Unsaturated Conductivity Research Articles

Effect of Daily Irrigation on Water Content and Suetion Profiles in Soils of Three Textures

AbstractA growth‐room study was conducted to evaluate the water and suction profiles that develop in various soils irrigated daily at different proportions of Et. When irrigated to just replace Et, the water profiles that developed depended upon the flow characteristics of the soil. In the soil in which water moved readily (Shano silt loam), water distribution was nearly uniform with depth and did not change with time. In the soils in which water moved slowly, either because of slow internal water movement when wet (Ritzville loam) or low unsaturated conductivities at relatively low suctions (Sagehill sand), the upper soil became wetter while the lower soil water decreased by a corresponding amount. In all soils irrigated daily to replace all or more than Et, suctions in the upper soil were relatively low. With the soil profile initially wet, several weeks of deficit irrigation passed before surface soil water content changed markedly.

Use of Pressure Bomb Measurements to Estimate Root Water Potentials1

AbstractPressure bomb measurements were used to estimate root water potentials of soil‐grown pepper (Capsicum annum L. cv. ‘California Wonder’) plants. Bomb measurements taken on roots of wilted pepper plants in dry soil overestimated the water potential by as much as 8 bars when roots were known to be damaged. When plants were equilibrated at low water potentials (‐10 to ‐14 bars) and the roots were undisturbed, differences between water potentials in the plant roots and top were 0.4 bars or less.Increases in water potential with time were observed in both stressed and well‐watered plants where roots were not damaged but where there was no attempt to equilibrate the water potential gradient. Root resistance, root pressure and unsaturated conductivity of the soil all influence the tune dependence of root water potential.

Comparison of measured and calculated hydraulic conductivities of unsaturated soils

Three methods to calculate the unsaturated conductivity of soil from its moisture characteristic were tested. Calculated values were compared with direct measurements of conductivity for both sorption and desorption for a sand. Also, comparisons were made for three soil materials. The method of calculation proposed by Millington and Quirk [1959], when matched at the saturated conductivity, gave good results.

Moisture Retention by Soil with Coarse Layers in the Profile

AbstractThe effects of coarse strata on the moisture retention characteristics of soil profiles were evaluated. A sandy loam soil was underlain at various depths by sand or gravel and the moisture status of the soil was observed for 2 months following a heavy irrigation.The moisture retained by soil underlain by sand or gravel was much greater than in similar depths of a uniform soil. The moisture content of the soil above a layer increased as the layer was approached. The moisture content of the soil underlain by sand or gravel changed very little after the first few days following irrigation whereas in the uniform soil moisture moved downward throughout the observation period.The moisture retention characteristics of the profiles were roughly estimated from laboratory measurements of unsaturated conductivities of the sand and gravel and from a moisture characteristic curve of the soil.