The unsaturated hydraulic conductivity function for soil can be calculated directly from a moisture retention and single measurement of at some water content. If the represented by ψ = ψc (θ/θa)−b, where is air entry potential, θ, saturated content, b an emperically determined constant, then given k ks (θ/θs)2b+3, conductivity. Agreement using this procedure with experimentally conductivities five samples was found to least as good other calculation procedures.

Hydraulic conductivity ( K ) in the soil and xylem declines as water potential Ψ declines. This results a maximum rate of steady‐state transpiration E crit corresponding minimum leaf at which has approached zero somewhere soil–leaf continuum. Exceeding these limits causes transport to cease. A model determined whether point hydraulic failure (where = 0) occurred rhizosphere or components Below threshold root:leaf area R : L ), loss limited . Above threshold, from cavitation was limiting. The...

A simple equation has been developed for describing the bidirectional reflectance of some vegetative canopies and bare soil surfaces. The describes directional as a function zenith azimuth view angles solar angle. works simulated field measured red IR under clear sky conditions. Hemispherical can be calculated coefficients by integrating over hemisphere angles. single estimating was obtained using relationships between medium rough distributions. many useful applications such providing lower...

Abstract Temperature rise, measured a short distance from line heat source, can be used to determine the volumetric specific of soil and other materials. Volumetric is linearly related inverse temperature rise. The purpose this note describe construction performance device for measuring using source method. was constructed two hypodermic needles, 0.813 mm in diam. 28 long, spaced 6 apart. One needle contained heater thermocouple. rise pulses given were with coefficientof variation (CV) on...

Simulation of soil temperatures under forest and range fires requires reliable estimates thermal properties over a from ambient to about 600°C. We measured conductivity samples differing in texture, bulk density, water content, temperature then fit the results with modification de Vries equation. Thermal increases dramatically moist soil, reaching values 3 5 times value at 90°C. The modified theory agreed well data low temperature, provided an upper boundary for measurements higher...

Abstract The enhancement of water vapor diffusion in soil resulting from a temperature gradient was determined using transient state thermal conductivity measurement. method Parikh et al. (1979) adapted for this study to allow measurement the as function temperature, content, and pressure. data allowed separation thermally induced latent heat transport. Both mechanistic factor η Philip de Vries phenomenological β Cary are calculated slope relationship between reciprocal relative factor,...

Abstract Water potential is one of the most important physical properties soil but remains among difficult to measure reliably. We describe a water activity meter that can be conveniently used potentials in soils ranging wetness from near saturation air dry (water −0.4 < −100 MPa). The senses dew point vapor with miniature cooled mirror located above sample closed chamber. Readings for individual samples are obtained rapidly (2–5 min). Accuracy measurement checked periodically using...

Particle‐size distributions (PSDs) of soils are often used to estimate other soil properties, such as moisture characteristics and hydraulic conductivities. Prediction properties from texture requires an accurate characterization PSDs. The objective this study was test the validity a mass‐based fragmentation model describe PSDs in soils. Wet sieving, pipette, light‐diffraction techniques were obtain 19 range 0.05 2000 μm. Light diffraction allows determination smaller particle sizes than...

Abstract A heat flow theory has been developed which can be used to predict freezing and thawing cycles of a temperate soil. The latent fusion is incorporated into the classical equation with capacity thermal conductivity soil modified include terms account for phase transformation. Computations Palouse silt loam show that ice‐liquid transformation occurs over defined temperature range where apparent may take on values are several orders magnitude larger than those either in unfrozen or near...