Tillage System and Cover Crop Effects on Soil Quality: II. Pore Characteristics

Information about the quantitative effect of conservation tillage combined with a cover crop on soil structure is still limited. This study examined the effect of these management practices 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 to 10 cm (H), and moldboard plowing (MP). The cover crop treatments were subplot with cover crop (+CC) and without cover crop (-CC). Minimally disturbed soil cores were taken from the 4- to 8-, 12- to 16-, and 18- to 27-cm depth intervals in the spring of 2012 before cultivation. Soil water retention and air permeability were measured for matric potentials ranging from -1 to -30 kPa. Gas diffusivity was measured at -10 kPa. Computed tomography (CT) scanning was also used to characterize soil pore characteristics. At the 4- to 8- and 18- to 27-cm depths, pore characteristics did not differ significantly among tillage treatments. At the 12- to 16-cm depth, negative effects of reduced tillage (D and H) were recorded for total porosity and air-filled porosity at -10 kPa (that is, >30-mu m pores). Generally, the use of a cover crop increased air-filled porosity at -10 kPa, air permeability, and pore organization and reduced the value of blocked air porosity at all depths for all tillage treatments. Our results show that the cover crop created continuous macropores and in this way improved the conditions for water and gas transport and root growth. The cover crop thus alleviated the effect of tillage pan compaction in all tillage treatments.