cm, from the center of each plot, following a zigzag route. Soil samples were mixed to ensure homogeneity, dried at 40°C, and sieved through a 2-mm screen; microoelements and macroelements were extracted by the Mehlich 3 procedure (Mehlich and Mehlich 1984). Soil pH was measured in H2O and KCl (0.1 M). For elemental analysis (CNS), the soil samples were ground in a mortar to obtain a fine powder.

Sampling was carried out in spring and autumn. Needle samples were also collected, approximately 25% from the floor of the plot (Ballard and Carter 1986), approximately 25% from the upper third, approximately 25% from the growth of the year, and approximately 25% from the sunniest branches (Will 1985). The needle samples were dried at 60°C to constant weight and were ground for CNS analysis by inductively coupled plasma optical emission spectrometry.