Ea1110

Soil texture was obtained by the pipette method (Day, 1965) after the specimens were submerged in NaClO (pH 9) for 24 h to destroy the organic cements. Soil pH was measured in a suspension (solid:liquid ratio 1:2.5) by a combined glass-calomel electrode. Soil mineralogy was assessed by x-ray diffraction with a Philips PW 1830 diffractometer (Fe-filtered Co K1 radiation, 35 kV and 25 mA). A semi-quantitative estimation was obtained after identification of the minerals on the basis of their characteristic peaks. Separates of 0.5-2 mm diameter, recovered from the extraction residue of the organic matter fractionation protocol prior the 0.5 M HCl solution treatment (see below), were observed under an optical microscope. Total C and N were determined by a Carlo Erba EA1110 dry combustion analyzer. The amount of total organic C (TOC) was measured by dichromate digestion, heating the suspension at 180°C for 30 min (Allison, 1965) . As the Walkley-Black method without application of heat is considered not able to oxidize the coarse particulate organic matter, it was used to estimate the amount of the most oxidizable organic matter (e.g., Frink, 1995) , here called organic C (OC). The content of inorganic C was obtained from the difference between total C and TOC.

Samples dried at 40 0 C (about 1kg each) were ground, passed through a 2 mm sieve, and used to measure pH and total C and N content. The pH was determined potentiometrically in H2O (1:8 w/v). Total C and N were determined by dry combustion method using a CHNS analyzer (EA-1110, Carlo Erba Instruments, Milan, Italy) . Total solid content (TS) was estimated as the fraction of the dry mass after samples were dried at 105 0 C for 24 h. Organic matter (OM) was determined as the loss on ignition (Heiri et al., 2001) at 550 0 C until constant weight was obtained. Water extractable Al, Ca, Ba, Cd, Cu, Fe, Mg, Mn, Na, Ni, P, Pb, S, and Zn were determined by using 10 g of ground compost samples that were added to 100 ml of distilled water (1:10 w/v) and shaken for about 1 h at 10 rpm. The suspension was then centrifuged for 10 minutes at 300 g and the solution filtered using Whatman 42 filter. The extract was used to determine the concentration of the elements on an ICP-MS (Pröfrock and Prange, 2012) (link).