|Evett, Steven - Steve|
Submitted to: International Workshop Characterization and Measurement Hydraulic Propertie
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/1997
Publication Date: N/A
Technical Abstract: Long term tillage effects may be effectively characterized on the basis of changes in soil surface hydraulic properties. These properties directly influence infiltration as well as the movement of soil water to the surface during drying. We measured surface soil hydraulic properties on no-till (NT) and conventional (stubble mulch) tillage (CT) plots; each of which was sfarmed with either a wheat-sorghum-fallow (WSF) or a wheat fallow (WF) rotation. The plots had been in the same treatments for 12 years. Tension infiltrometers were used to measure steady state infiltration rates at four heads, h, (nominally -2.0-, -1.5-, -1.0-, and -0.5-kPa, applied in that order); resulting in estimates of hydraulic conductivity, K(h). Both single- and multiple-reservoir infiltrometers were constructed. The multiple-reservoir infiltrometer allowed completion of infiltration to steady state at four tensions without disturbance of flow regime or of soil lcontact due to re-filling of reservoirs. Hanging water column and pressur plate techniques were used to measure soil water retention values, theta(h), on undisturbed core samples. Parameter theta was not well estimated by a nonlinear optimization used to find the parameters Ks and alpha in Wooding's equation for steady state flow; so was estimated as the mean of values satisfying Wooding's equation for any two tensions and flow rates. The K(h) and theta(h) data were fitted to Mualem's and van Genuchten's forms for the hydraulic conductivity and retention curves, respectively, using the RETC program (r**2 >/= 0.99). The fitted water retention curves showed marked difference between NT and CT treatments.