Abstract. Conventional models of liquid distribution, flow, and solute transport in partially saturated porous media are limited by the representation of media pore space as a bundle of cylindrical capillaries (BCC). Moreover, the capillary model ignores the dominant contribution of adsorptive surface forces and liquid films at low potentials. We propose two new complementary elements for improving our understanding of liquid configuration in porous media: (1) an approach for considering the individual contributions of adsorptive and capillary forces to the matric potential and (2) a more realistic model for pore space geometry. Modern interface science formalism is applied to determine the thickness of adsorbed liquid films as a function of thermodynamic conditions and specific surface area of the medium. The augmented Young-Laplace (AYL) equation provided the necessary framework for combining adsorptive and capillary processes. A new pore space geometry composed of an angular pore cross section (for capillary processes) connected to slit-shaped spaces with internal surface area (for adsorption processes) offers a more realistic representation of natural porous media with explicit consideration of surface area (absent in the standard BCC model). Liquid-vapor configuration, saturation, and liquid-vapor interfacial area were calculated for different potentials and pore (unit cell) dimensions. Pore dimensions may be easily related to measurable soil properties such as specific surface area and porosity. Rigorous calculations based on the AYL equation were simplified and led to the development of algebraic expressions relating saturation and interfacial area of liquid in the proposed pore space geometry to chemical potential. These simple expressions are amenable to upscaling procedures similar to those presently used with the BCC model.

Studies of crop response to water and salt stress vary either salinity with a high leaching fraction or irrigation in the absence of salinity to isolate and quantify the effects of the two types of stress. Under deficit irrigation with saline water, a water conserving practice, the crop experiences simultaneous matric and osmotic stress, and it is not known if experiments designed to isolate stress effects may be used to predict crop response to simultaneous stresses. Thus, a study was conducted wherein yields were determined under varying levels of salinity and irrigation. Corn (Zea mays L.) and melon (Cucumis melo L.) were grown at the Arava Research and Development Farm in Yotvata, Israel, and alfalfa (Medicago sativa L.) at the Utah Power & Light Research Farm in Huntington, UT. Corn and melon plots were drip irrigated at six ratios of potential evapotranspiration ranging from 0.2 to1.7 in combination with four salinity levels. Alfalfa was irrigated with water of 0.2 and 4.0 dS m−1 from a line‐source sprinkler. For all three crops, the salinity treatments consisted of a control treatment with a salinity level less than published salt‐tolerance thresholds. Interactive effects of salinity and water stress were not observed in these field experiments. At low irrigation levels (≈70% of potential evaporation), yields were unaffected by the salinity level. At the higher irrigation levels, the salinity level caused significant differences in yield. Yield data were fit to piecewise linear models that emphasized the limiting nature of the effects of salt and water stress.

[1] An accessible solution capable of reliably predicting plant-environmental interrelationships for variable species, climates, soils, and management options is a necessary tool for creating sustainable agriculture and environmental preservation. A mechanism-based analytical solution, the first of its kind that considers multiple environmental variables and their combined effects on plant response, was developed and tested. Water uptake by plants, water and salt leakage below the roots, and yield are calculated by solving for transpiration in a single mathematical expression according to limitations imposed by root zone salinity and water status. Input variables include the quantity and salinity of applied water, terms for plant sensitivity to salinity and to water stress, potential evapotranspiration, and soil hydraulic parameters. Where water was not limiting, regression of predicted versus measured data resulted in r 2 = 0.96 with slope of 0.937 and intercept of 0.033 (not different from 1 and 0 at 99% confidence), where irrigation varied and salinity was not limiting the r 2 = 0.94 with slope of 0.906 and intercept of 0.044 (not different from 1 and 0 at 99% confidence), where both salinity and water levels varied r 2 = 0.94 with slope of 0.966 and intercept of 0.033 (not different from 1 and 0 at 99% confidence). Application of the model for agricultural and environmental management and economic analysis is discussed. For example, a farmer in the Arava in Israel where irrigation water salinity is high (electrical conductivity of 3 dS m À1 ) cannot expect to reach greater than 70% of the potential yield for a pepper crop with any amount of irrigation. By choosing melon, the farmer can achieve 90% of potential yield with the same quality and quantity of water.Citation: Shani, U., A. Ben-Gal, E. Tripler, and L. M. Dudley (2007), Plant response to the soil environment: An analytical model integrating yield, water, soil type, and salinity, Water Resour. Res., 43, W08418,

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crested wheatgrass [Agropyron cristatum (L.) Gaertn.] (Dewey, 1960(Dewey, , 1962. A lack of salt-tolerant cultivars may be due in part to inadequateEven though the literature contains numerous reports evaluation protocols used for selection. Our objective was to develop indicating variability for tolerance to salinity in many a greenhouse protocol that is simple and consistently separates genocrops, few salt-tolerant cultivars have been released (Flowtypes for their relative ability to survive under saline conditions. In 2000 and 2001, 12 alfalfa (Medicago sativa L.) cultivars were seeded ers and Yeo, 1995). Sruvastave and Jana (1984) and Shanin 3.8-by 21-cm cone-shaped containers plugged with capillary matting non (1984) attribute the lack of salt-tolerant cultivars and filled with silica sand. Six-week-old seedlings were submersed in to multiple factors, including inadequate means of dea NaCl-nutrient solution starting at an electrical conductivity (EC) tecting and measuring plant response to salinity and of 3.0 dS m Ϫ1 and increased 3.0 dS m Ϫ1 every 1 to 2 wk for 10 to 13 ineffective selection methods. Selection of salt-tolerant wk. Probit analysis was used to estimate the time and salt dose to plants from saline fields or plots seems a logical step reach 50 (LD 50 ) and 75% (LD 75 ) mortality. Probit results were comfor most plant breeders; however, this procedure has pared with cultivar ranking for mean percentage plant mortality when not produced consistent results (Shannon, 1984). Selecoverall trial mortality reached approximately 50 and 75%. Pearson's tion in the field is not efficient because soil salinity rank correlations between 2000 and 2001 at the LD 50 and LD 75 levels varies substantially with time, location, soil type, and were r ϭ 0.90 (P Ͻ 0.001) and r ϭ 0.88 (P Ͻ 0.001), respectively. Rank correlations between 2000 and 2001 based on means whendepth. Furthermore, it has been reported that little relaoverall trial mortality levels were approximately 50 and 75% were