Hydraulic resistance in puddled rice soils: measurement and effects on water movement. uri icon

abstract

  • A technique is presented to measure in-situ infiltration rate and pressure head gradients within a puddled rice soil. Measurements at 33 sites within a small 0.1 ha plot indicated unsaturated flow conditions in the non-puddled subsoil. The least permeable layer within the profile, as determined by the greatest gradient in pressure head, was found to be at the interface of puddled topsoil (0-15 cm) and non-puddled subsoil. Average thickness of this layer was about 5 cm. Hydraulic resistance of the least permeable layer at all measurement sites was lognormally distributed with an average value of 209 days, and 95% confidence limits at 156 and 262 days. Corresponding average hydraulic conductivity was 0.36 mm day-1 with 95% confidence limits at 0.27 and 0.45 mm day-1. Measured pressure heads in the subsoil showed good agreement with values predicted from comparison of measured hydraulic resistance in the puddled surface soil and non-puddled subsoil. Puddling reduced infiltration rate by a factor of 500.

publication date

  • 1992
  • 1992
  • 1992