Knowledge, conservation and sustainable use of soil: agricultural chemistry aspects

Soil is an environmental resource and plays ecological, social and economic functions which are fundamental for the life. To guarantee its availability to future generations, soil resource needs sustainable management. The CEC Thematic Strategy for Soil Protection identifies a series of soil degradation processes or threats, which must be identified and combated. These include erosion, decline in organic matter, local and diffuse contamination, sealing, compaction, decline in biodiversity, salinisation, floods and landslides. With respect to management of contamination with potentially toxic elements, an approach based on the identification and quantification of the various forms or, at least, the main pools, in which contaminants occur in soil, is envisaged. The residence time of an element in soil depends, indeed, by the mobility of its predominant forms. Speciation studies provide information on the mobility and biological availability of contaminants, and seek to assess not simply the contamination level, but rather the risk/toxicity of a polluted soil and to predict its reduction after application of remediation techniques. Soil degradation is often associated with a decrease in the organic matter content, mainly caused by soil use change and global warming. Improving the accumulation of organic matter in soil or contrasting its reduction has positive effects on soil and water quality, crop yields, biodiversity and climate leading to a reduction of green-house gas emissions from soil to the atmosphere. In order to obtain a real accumulation of organic matter in soil, it is not sufficient to temporarily increase its total content, but it is necessary to favour the main processes which govern organic matter stabilization. This requires an approach at both molecular and multidisciplinary level. The reforestation of agricultural and highly degraded soils or conservative agronomic practices, such as the use of humified compounds characterized by an important hydrophobic component, the incorporation of crop residues, no-tillage, and crop rotations may have beneficial effects and increase organic matter levels, through the selective preservation of biochemical compounds more resistant to degradation, the slowing down of the turnover of organic matter already present in soil, physical and chemical protection due to aggregation and interaction of organic matter with the mineral phase.