D. HILLEL’s research while affiliated with University of Massachusetts Amherst and other places

This book is a unified, condensed, and simplified version of the recently issued twin volumes, Fundamentals of Soil Physics and Applications of Soil Physics. Nonessential topics and complexities have been deleted, and little prior knowledge of the subject is assumed. An effort has been made to provide an elementary, readable, and self-sustaining description of the soils physical properties and of the manner in which these properties govern the processes taking place in the field. Consideration is given to the ways in which the soils processes can be influenced, for better or for worse, by man. Sample problems are provided in an attempt to illustrate how the abstract principles embodied in mathematical equations can be applied in practice. The author hope that the present version will be more accessible to students than its precursors and that it might serve to arouse their interest in the vital science of soil physics.

An abridged, student-oriented edition of Hillel's earlier published Environmental Soil Physics, this is a more succinct elucidation of the physical principles and processes governing the behavior of soil and the vital role it plays in both natural and managed ecosystems. The textbook is self-contained and self-explanatory, with numerous illustrations and sample problems. Based on sound fundamental theory, the textbook leads to a practical consideration of soil as a living system in nature and illustrates the influences of human activity upon soil structure and function. Students, as well as other readers, will better understand the importance of soils and the pivotal possition they occupy with respect to careful and knowledgeable conservation.

Three methods for assessing soil hydraulic properties were conducted and their results compared for two soils in Western Massachusetts. The methods compared are: the Instantaneous Profile Method, the Guelph Permeameter, and laboratory determination using intact soil cores. The saturated hydraulic conductivity and unsaturated conductivity function, as well as the moisture retention relationship when possible, were determined and the results compared with respect to their ranges of applicability and the respective limitations of each method. We found close agreement for the moisture retention relationships determined by the instantaneous profile method and the soil cores for the ranges of pressures and moisture contents they have in common. In addition, there was also close agreement between the K([PHI]) relationship measured using the instantaneous profile method and that predicted using the van Genuchten and Mualem models. The field saturated conductivity results determined using the Guelph Permeameter were one to three orders of magnitude less than the saturated conductivity results determined from soil cores and those determined by the instantaneous profile method. The unsaturated K([PHI]) relationship using Gardner's definition of matric potential and the results from the Guelph permeameter predicted hydraulic conductivity values three to four orders of magnitude less then the other two methods at 200 cm of pressure. (C) Williams & Wilkins 1993. All Rights Reserved.

We used a simulation model based on the matric flux potential concept to describe two-dimensional infiltration from a line source. The model showed considerable stability with varying compartment sizes and trickle discharges. The simulated wetting patterns indicated closer agreement with published experimental data than did alternative models, especially under high rates of trickle discharge. (C) Williams & Wilkins 1984. All Rights Reserved.

Water desorption and mercury intrusion methods were used to characterize the pore size distribution of a sand, and the hydraulic conductivity-water content function, K(o), was calculated therefrom. When used as input to an infiltration simulation model, the K(o) function obtained from the water desorption method resulted in a better prediction of the actual wetting profiles than did the K(o) from mercury intrusion. However, the results of the latter method could be made to match those of the former by use of an empirical correction factor. It appears, therefore, that the mercury intrusion method, which offers the advantage of rapidity, can be helpful in characterizing soil hydraulic behavior only if its results are appropriately adjusted.

This book is not, in any case, in total defiance of the Wise Old Mans admonition, for it is not an entirely new book. Rather, it is an outgrowth of a previous treatise, written a decade ago, entitled "Soil and Water: Physical Principles and Processes." Though that book was well enough received at the time, the passage of the years has inevitably made it necessary to either revise and update the same book, or to supplant it with a fresh approach in the form of a new book which might incorporate still-pertient aspects of its predecessor without necessarily being limited to the older books format or point of view.

The validities of different K(θ) relations obtained from five experimental techniques and three numerical methods were evaluated using experimental data of vertical infiltration for the same soil. The different K(θ) relations were used in a simulation model of vertical infiltration assuming a constant rate of water application lower than the saturated hydraulic conductivity. The simulated data of moisture contents and depths of wetting fronts were compared with the experimental measurements. Among the experimental methods for the K(θ) relation, the instantaneous profile method (IPM) resulted in the best description of the infiltration profile for the sand used in this study. Among the numerical methods of K(θ) estimation, Irmay’s model compared favorably with Jackson’s (p = 1) and Mualem’s (x = 0.5) approaches. The prediction of the Jackson model could be improved by setting p equal to 0.5 instead of 1. We conclude that numerical methods of estimating the K(θ) function can be substituted for the experimental methods only if great care is taken in choosing the proper physical parameters for the soil under consideration.

We compared experimentally measured hydraulic conductivity-water content relationships with those predicted by three models. Sand was the medium used for this comparative study. The laboratory methods used included: instantaneous profile-internal drainge; infiltration through crust; hot air drying; pressure plate outflow; and unit gradient drainage. For the numerical approach, we used the Irmay, the Jackson, and the Mualem models. The moisture desorption curve and the saturated hydraulic conductivity were used as inputs. Additional parameters were estimated from the literature. We found close agreement between the K([theta]) relationship measured according to the instantaneous profile method and estimates based on Irmay's equation; Jackson's prediction method, with a pore interaction exponent of 0.5; and Mualem's model, with an effective saturation term exponent of 0.5. In addition, the predicted K([theta]) relationship with the Mualem model, using 0.75 as exponent of the effective saturation term, and the predicted values with the Millington and Quirk equation (being Jackson's model with p = 4/3), corresponded with the experimental relationship obtained by the gypsum-sand crust technique. The predicted K([theta]) relationships obtained by the above models also matched the K([theta]) values obtained by the hot air method in the wet range. (C) Williams & Wilkins 1981. All Rights Reserved.

We conducted a combined simulation-experimentation study to monitor the simultaneously changing states of plant water and of soil water during a period of continuous transpiration by uniformly rooted ryegrass, grown in pots filled with a sandy soil, under two levels of evaporative demand. The pattern of soil moisture extraction was measured by weighing and tensiometry, and that of plant water potential, by leaf psychrometry. A macroscopic-scale extraction model, previously published by the authors, was modified to account for the water-storage characteristics of the crop. Both the original and the modified versions of the model were found able to provide a realistic description of the diurnal fluctuations of plant water potential during the period prior to the onset of plant water stress, but they were less realistic in describing the decline of plant water potential during the dehydration and wilting phases. The rehydration of the crop from a stressed condition could be simulated realistically only by assigning a higher value of root resistance than during the initial extraction phase. (C) Williams & Wilkins 1980. All Rights Reserved.