Rapid drought resistance screening techniques could accelerate selection of improved cultivars for semiarid areas. This study was conducted to determine if total leaf water potential, leaf relative water content, and leaf diffusive resistance could be used to differentiate between barley (Hordeum vulgare L.) cultivars differing in apparent drought resistance. Resistant and susceptible cultivars were selected by regressing individual cultivar yields against site mean yield for numerous yield trials. Individual plants were grown in cone-tainers (plastic tubes 25 mm in diameter and 123 mm long). The lower 30 mm of the cone-tainers were imbedded in sand so that roots emerging from the bottom of the cone-tainers were in the capillary fringe above a water table in the sand. Fifty plants were grown at a time in a sand bed, five replications each of five resistant and five susceptible barley cultivars of either two-or six-row head types. At the three-leaf growth stage total leaf water potential (.J;,) was measured on the third leaf of each plant under low stress conditions (predawn). Water was then drained from the sand bed to stress the plants. Leaf diffusive resistance (LDR) was measured at 1000 and 1300 h each day as stress developed. When the PM diffusive resistance reached about 1000 s m-•, relative water content (RWC) of the second leaf was determined. All measurements were repeated in three different trials for each head type. Relative water content and .J;, differentiated between drought-resistant and drought-susceptible groups of twoand six-rowed barley at the 0.01 probability level in every trial. Leaf diffusive resistance differentiated between resistant and susceptible groups at the 0.01 or 0.05 level under low and high stress conditions. Neither RWC nor LDR allowed separation of cultivars within resistant or susceptible groups, but .J;, did show differences between cultivars within groups. These techniques provide an easy method to screen for drought-resistant barley.

Little evidence is documented regarding the effects of timber‐harvest traffic on volcanic‐ash‐mantled glacial till soils and clay‐rich Tertiary volcanic‐derived soils of northwestern Montana. We identified and characterized differences in the soil physical properties between trafficked and nontrafficked areas. Soil‐clod bulk density, infiltration, and soil‐clod water retention were measured on 54 pedons from nontrafficked and moderately and severely trafficked sites. Soil mechanical properties were characterized using 18 nontrafficked pedons. Compared with nontrafficked areas, bulk densities in severely trafficked areas at the 15‐cm depth were 76, 21, and 21% greater in ash over limestone till, ash over quartzite till, and Tertiary volcanic soils, respectively. Water retention at 0.002, 0.010, and 0.033 MPa was significantly lower at the 15‐cm depth in trafficked than in nontrafficked areas of ash over limestone till. Similar differences were observed in ash over quartzite till. Compared with nontrafficked areas, cumulative 1‐h infiltration in severely trafficked areas was 81% less in ash over limestone till, 79% less in ash over quartzite till, and 87% less in Tertiary volcanic soils. Similar but smaller differences were detected in moderately trafficked areas. Three independent measurements demonstrated significant differences in surface horizon physical properties between trafficked and nontrafficked areas. We detected significant physical manifestations of traffic‐induced soil compaction below 30 cm.

Canopy temperature under a set of environmental conditions is an integrated result of the energy absorption and dissipation mechanisms acting within the canopy. The relative magnitude of these various mechanisms may affect the amount and efficiency of water use. We studied the influence of different morphological features such as plant color, awn length, and waxiness on canopy temperatures of field grown barley (Hordeum vulgare L.). Morphological differences were obtained by using barley lines isogenic for the various features. Canopy temperatures were measured with an infrared thermometer on five different dates within a 21‐day period after heading. Light‐colored plants were significantly cooler (5% level) than normal‐colored plants. Awn length significantly (5% level) affected canopy temperatures of a sixrow variety; awned canopies were cooler than awnless. Awn length did not affect the canopy temperatures of a two‐row variety. Waxiness did not affect canopy temperatures. Calculations indicate that differences in canopy temperatures due to plant morphology could significantly affect water use.

A method of using gamma-ray absorption to measure the moisture content of a small volume of soil is described. The method appears promising in the study of unsaturated water flow, provided that the soil does not swell as water is applied, since measurements of both bulk density and water content can be obtained without disturbing the system. Water contents in a volume of soil about 1 cm. wide were measured to an accuracy of about ±0.5% by volume.

Soil water and temperature distributions in a silty clay loam soil were studied in the field under freezing winter conditions. Appreciable upward water movement to a frozen zone occurred in plots in which the unfrozen subsoil water was held at tensions of less than about 2 atm. and water held at tensions of less than 5 atm. moved toward the frozen zone. It appears that the upward water movement to the frozen zone conributed to overwinter water losses since soil water losses of 0.36 and 0.50 inches were measured from those plots in which there was appreciable upward water movement. Plots containing 7.9, 6.2, 4.2, and 1.4 inches of available water before freezing occurred conserved −0.36, −0.50, 0.0, and 0.81 inches, respectively, of the 4 inches of precipitation that occurred during the winter.