Tillage and Cover Crop Affected Soil Pore Characteristics in the Topsoil and Upper Subsoil.

Conservation tillage and cover crops are regarded as key elements in conservation agriculture. Many studies have assessed the impact of conservation tillage on soil structure but few studies have quantified the effect of combining conservation tillage with cover crop. This study examines the effect of these management tools on soil pore characteristics of a sandy loam soil in a long-term field trial. The tillage treatments (main plots) included direct drilling (D) harrowing to a depth of 8-10 cm (H) and mouldboard ploughing (MP). These have been applied for 10 years at the time of soil sampling. The cover crop treatments were subplot with cover crop (+CC) and without cover crop (-CC) and these treatments had been applied for 5 years in rotation with continuous spring barley. Minimally disturbed soil cores were taken from 4-8 cm, 12-16 cm and 18-27 cm depth intervals in the spring of 2012 before cultivation. Soil water retention and air permeability were measured for a range of matric potentials ranging from -10 to -300 hPa. Gas diffusivity was measured at -100 hPa. The  tillage treatments had little effect on  pore characteristics at 4-8 cm and 18-27 cm depth. At 12-16 cm depth, negative effects of reduced tillage treatments (D and H) were registered for total porosity and  air-filled porosity at  -100 kPa (i.e. >30 pores). There was no difference between tillage effects in terms of <30 µm pores. Generally, cover crop increased air-filled porosity at -10 kPa, air permeability and PO and reduced the value of blocked air porosity at all depths. However, cover crop did not affect total porosity. There was no significant interaction with tillage. Our results show that the cover crop had created continuous biopores and thereby improved the conditions for water and gas transport, and root growth. The cover crop had thus alleviated the effect of tillage pan compaction in all the tillage treatments.