Nano to macro pore structure changes induced by long-term residue management in three different soils

The use of crop residues for bioenergy production has gathered much attention in recent years. For this reason, the potential detrimental effects on soil quality caused by their removal need to be carefully evaluated before this practice becomes widely used. Data from a long-term field experiment on residue management in three contrasting soils (clay, sandyloam and sandy) were analysed in order to understand crop residue effects on soil organic carbon stocks. In addition, since soil structure is known to be a sensitive descriptor of soil quality, different techniques were combined to investigate a wide range of pore sizes (from 0.25 nm to 2.5 mm) and pore morphology. Forty-three years of crop residue incorporation led to a significant increase in the organic carbon content of the three soils. The clay and sandy-loam soils were the most effective in retaining organic carbon as they exhibited the highest absolute increases. The sandy soil showed a residue-induced increase in organic carbon content, indicating that some protection mechanisms may act in the long term even in soils with a scarce ability to protect organic carbon from degradation. Residues modified the soil structure, inducing an increase in total pore volume as measured by the core method, although their effect was not found in all pore size classes. Residues decreased mesoporosity (30–75mm), while their effect on macropores (>75mm) was in terms of shape, increasing the irregular and elongated pores rather than their size frequency. The results thus showed a limited overall effect of residues on soil structure. However, even minor pore network changes could affect other important soil properties such as water movement, solute transport and gas exchanges.