Tuesday, November 14, 2006

Tillage Effects on Surface Soil Properties, Crusting, and Sorghum Emergence.

Robert C. Schwartz, Jourdan M. Bell, and R. Louis Baumhardt. USDA-ARS Conservation and Production Res. Lab., PO Drawer 10, 2300 Experiment Station Rd., Bushland, TX 79012

No tillage practices can reduce evaporation and increase soil water storage for improved soil water availability in semi-arid regions. However, the formation and maintenance of a seal at the soil surface under no tillage has been implicated in reducing infiltration as compared with limited tillage practices that periodically destroy the crust. We investigated the influence of tillage on crust thickness, penetrometer resistance, and sorghum [Sorghum bicolor (L.) Moench] emergence after an intense precipitation event (~100 mm) that occurred two days after planting. The study was carried out in six plots on Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll). These plots have been cropped under a wheat (Triticum aestivum L.)-sorghum-fallow rotation with no tillage (NT) and stubble-mulch tillage (ST) since 1997. Grain sorghum was planted 8 June, 2005 at a rate of 8.4 seed m-2 and a row spacing of 0.76 m. All measurements were carried out in residue-free areas within the sorghum row. Penetration resistance was measured on crusts using a flat point handheld penetrometer. Soil organic carbon and wet aggregate stability were also measured for soil samples collected at 0 - 30 mm. Sorghum emergence 15 days after planting was 56% greater (P<0.05) for NT as compared to ST plots. Average field penetration resistance of ST surfaces (3.59 MPa) were significantly (P<0.05) greater than NT surfaces (2.85 MPa) nine days after planting. Despite recent tillage, mean crust thickness was significantly greater under ST (13 mm) as compared with NT (9 mm). Soil organic carbon was 46% greater for NT (P<0.05) as compared with ST, however there were no tillage effects on the fraction of water stable aggregates and mean weight diameter. Recent tillage combined with lower organic carbon contents of the ST plots permitted the development of thicker, stronger crusts which reduced sorghum emergence.