Papers by Victor A Snyder Sevits
Soil Science Society of America Journal, 1987
The physics of soil deformation under applied external loads is still very poorly understood. Thi... more The physics of soil deformation under applied external loads is still very poorly understood. This is especially true in the case of unsaturated soils, where very complex internal force systems arise as a result of applied loads, stresses in the pore fluid phases, and surface tension forces in the air‐water interface. The present paper attempts a theoretical description of these forces, for the relatively simple case of nonswelling cohesionless granular soils in static equilibrium. The analysis concentrates on systems which are similar according to the rules defined by Miller and Miller (1956) in their theory of capillary flow phenomena in granular media. Applied loads, gravity, and stresses in the pore fluid phases are analyzed in terms of their effects on the interparticle contact forces which determine soil behavior. For isotropic similar media under similar applied loads, interparticle contact forces can be approximated as linear combinations of the scalar groups (σ̄‐µa) λ21, ρg...
Soil Science Society of America Journal, 1985
Hydrology
The authors wish to make the following corrections to this paper (V [...]
The Journal of Agriculture of the University of Puerto Rico
Drought mortality of juvenile trees is a major cause for failure ofreforestation projects. Portab... more Drought mortality of juvenile trees is a major cause for failure ofreforestation projects. Portable devices such as passive radiative dew condensers can often provide 0.15 L/day of water in situ, possibly sufficient for tree survival until roots can access groundwater, allowingself-sustainability. To evaluate growth and survivability of juvenile trees of Tabebuia heterophylla Britton and Swietenia macrophylla King under suchlow water amounts, juvenile trees received approximately 0.033, 0.067, 0.134, 0.201 and 0.268 L/tree/day, representing fractions (relative evapotranspirationor RET) of 0.125, 0.25, 0.50, 0.75 and 1.00 of the evapotranspiration demand (ETo). The experiment lasted 60 days for S. macrophylla and 90 days for T. heterophylla. All T. heterophylla juvenile trees survived even at the lowestirrigation rate. However, S. macrophylla juvenile trees began dying at RET < 0.5, with only 60 percent surviving at RET = 0.25 (0.067 L/day) and 100 percentmortality occurring at RE...
The Journal of Agriculture of the University of Puerto Rico
COMPARISON OF THE CASAGRANDE AND DROP-CONE PENETROMETER METHODS FOR MEASURING THE LIQUID LIMIT IN... more COMPARISON OF THE CASAGRANDE AND DROP-CONE PENETROMETER METHODS FOR MEASURING THE LIQUID LIMIT IN PUERTO RICAN SOILS
Dew condensers have been proposed as a means to reduce drought mortality of tree seedlings i... more Dew condensers have been proposed as a means to reduce drought mortality of tree seedlings in early stages of reforestation projects. We investigated the amount of dew condensate produced by locally constructed dew condensers, constructed with three different infrared emitting surfaces: standard polyethylene/ TiO2 / BaSO4 foil, thermoplastic polyolefin (TPO), and plastic coated with locally available Lanco UrethanizerTM8 roofing paint. All surfaces produced similar amounts of total dew condensate, typically ranging between 0.05 and 0.25 L/m2/night. However, the materials differed in the fraction of dew running off the surfaces, which represents the water available for tree seedlings. Highest runoff fractions were obtained with painted surfaces, followed by polyethylene and polyolefin surfaces, respectively. Considerably greater amounts of nightly dew condensate were observed during the winter than in summer, attributed to d...
Hydrology, 2022
A phenomenon causing instability of soil structure and associated hydraulic properties in recentl... more A phenomenon causing instability of soil structure and associated hydraulic properties in recently tilled soils is aggregate fragmentation induced by wetting and drying cycles. We analyzed data from three experiments in Puerto Rico, the UK and China measuring fragmentation and resulting evolution of aggregate size distributions during successive wetting and drying cycles in heavy textured soils. Aggregate distributions were represented as the cumulative fraction F of aggregates passing through successively larger sieve sizes X. To a good approximation, all distributions exhibited similarity in that the aggregate diameter X(F) corresponding to F in a given test distribution was always a characteristic multiple α¯ of X(F) in a fixed reference distribution, where α¯ for a distribution was calculated as its mean weight aggregate diameter (MWD) divided by the MWD of the reference distribution. In most cases, α¯ for a given soil varied inversely with the square of the number of wetting an...
Tillage modifies soil structure, altering conditions for plant growth and transport processes thr... more Tillage modifies soil structure, altering conditions for plant growth and transport processes through the soil. However, the resulting loose structure is unstable and susceptible to collapse due to aggregate fragmentation during wetting and drying cycles, and coalescense of moist aggregates by internal capillary forces and external compactive stresses. Presently, limited understanding of these complex processes often leads to consideration of the soil plow layer as a static porous medium. With the purpose of filling some of this knowledge gap, the objectives of this Project were to: 1) Identify and quantify the major factors causing breakdown of primary soil fragments produced by tillage into smaller secondary fragments; 2) Identify and quantify the. physical processes involved in the coalescence of primary and secondary fragments and surfaces of weakness; 3) Measure temporal changes in pore-size distributions and hydraulic properties of reconstructed aggregate beds as a function of...
