Soils are the biggest carbon store in the world (1500 Gt, e.g. 1.5 × 1021 g). The European Commission indicates the accounting of soil organic carbon (SOC) variations in space and time as the first step in the strategy for soil protection. It is indeed necessary in evaluating the risk of soil organic matter decline and soil biodiversity decline, and when evaluating the role played by soils in global CO2 accounting. Previous maps of SOC variations in Italy did not consider the direct effect of climate. There is a marked inter-dependence between SOC and climate. SOC increases with the increase in precipitations and decreases with a rise in temperatures. It is also known that land use and management have a bigger impact on SOC than climate. The aim of this work is to understand to what extent the SOC variations occurring in Italy from 1961 to 2008 could be explained by climate change. The soil database of Italy was the source of information for SOC content: 17,817 observations (3082 before and 14,735 after 31 Dec 1990). SOC content was referred to the first 50 cm of soil depth, one single data obtained by weighted horizon thickness. SOC content was expressed as percentage by weight (dag kg− 1) analyzed by the Walkley–Black procedure and converted to ISO standard. The CRA–CMA (Research Unit for Climatology and Meteorology Applied to Agriculture) database was the source of information for climatic data. We considered the mean annual temperature (MAT) and mean value of total annual precipitation (MAP) of the two periods 1961–1990 and 1991–2006, and we mapped them by regression kriging with elevation and latitude as predictors. The climate change between the two periods was characterized by a general MAT increase, which was greater at lower altitudes and higher latitudes. The precipitation generally decreased, with some local exceptions. Some linear regression analyses were used to investigate the relationship between SOC content and climate/land use. Temperatures had most relevant impact on SOC with an inverse correlation. SOC content was directly correlated with precipitations on arable lands and inversely in forests and meadows. Two general multiple linear regression analyses considered all the pedogenesis factors and: either by time periods (1979–1990; 1991–2009), model 1; or by MAT and MAP, model 2. The two models both had low precision (multiple R-squared = 0.26–0.27; RMSE = 1.42; IoA = 0.61), but very different accuracies. Model 1 correctly predicted the mean SOC values for the 3 land uses in the 2 periods, detecting a significative decrease in all three land uses. Model 2 was not accurate every time. SOC decreases estimated with model 2 were always significatively lower than the observed ones. Model 2 did not estimate a significative SOC decrease in forests. Climate change had a general low influence on SOC variations. The relatively higher climatic influence occurred in meadows and in agricultural areas with a moderate or high MAP decrease (<−100 mm/y) and a moderate to high MAT increase (> 0.62 °C). Other changes, probably linked to land management, need to be investigated to explain SOC variations.

Abstract
Land use strongly influences soil properties and unsuitable practices lead to degradation of soil and environmental quality. The aim of this study was to assess the impact of different land uses on some chemical properties of soils developed from Pliocene clays, within hilly environments of central and southern Italy. The areas investigated are located in Vicarello di Volterra (Pisa, Tuscany), S. Quirico d’Orcia (Siena, Tuscany) and Soveria Simeri (Catanzaro, Calabria). Within each area different land uses were compared, including a natural ecosystem (Mediterranean bush), a perennial grass or pasture and an intensive crop (wheat, as monoculture or in rotation). The soils were sampled at 0.0–0.1, 0.1–0.2 and 0.2–0.4 m depth and analysed for particle size, pH, bulk density, cation exchange capacity and exchangeable cations, total organic carbon (TOC) and humified carbon (HC) concentrations, organic carbon stock and total N. The stratification ratio of soil organic carbon was calculated to characterize soil organic carbon distribution with depth. At all sites, soil under Mediterranean bush contained the largest amounts of TOC (as both concentration and stock), HC, total N and exchangeable K, together with the highest cation exchange capacity and the lowest pH values. The decrease in soil OC stock with land use change from natural to agricultural ecosystem was 65–85% to 0.1 m depth, 55–82% to 0.2 m depth and 44–76% to 0.4 m depth, with the lowest decrements for perennial grass from S. Quirico and the highest decrement for continuous wheat from Soveria Simeri. Continuous wheat cropping, based on conventional tillage, proved to be the least sustainable land use. At Soveria Simeri, the organic carbon content under pasture was not significantly larger than under wheat cultivation, probably because of grazing mismanagement; however, organic carbon under pasture was more humified. At S. Quirico, the perennial grass resulted in a significant increase in soil organic carbon at the soil surface relative to the wheat cultivation, while at Vicarello no differences were observed between alfalfa/wheat rotation and perennial grass. Our results lead to the questioning of sustainability of intensive cereal farming and uncontrolled grazing in the considered environments, emphasizing the need for greater attention to conservative land managements.

