Weight-Volume Relationships 3 (original) (raw)

An Example Emphasizing Mass–Volume Relationships for Problem Solving in Soils

Journal of Natural Resources and Life Sciences Education, 2009

B oth undergraduate and graduate courses dealing with soil physical properties typically begin with descriptions of basic mass-volume relationships among phases of the soil system. Soil particle density, bulk density, water content, porosity, texture, and other soil physical properties are defined according to mass-volume relationships. Schematic diagrams in which each soil component phase (air, water, solid, etc.) is shown separately provide a tool for visualization of the components of the soil system and definition of soil physical properties (Fig. 1). These diagrams have been incorporated, to a limited extent, into many textbooks on soil science and soil physics as a descriptive or illustrative tool in various forms (e.g., Brady and Weil, 2000; Hillel, 2004; Jury and Horton, 2004). Although these diagrams are a valuable tool for property definition, their use as a problem-solving tool should also be emphasized. Engineering texts have expanded the use of mass-volume diagrams by implementing them as tools to solve phase problems. Schematic diagrams provide a means for quantitative comparison of two or more soil systems as well as for systematic calculation of changes in a given soil system. Ability to utilize mass-volume relationships and schematic diagrams for problem solving strengthens the potential for communication between individuals with soils backgrounds and those in other geo-science and engineering disciplines where quantitative problem solving tends to be a routine curriculum component. Our objective for this article is to outline a practical, applied problem-solving exercise using mass-volume relationships and schematic diagrams that can be adapted as a classroom example, group problem-solving activity, or classroom assignment. The example is developed from Ewing and Vepraskas (2006) where mass-volume relationships were used to determine subsidence in an organic Carolina Bay soil. We begin with the problem description, continue with assumptions necessary for developing the solution, and finally present steps that can be followed to solve the problem based on mass-volume relationships. We conclude the first two sections with questions that can be posed to facilitate student reasoning toward the problem solution. Potential adaptations are included in the discussion.

Soil and Soil Water Relationships

2016

This publication presents and discusses concepts that are fundamental to understanding soil, water, and plant relationships and the soil water balance. Knowledge about soil water relationships can inform the decision-making process in agricultural operations or natural resource management, such as determining what crops to plant, when to plant them, and when various management practices should be scheduled. Understanding these concepts is useful for addressing both agronomic and policy issues related to agricultural water management. Soil Soil Composition and Texture Soils are composed of four components: mineral solids, organic matter solids, water, and air. The solids are made of minerals derived from geologic weathering and organic matter consisting of plant or animal residue as well as living organisms. The empty spaces between the solids, called pores, are occupied by either water or air. The mineral solid fraction of the soil is made up of sand, silt, and clay, the particular ratios of which determine the soil texture. Sand particles range in size from 0.05 to 2.00 mm, silt ranges from 0.002 to 0.050 mm, and the clay fraction is made up of particles smaller than 0.002 mm in diameter. Particles larger than 2.0 mm are referred to as rock fragments and are not considered in determining soil texture, although they can influence both soil structure and soil water relationships. Once the sand, silt, and clay fractions are known, the textural class can be determined using a soil textural triangle (fig. 1). Most land-grant universities and private labs can determine the sand, silt, and clay fractions of soil samples. Soil texture determination is important because many soil properties are influenced by texture, including drainage, water-holding capacity, aeration, susceptibility to erosion, cation exchange capacity, pH buffering capacity, and soil tilth. Figure 1. U.S. Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) soil textural triangle showing how to determine the soil texture from the percentages of sand, silt, and clay. The soil used as an example here is a loam composed of 40 percent sand, 45 percent silt, and 15 percent clay.