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Soil organic matter depletion is a significant concern in agricultural soils, impacting crucial aspects of ecosystem health, especially soil properties such as fertility and soil moisture retention. Adopting sustainable soil management practices, such as cover crops, can mitigate this issue. In this study, we analyzed the soil organic carbon (SOC) content and quality in vineyards using two distinct management methods: permanent spontaneous cover crops and conventional tillage. Dissolved organic carbon (DOC) was quantified and chemically characterized using UV–visible spectroscopy. Our results showed an increase of 4.7 Mg C/ha in the carbon stock (50 cm depth) after 10 years of implementing vegetation covers compared with tilled soil. Additionally, cover crop management increased less humified soluble carbon in surface soil layers, while tillage transformed the solubilized carbon. This finding is important because tilled soil becomes more accessible to microbial degradation and leaching, which, in the long term, leads to a SOM content decrease. In conclusion, an increase in carbon stock was observed when using cover crops due to the incorporation of fresh organic matter, whereas tilled soils showed a depletion of carbon stock, including the mobilization of more stable carbon. [ABSTRACT FROM AUTHOR]

The increase in atmospheric CO2 levels and the advance of desertification due to soil degradation across our planet is becoming one of humanity's most serious concerns. The restoration and development of soil management techniques are becoming widespread tools to protect soils. The Sierra de Guadarrama National Park (Spain) is an area that has suffered historically severe deforestation, but it was reforested in an extensive program 50 years ago. In this study, an evaluation of the soils in the restored area was carried out. For this purpose, the chemical composition of the different soil organic matter fractions was characterized using infrared and UV-vis spectroscopies. The results showed a large increase in carbon stocks in the topsoil (0–10 cm) (about 30 Mg·ha−1 more than the area not reforested) after reforestation 50 years ago. There was also an increased level of transformation of organic carbon into resilient humic structures, which are resistant to degradation. Reforestation activities within the National Park have greatly increased the humification rates of organic matter, resulting in the accumulation of high-quality organic carbon. [ABSTRACT FROM AUTHOR]

The relationship between soil organic matter (SOM) content and organic molecular assemblages ( n-alkane/alkenes pairs and n-fatty acids) with soil water repellency (WR) in different sieve fractions (1-2, 0·25-1, 0·05-0·5 and <0·05 mm) was studied in sandy soils from the Doñana National Park (SW Spain) under four vegetation species: Quercus suber (QS), Pteridium aquilinum (PA), Pinus pinea (PP) and Halimium halimifolium (HH). The severity of soil WR [assessed according to the water drop penetration time (WDPT) test] was ordered according to the sequence QS > PA > PP > HH. A positive correlation was found between soil WR from each sieve fraction and SOM content. Most severe soil WR was detected in QS for all sieve fractions, followed by the finer fractions (<0·05 mm) from PA, PP and HH samples. The finer fraction had the highest SOM content, ranging between 20·9% (PP) and 46·9% (QS). Coarser PA, PP and HH soil fractions (1-2 mm) showed the highest long-chain-even C numbered fatty acids in the order PP > PA > HH. A significant correlation was observed between SOM content and the severity of soil WR in QS samples and finer fractions of soil under other vegetation (PA, PP and HH). Coarser fractions (1-2 mm) from PP, PA and HH 1-2 mm sieve fractions showed high severity of WR and relatively low SOM contents that could be explained by a low degree of evolution of the organic residues as seen by analytical pyrolysis, that is, higher alkane/alkene carbon preference index values and the presence of a higher diversity of fatty acid structures. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Pyrolysis applied to soil samples reveals the impact of soil forming factors. • Vegetation and climate play the chief role in soil organic matter composition. • High soil C levels are associated with slightly transformed lignin in soil. • Low SOC levels are related with non-methoxylated aromatic constituents. There is currently an active controversy about the variable influence of the factors involved in the total content and the quality of the soil organic matter (SOM), which translates into its resilience and stability against biodegradation, and importantly on the rates of release of CO 2 into the atmosphere. The aim of this work is to study the molecular composition of SOM in contrasting environments in order to evaluate the extent to which such conditions may affect SOM characteristics in addition to the levels of soil organic C (SOC). Up to 33 soils from different environmental scenarios of Spain were analysed by pyrolysis combined with gas chromatography mass spectrometry (Py-GC/MS). The 193 major pyrolysis compounds released from the soils were included in a chemostatistical study based in discriminant analysis to assess the impact of classical soil forming factors (i.e., climate, vegetation and geological substrate) in SOM content and composition. Improved van Krevelen diagrams were used to facilitate the recognition of different patterns in SOM composition dependent on soil forming factors. The results showed that the molecular composition of SOM varies systematically according to environmental factors, with a decreasing influence in the order: climate > vegetation > geological substrate. In addition, the total levels of SOM were also different depending on the environmental scenarios on these soils, suggesting both qualitative and quantitative control of soil C sequestration. [ABSTRACT FROM AUTHOR]