Soil Science Society of America Journal Soil Sci. Soc. Am. J. 81:392–403 doi:10.2136/sssaj2016.07.0221 Received 18 July 2016. Accepted 12 Jan. 2017. *Corresponding author (lars.munkholm@agro.au.dk). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved. Eleven Years’ Effect of Conservation Practices for Temperate Sandy Loams: II. Soil Pore Characteristics Soil & Water Management & Conservation Conservation agriculture (CA) is regarded by many as a sustainable inten- sifcation strategy. Minimal soil disturbance in combination with residue retention are important CA components. This study examined the long-term effects of crop rotation, residue retention, and tillage on soil pore character- istics of two Danish sandy loams. Rotation R2 is a rotation of winter crops (mainly cereals) with residues retained, rotation R3 a mix of winter and spring crops (mainly cereals) with residues removed, and rotation R4 the same mix of winter and spring crops, but with residues retained. Each rota- tion included the tillage treatments: moldboard plowing to 20-cm depth (MP), harrowing to 8- to 10-cm depth (H) and direct drilling (D). Soil cores were taken from the topsoil (4–8, 12–16, 18–27 cm) in mid-autumn 2013 and early spring 2014. Water retention, air permeability, and gas diffusivity was determined for the frst two depths (100-cm 3 cores), and air permeability for the 18- to 27-cm depth (250-cm 3 cores). Moldboard plowing resulted in the best soil quality at two upper depths with higher total porosity, air-flled porosity, air permeability, and gas diffusivity compared with reduced tillage. For instance, the volume of pores > 30 µm was more than 0.03 m 3 m -3 larger for MP than for D in spring 2014 at the 4- to 8-cm depth. At the 18- to 27-cm depth, direct drilling resulted in a better air permeability and pore continuity index (e.g., air permeability of 18.2 and 11.2 mm 2 for D and MP, respective- ly at −10 kPa for the Foulum location). Residue retention, especially when combined with direct drilling, increased total porosity, air-flled porosity, air permeability, and gas diffusivity and decreased blocked air porosities. Our results suggest residue management can be used to alleviate the negative effects of reduced tillage on soil structural quality. Abbreviations: CA, conservation agriculture; D, direct drilling; H, harrowing to an 8- to 10-cm depth; MP, moldboard plowing to a 20-cm depth; PO, pore organization. S ustainability of agricultural practices is of growing concern because of in- creased food, feed and fuel demand, and the impact on the environment and climate change and its consequences (European Commission, 2015; FAO, 2017). Proper soil management is a prerequisite for sustainable agriculture and therefore there is strong focus on soil management strategies to mitigate soil degradation and improve soil quality (Lal, 2015). Conservation agriculture has been suggested as a means to improve the delivery of ecosystem services from agricultural systems (Palm et al., 2014). Minimal soil disturbance, crop rotation, and residue retention are regarded as the key components of CA (Torres et al., 2001; Verhulst et al., 2010; Wall, 2007). According to the EU Thematic Strategy (http://ec.europa.eu/environment/soil/three_en.htm), one of the specific soil functions for food production is: “the pathway through which water and nutri- ents move to roots, whether from soil reserves or from external inputs” (Powlson et al., 2011). The key structural part of soil that fulfills this specific function is the soil pore network. Lotfollah Abdollahi Department of Agroecology Aarhus University Research Centre Foulum P.O. Box 50 DK-8830 Tjele Denmark Faculty of Agriculture Payame Noor University (PNU) P.O. Box 19395-3697 Tehran, Iran Lars Juhl Munkholm* Department of Agroecology Aarhus University Research Centre Foulum P.O. Box 50 DK-8830 Tjele Denmark Core Ideas • Long-term effects of tillage, rotation, and residue management studied. • Residue retention increased porosity, air permeability, and gas diffusivity. • Residue retention alleviated negative effects of reduced tillage on soil pores. • Moldboard plowing caused best topsoil (0-20 cm depth) quality. • Direct drilling resulted in highest air permeability at the 18- to 27-cm depth. Published April 20, 2017