MOSSO_SoilChemistry_HistoricalSites_Annual_2008-2020

Each soil sample consists of three subsamples that are homogenised by sieving at 2 mm. An aliquot of 20 g of fresh soil is extracted with 100 mL K2SO4 0.5 M, while 10 g are fumigated using chloroform for 18 h before extraction with 50 mL K2SO4 0.5 M. The concentration of DOC in not fumigated soil extracts (extractable DOC) is determined with a TOC analyzer (Elementar, Vario TOC, Hanau, Germany) after filtration with 0.45 μm nylon membrane filters. The microbial carbon (Cmicr) is estimated as the difference in extractable DOC between fumigated and non-fumigated samples, corrected using a recovery factor of 0.45 (Brookes et al. 1985, https://doi.org/10.1016/0038-0717(85)90144-0). Extractable N-NH4 concentration in soil extracts is measured spectrophotometrically (U-2000, Hitachi, Tokyo, Japan) using a modified Berthelot method based on the reaction with salicylate in the presence of alkaline sodium dichloroisocyanurate (Crooke and Simpson 1971, https://doi.org/10.1002/jsfa.2740220104). Extractable N-NO3 concentration in soil extracts is measured spectrophotometrically (U-2000, Hitachi, Tokyo, Japan) using the Greiss reaction (Mulvaney 1996, ISBN-10: ‎ 0891188258; ISBN-13: ‎ 978-0891188254) modified according to Cucu et al. (2014, https://doi.org/10.1007/s00374-013-0893-4). Extractable TDN is measured as reported for DOC. Extractable DON is determined as the difference between extractable TDN and inorganic nitrogen (extractable N-NH4 + N-NO3) in the extracts. Nmicr is estimated from the difference in extractable TDN between fumigated and non-fumigated samples corrected using a recovery factor of 0.54 (Brookes et al. 1985, https://doi.org/10.1016/0038-0717(85)90144-0).