Impacts of long-term wheat straw management on soil hydraulic properties under no-tillage

Crop residues left on the soil surface conserve soil and water, but residue impacts on near-surface soil hydraulic properties have not been widely studied. Therefore, soil hydraulic properties were determined under uncropped no-tillage (NT) plots receiving three levels of wheat (Triticum aestivum L.) straw mulch (0, 8, and 16 Mg ha(-1) yr(-1)) application for 10 consecutive yr on a Crosby silt loam (fine, mixed, active, mesic Aeric Epiaqualfs) in central Ohio. Water infiltration rates, earthworm population, saturated hydraulic conductivity (Kat), soil water retention (SWR), total porosity, and pore-size distribution were determined and unsaturated hydraulic conductivity was estimated from SWR and Kat data. Mulching significantly impacted hydraulic properties in the 0- to 3-cm soil depth (P < 0.01), but water infiltration rate was unaffected. Earthworm counts were 0 m(-2) in the unmulched treatment, 158 52 m(-2) (mean +/- SD) in treatments with 8 Mg ha(-1) yr(-1) of straw, and 267 58 m(-2) in those with 16 Mg ha(-1) yr(-1) of straw. Mulched treatments had a Kat 123 times greater and retained 40 to 60% more water between 0 and -1500 kPa than the unmulched treatment. Soil porosity increased by 28% under 8 Mg ha(-1) yr(-1) of straw and by 44% under 16 Mg ha(-1) yr(-1) in the 0- to 3-cm depth compared with the unmulched treatment. Pore volume of macro- and mesopores was greater in mulched treatments and that of fine mesopores was greater in the unmulched treatment in the 0- to 3-cm depth. Straw mulching appears to be a viable practice to improve near-surface hydraulic properties in long-term NT soils, although residues may not increase water infiltration rates.