Research highlights
▶ Arable farming and unmanaged grazing severely limit soil OC storage in sloping Mediterranean lands. ▶ Loss of soil organic matter by cultivation is reflected in a decline in soil quality. ▶ Conservative agricultural managements are needed to counteract land degradation.

Keywords
Continuous wheat; Land use; Mediterranean bush; Organic carbon; Pliocene clays

Abstract
Soils contain about three times the amount of carbon globally available in vegetation, and about twice the amount in the atmosphere. However, soil organic carbon (SOC) has been reduced in many areas, while an increase in atmospheric CO2 has been detected. Recent research works have shown that it is likely that past changes in land use history and land management were the main reasons for the loss of carbon rather than higher temperatures and changes of precipitation resulting from climate change. The primary scope of this work was to estimate soil organic carbon stock (CS) variations in Italy during the last three decades and to relate them to land use changes. The study was also aimed at finding relationships between SOC and factors of pedogenesis, namely pedoclimate, morphology, lithology, and land use, but also at verifying the possible bias on SOC estimation caused by the use of data coming from different sources and laboratories. The soil database of Italy was the main source of information in this study. In the national soil database is stored information for 20,702 georeferentiated and dated observations (soil profiles and minipits) analysed for routine soil parameters. Although the observations were collected from different sources, soil description and analysis were similar, because all the sources made reference to the Soil Taxonomy and WRB classification systems, and soil analyses followed the Italian official methods. Besides horizon description and analysis, soil observations had a set of site information including topography, lithology, and land use. The SOC and bulk density referred to the first 50 cm, thus CS was calculated on the basis of the weighted percentage of SOC, rock fragments volume, and bulk density. A set of geographic attributes were considered to spatialize point information, in particular, DEM (100 m) and derived SOTER morphological classification, soil regions (reference scale 1:5,000,000) and soil systems lithological groups (reference scale 1:500,000), soil moisture and temperature regimes (raster maps of 1 km pixel size), land cover (CORINE project, reference scale 1:100,000) at three reference dates: years 1990 and 2000, and an original update to 2008, obtained with field point observations. The interpolation methodology used a multiple linear regression (MLR). CS was the target variable, while predictive variables were the geographic attributes. Basic statistical analysis was performed first, to find the predictive variables statistically related to CS and to verify the bias caused by different laboratories and surveys. After excluding the biased datasets, the best predictors were selected using a step-wise regression method with Akaike Information Criterion (AIC) as selection and stop criterion. The obtained MLR model made use of the following categorical attributes: (i) decade, (ii) land use, (iii) SOTER morphological class, (iv) soil region, (v) soil temperature regime, (vi) soil moisture regime, (vii) soil system lithology, (viii) soil temperature, (ix) soil aridity index (dry days per year), and, (x) elevation. The interaction between decade and land use variables was also considered in the model. Results indicated that CS was highly correlated with the kind of main type of land use (forest, meadow, arable land), soil moisture and temperature regimes, lithology, as well as morphological classes, and decreased notably in the second decade but slightly increased in the third one, passing form 3.32 Pg, to 2.74 Pg and 2.93 Pg respectively. The bias caused by the variables like “laboratory” and “survey source” could be as large as the 190%.
Keywords Carbon sequestration - Land use change - Factor of pedogenesis - Multiple regression

Tra i processi che conducono alla degradazione dei suoli, la minaccia costituita dal declino del carbonio organico è particolarmente rilevante, tanto che l’Unione Europea la ha indicata tra le priorità nella direttiva quadro sulla protezione del suolo. Studi recenti negli USA evidenziano un aumento significativo del carbonio organico nelle ultime decadi, come conseguenza della adozione e diffusione di pratiche agricole conservative (no/minimum tillage). Alcune esperienze nazionali e locali in Italia indicano una scarsa dotazione di sostanza organica nei suoli italiani. Il Ministero delle Politiche Agricole e Forestali ha finanziato un progetto denominato “Banca dati dei suoli d’Italia” (BADASUOLI), finalizzato alla raccolta, e all’integrazione nazionale delle informazioni pedologiche regionali e alla realizzazione di una banca dati dei suoli d’Italia. I dati di rilevamenti condotti in tutta Italia sono stati raccolti, armonizzati e correlati con una base geografica di riferimento, in modo tale da realizzare un geodatabase, cioè un sistema informativo che collega la banca dati alfanumerica con quella geografica. Sono attualmente presenti in banca dati molti milioni di records, relativi ad oltre 33.000 siti di rilevamento, e le informazioni geografiche dei suoli a diverse scale di riferimento (da 1:5.000.000 a 1:500.000).