The Journal of Agriculture of the University of Puerto Rico, 1969
A study was conducted in a commercial drip irrigated tomato (var. Floradel) field to investigate ... more A study was conducted in a commercial drip irrigated tomato (var. Floradel) field to investigate fertilizer solute movement patterns in relation to dripper location. Six tomato plots were established, three of which were planted and the other three left fallow. Soil samples were taken at planting and after harvest at various locations from the dripper and were analyzed for electrical conductivity, pH, bicarbonate-extractable P, and ammonium acetate-extractable (IN, pH 7), K, Na, Ca, and Mg. All fertilizer was applied via drip irrigation. Considerable movement of P was observed throughout the soil profile possibly because of slow rates of calcium phosphate precipitation due to the low pH of the irrigation water and the possible presence of Mg+2 and HCO3-1 in solution, and to the predominant movement of fertilizer solutions through soil macropores. Movement of K was less evident than that of P, but could have been masked by large plant uptake of K. Increases in electrical conductivity...
The Journal of Agriculture of the University of Puerto Rico, 1969
This study evaluated interactive effects of mineralogy and organic matter content on chemical and... more This study evaluated interactive effects of mineralogy and organic matter content on chemical and physical properties of clay soils. Measurements were taken at different depths in four soil profiles characterized by oxidic, kaolinitic, mixed and montmorillonitic clay mineralogies, respectively. Within a given profile, organic carbon content varied more or less continuously with depth, whereas texture and mineralogy remained relatively constant. Thus in this study the combined effects of organic matter content and clay mineralogy could be evaluated in various combinations while texture remained constant. Resistance of soil aggregates to slaking by water was related primarily to soil organic matter content, with relatively minor differences attributable to mineralogy except in the oxidic soil where oxides seemed to exert an important stabilizing effect. Organic matter was associated with an increase in water-holding capacity both in the interaggregate pore space (0 to -0.33 bar moistu...
The Journal of Agriculture of the University of Puerto Rico, 1969
Magnesium deficiency is a major constraint for banana and plantain (Musa spp.) production in high... more Magnesium deficiency is a major constraint for banana and plantain (Musa spp.) production in highly weathered soils. A study was conducted on an Ultisol (Aquic Haplohumult) of the central mountainous region of Puerto Rico to evaluate the effect of several factors on magnesium availability to plantain. Four target levels of soil exchangeable Mg:K ratios: 0.6, 2.0, 4.0 and 8.0; two lime application treatments: no lime, limed to pH 5.5; and two fertilization programs were evaluated in a split-split plot experimental design. Results indicated a highly positive correlation between soil magnesium levels and crop performance. Significant effects were observed on days to flowering, plant height, number of leaves at flowering, leaf magnesium content, and yield. A 25% yield increase was observed at the lowest magnesium increment relative to the control. In addition, the ratio of nonbearing plants per experimental plot was reduced with increments in soil magnesium. It was calculated that in th...
The Journal of Agriculture of the University of Puerto Rico, 2018
Dew condensers have been proposed as a means to reduce drought mortality of tree seedlings in ear... more Dew condensers have been proposed as a means to reduce drought mortality of tree seedlings in early stages of reforestation projects. We investigated the amount of dew condensate produced by locally constructed dew condensers, constructed with three different infrared emitting surfaces: standard polyethylene/ TiO2 / BaSO4 foil, thermoplastic polyolefin (TPO), and plastic coated with locally available Lanco UrethanizerTM8 roofing paint. All surfaces produced similar amounts of total dew condensate, typically ranging between 0.05 and 0.25 L/m2/night. However, the materials differed in the fraction of dew running off the surfaces, which represents the water available for tree seedlings. Highest runoff fractions were obtained with painted surfaces, followed by polyethylene and polyolefin surfaces, respectively. Considerably greater amounts of nightly dew condensate were observed during the winter than in summer, attributed to differences in night length and cloud cover. A commercially a...
Soil Science Society of America Journal, 1997
A longstanding problem in the thermodynamic theory of ion exchange has been lack of a general met... more A longstanding problem in the thermodynamic theory of ion exchange has been lack of a general method for measuring activities of solid‐ion complexes or exchanger species. Existing theory, based on integrating the Gibbs‐Duhem relation for a solid exchanger phase immersed in an electrolyte solution, is often subject to uncertainties due to indeterminate amounts of solvent and electrolytes adsorbed onto the exchanger surface. We remove these difficulties by treating ion exchange systems as simple mixtures of solvent, electrolytes, and exchanger species, with no formal partitioning into phases. Through judicious choice of components, an integrable Gibbs‐Duhem relation is obtained that can be solved for the activity of any arbitrary exchanger species, requiring only reversibility of the system and measurable solvent and electrolyte activities. The theory is very general in principle and is applicable to variable‐ and permanent‐charge solid exchangers with positive and negative surface ch...
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Papers by Victor A Snyder Sevits