No till soil organic carbon sequestration could be overestimated when slope effect is not considered.

No tillage (NT) soil management has been considered a strategy for the implementation of environmental sustainability and a possible tool of soil organic carbon (SOC) sequestration. Considering the wide range of data on SOC change after NT application in relation to conventional tillage (CT) in different studies, further researches are needed over a diverse range of soil and climate before a proper estimation of the benefits can be provided by the NT. A data set composed of cereal cropping system studies, comparing the SOC content under CT and NT was compiled from the literature using the scientific repositories "Scopus" and "Science direct". This aims to i) discriminate and quantify the variation of SOC in relation to morphology (Flat area (FA) and Slope Area (SA)) and climates (Aridity index (Ai)); ii) provide a reliable forecast of C sequestration by NT in a specific environment. The results from collected datasets showed that SOC ratio between NT and CT was higher in sloping than flat areas and was also in correlation with the Ai. The average annual increase of SOC in NT in comparison to CT was 0.32 Mg ha-1y-1 and 0.21 Mg ha-1y-1 for SA and FA, respectively. The regression of the relative ratio (RRNT/CT) against Ai both for FA and SA showed a high statistical significance for FA. For SA the lack of significance is due to no response of the dependent variables to Ai changes and to the prevalent effect that NT has on the soil C erosion processes. These results highlighted that in SA, the SOC sequestration by NT is overestimated. These results provide concrete examples of the importance to discriminate soil morphology and climate when recommending NT soil management for soil C sequestration in order to individuate areas where NT can maximize its potentiality as a mitigation tool.

Carbon stock increases up to old growth forest along a secondary succession in Mediterranean island ecosystems.

The occurrence of old-growth forests is quite limited in Mediterranean islands, which have been subject to particularly pronounced human impacts. Little is known about the carbon stocks of such peculiar ecosystems compared with different stages of secondary succession. We investigated the carbon variation in aboveground woody biomass, in litter and soil, and the nitrogen variation in litter and soil, in a 100 years long secondary succession in Mediterranean ecosystems. A vineyard, three stages of plant succession (high maquis, maquis-forest, and forest-maquis), and an old growth forest were compared. Soil samples at two soil depths (0-15 and 15-30 cm), and two litter types, relatively undecomposed and partly decomposed, were collected. Carbon stock in aboveground woody biomass increased from 6 Mg ha-1 in the vineyard to 105 Mg ha-1 in old growth forest. Along the secondary succession, soil carbon considerably increased from about 33 Mg ha-1 in the vineyard to about 69 Mg ha-1 in old growth forest. Soil nitrogen has more than doubled, ranging from 4.1 Mg ha-1 in the vineyard to 8.8 Mg ha-1 in old growth forest. Both soil parameters were found to be affected by successional stage and soil depth but not by their interaction. While the C/N ratio in the soil remained relatively constant during the succession, the C/N ratio of the litter strongly decreased, probably following the progressive increase in the holm oak contribution. While carbon content in litter decreased along the succession, nitrogen content slightly increased. Overall, carbon stock in aboveground woody biomass, litter and soil increased from about 48 Mg ha-1 in the vineyard to about 198 Mg ha-1 in old growth forest. The results of this study indicate that, even in Mediterranean environments, considerable amounts of carbon may be stored through secondary succession processes up to old growth forest.

Real cover crops contribution to soil organic carbon sequestration in sloping vineyard.

The research focused on the evaluation of the effect of soil erosion processes on SOC sequestration rate after 5 years of cover crop soil management in Mediterranean vineyards (Sicily, Italy). Two paired sites, one in a sloping area and another one in a contiguous flat area, were chosen. The vineyard soils of the two plots of each paired site were managed with conventional soil tillage (CT) and Vicia faba cover crop (CC) the preceding 5 years. SOC was measured in three points along the slope (top, middle and foot parts) and in the flat area. Results showed that in the slope area the highest SOC content was found in CC management, with an average value of 9.52 ±â€¯0.34 g kg-1, whereas the SOC content under CT was 8.74 ±â€¯0.20 g kg-1. In the flat vineyard, the SOC ranged from 9.88 ±â€¯0.11 g kg-1 to 10.47 ±â€¯0.20 g kg-1 under CT and CC, respectively. The SOC increase was 6% in the flat area and 9% in the sloping vineyard after five years since CC management adoption. The higher C sequestration rates in the sloping vineyard in comparison to the flat area could be attributed to the role of CC to prevent sediment and nutrient erosion. These results were compared with those by reference works and with the results of 39 vineyards paired-sites. Findings demonstrated that C sequestration rate is strongly correlated to slope gradient and the C sequestration per se due to the effect of added C input by the cover crop is overestimated.

The impact of soil erosion on soil fertility and vine vigor. A multidisciplinary approach based on field, laboratory and remote sensing approaches.

