Camps Arbestain, Marta (NEIKERNEIKER, Berreaga, 1DERIO-BIZKAIA, 48160, Spain; Phone: 34944034328; Fax: 34944034310; Email: mcamps@neiker.net)

Determination of Organic Carbon Fractions of Agricultural and Forest Soils on the Basis of Their Degree of Oxidation with Permanganate

M. Camps Arbestain*, Z. Madinabeitia, I. Martinez de Arano, A.Gonzalez Arias, M. Pinto, A. Aizpurua, M.A. Ortuzar, F. Macias

The aim of the present study is to investigate the lability of soil organic carbon (SOC), measured on the basis of the ease of its oxidation with permanganate. For this, samples of the surface horizons of 44 soils under Fagus sylvatica L., 35 soils under Pinus radiata D. Don, 20 soils under Quercus ilex L., and 12 agricultural soils, all located in the Basque Country (N Spain), were analyzed. Most of the soils under Fagus sylvatica stands have developed from marlstones, sandstones, and limestones, and those under Pinus radiata stands from marlstones, sandstones and volcanic materials. On the other hand, most agricultural soils and those under Quercus ilex stands have developed from limestones. The soils were air-dried and passed through a 2-mm sieve prior to analysis. The oxidability of SOC by permanganate in the Fagus sylvatica forest soils was determined with 33 mM KMnO₄ after different incubation times (1 h, 3 h, 6 h and 24 h), and that of the rest of the soils with the same reagent after 1 h incubation. For all soils, general soil properties (SOC, total N, pH, CEC, particle-size distribution) were determined. Analysis of SOC was carried out with (i) K₂Cr₂O₇, following the Walkey-Black method, and (ii) a LECO C analyzer (corrected for carbonates when present). The Fourier transform infrared spectra of untreated soil samples were also obtained. The pH values of soils under Fagus sylvatica stands ranged between 4.0 and 8.2, those of under Pinus radiata stands between 4.0 and 7.5, and those under Quercus ilex stands between 4.3 and 8.5, whereas the pH range of the agricultural soils studied was narrower (7.6-8.4). The organic C data corresponding to the soil samples is currently being analyzed.