Land Use Effects on Organic Matter in Brown Soils of the Emilian Apennines

The study investigated organic carbon storage and tumover times and microbial activity in the epipedons of two soils that formed and evolved over a common parental substrate of sandstone and heterometric conglomerates in soil survey stations characterised by different land use and cover: natural mixed deciduous woodland, reforestation zones planted with Douglas Fir (Pseudotsuga menziesii Franco) and plots cultivated with alfalfa (Medicago sativa L.). AlI profiles displayed a degree of reaction (pH) ranging ftom neutral to alkaline. The physicochemical and biological characteristics of the surface horizons of the Monte delle Formiche profile (Thapto-eutric Haplic Cambisols) under mixed deciduous forest cover were compared to those of tilled soil planted with alfalfa; similarly, the forest profile of Monte Zena (Calcaric Cambisols), again under mixed deciduous cover, was compared with soils ftom a nearby reforestation area planted with Douglas Fir and an adjacent plot of land planted with alfalfa. The content of total organic carbon (Corg), extractable carbon (Cextr) and humic (CRA) and fulvic (CFA) acids decreased with increases in profile depth and the value of these parameters was greater in soils under mixed deciduous cover than in those under coniferous cover; the lowest values were to be found in cultivated soils. The humification index of forest soils showed a lower degree of humification of organic matter in the A2 horizons of the epipedon as compared to the Al horizons. The soil humification index (HI) in the reforested and cultivated areas is close to the typical values found in single-crop agricultural environments. The MF forest soil under mixed woodland cover displayed higher values for alI C fractions, including microbial C (Crnie), as compared to the adjacent cultivated site (MFcult); the much higher level of potentially mineralizable C (Co) indicates a greater amount of material readily available for the microbial biomass. The tumover time (l/K) calculated for forest and tilled soils is similar in the surface horizon, whereas tumover occurs more rapidly in the A2 horizon of forest as compared to MFcult soil (depth of 5-10 cm). However, the low microbial quotient and high metabolic quotient (qC02) indicate that the surface horizons of the MF so il under mixed forest cover are currently in a stage of development and evolution definable as paraclimax. AH organic and biological C parameters of soils in the Monte Zena station were observed to be low; the epipedons of the MZ forest profile display a lower content of Corg as compared to the MF forest soil, while the parameters relating to microbial biomass activity suggest conditions of stability (climax). The Douglas Fir reforestation zone showed the lowest values of Crnie, a low Crnie/Corg ratio and high qCOz, especiaHy in the A2 horizon of the epipedon. The increase in qCOz may be seen as the response of the microbial biomass to changes in the quality of the organic C of plant residues incorporated into the soil - as reflected by the low degree of humification of organic matter (totallevel of humification 75%) - and signals a stress condition. The cultivated soils of the two stations reveal a situation of disturbance, mainly ascribable to farrning practices, which manifests itself in system stability as far as the living fraction of the soi! is concemed, though the samples taken at both depth intervals showed the lowest content of humidified Corg, in association with high humification indexes.