Soil erosion processes in vineyards, beyond surface runoff and sediment transport, have a strong effect on soil organic carbon (SOC) loss and redistribution along the slope. Variation in SOC across the landscape can determine differences in soil fertility and vine vigor. The goal of this research was to analyze the interactions among vines vigor, sediment delivery and SOC in a sloping vineyard located in Sicily. Six pedons were studied along the slope by digging 6 pits up to 60cm depth. Soil was sampled every 10cm and SOC, water extractable organic carbon (WEOC) and specific ultraviolet absorbance (SUVA) were analyzed. Erosion rates, detachment and deposition areas were measured by the pole height method which allowed mapping of the soil redistribution. The vigor of vegetation, expressed as Normalized Difference Vegetation Index (NDVI), derived from high-resolution satellite multispectral data, was compared with measured pruning weight. Results confirmed that soil erosion, sediment redistribution and SOC across the slope was strongly affected by topographic features, slope and curvature. The erosion rate was 16Mgha-1y-1 since the time of planting (6years). SOC redistribution was strongly correlated with the detachment or deposition areas as highlighted by pole height measurements. The off-farm SOC loss over six years amounted to 1.2MgCha-1. SUVA254 values, which indicate hydrophobic material rich in aromatic constituents of WEOC, decreased significantly along the slope, demonstrating that WEOC in the detachment site is more stable in comparison to deposition sites. The plant vigor was strongly correlated with WEOC constituents. Results demonstrated that high resolution passive remote sensing data combined with soil and plant analyses can survey areas with contrasting SOC, soil fertility, soil erosion and plant vigor. This will allow monitoring of soil erosion and degradation risk areas and support decision-makers in developing measures for friendly environmental management.

Agricultural land abandonment in Mediterranean environment provides ecosystem services via soil carbon sequestration.

Abandonment of agricultural land leads to several consequences for ecosystem functions. Agricultural abandonment may be a significant and low cost strategy for carbon sequestration and mitigation of anthropogenic CO2 emissions due to the vegetation recovery and increase in soil organic matter. The aim of this study was to: (i) estimate the influence of different Soil Regions (areas characterized by a typical climate and parent material association) and Bioclimates (zones with homogeneous climatic regions and thermotype indices) on soil organic carbon (SOC) dynamics after agricultural land abandonment; and (ii) to analyse the efficiency of the agri-environment policy (agri-environment measures) suggested by the European Commission in relation to potential SOC stock ability in the Sicilian Region (Italy). In order to quantify the effects of agricultural abandonment on SOC, a dataset with original data that was sampled in Sicily and existing data from the literature were analysed according to the IPCC (Intergovernmental Panel on Climate Change) methodology. Results showed that abandonment of cropland soils increased SOC stock by 9.03MgCha-1 on average, ranging from 5.4MgCha-1 to 26.7MgCha-1 in relation to the Soil Region and Bioclimate. The estimation of SOC change after agricultural use permitted calculation of the payments for ecosystem service (PES) of C sequestration after agricultural land abandonment in relation to environmental benefits, increasing in this way the efficiency of PES. Considering the 14,337ha of abandoned lands in Sicily, the CO2 emission as a whole was reduced by 887,745Mg CO2. Therefore, it could be concluded that abandoned agricultural fields represents a valid opportunity to mitigate agriculture sector emissions in Sicily.

Understanding the role of soil erosion on co2-c loss using (13)c isotopic signatures in abandoned Mediterranean agricultural land.

Understanding soil water erosion processes is essential to evaluate the redistribution of soil organic carbon (SOC) within a landscape and is fundamental to assess the role of soil erosion in the global carbon (C) budget. The main aim of this study was to estimate the C redistribution and losses using (13)C natural abundance. Carbon losses in soil sediment, dissolved organic carbon (DOC) and CO2 emission were determined. Four bounded parallel plots were installed on a 10% slope. In the upper part of the plots, C3soil was replaced with C4soil. The SOC and δ(13)C were measured after 145.2mm rainfall in the upper (2m far from C4strip), middle (4m far from C4strip) lower (6m far from C4strip) trams of the plot and in the sediments collected in the Gerlach collector at the lower part of the plot. A laboratory incubation experiment was performed to evaluate the CO2 emission rate of soils in each area. OC was mainly lost in the sediments as 2.08g(-)(2) of C was lost after 145.2mm rainfall. DOC losses were only 5.61% of off-site OC loss. Three months after the beginning of the experiment, 15.90% of SOC in the upper tram of the plot had a C4 origin. The C4-SOC content decreased along the 6m length of the plot, and in the sediments collected by the Gerlach collector. CO2 emission rate was high in the upper plot tram due to the high SOC content. The discrimination of CO2 in C3 and C4 portion permitted to increase our level of understanding on the stability of SOC and its resilience to decomposition. The transport of sediments along the plot increased SOC mineralization by 43%. Our study underlined the impact of rainfall in C losses in soil and water in abandoned Mediterranean agriculture fields and the consequent implications on the C balance.