# Bulk density and porosity relationship

### WM Earthcare » Everyday Soil Science #4: Bulk Density & Porosity

Article shared by: After reading this article you will learn about the relationship between porosity and density of soil. % soil space = bulk density/particle density. The bulk density values ranged from to and the porosity from to Keywords: bulk density, correlation coefficient, micro-structures, porosity, . Table 1: The relationship between compaction, apparent density and porosity. Degree of. Apparent. Total. Macro. Micro. Compaction. Density. Porosity. Porosity .

Aggregation involves particulate adhesion and higher resistance to compaction. Typical bulk density of sandy soil is between 1. This calculates to a porosity between 0. Typical bulk density of clay soil is between 1.

### Practice problems: Porosity and bulk density

This seems counterintuitive because clay soils are termed heavy, implying lower porosity. Heavy apparently refers to a gravitational moisture content effect in combination with terminology that harkens back to the relative force required to pull a tillage implement through the clayey soil at field moisture content as compared to sand. Porosity of subsurface soil is lower than in surface soil due to compaction by gravity.

Porosity in finer material below the aggregating influence of pedogenesis can be expected to approximate this value. Soil porosity is complex.

Traditional models regard porosity as continuous. This fails to account for anomalous features and produces only approximate results. Furthermore, it cannot help model the influence of environmental factors which affect pore geometry.

A number of more complex models have been proposed, including fractalsbubble theory, cracking theory, Boolean grain process, packed sphere, and numerous other models. The characterisation of pore space in soil is an associated concept. Types of geologic porosities[ edit ] Primary porosity The main or original porosity system in a rock or unconfined alluvial deposit.

Secondary porosity A subsequent or separate porosity system in a rock, often enhancing overall porosity of a rock. This can be a result of chemical leaching of minerals or the generation of a fracture system. Particle density varies little between minerals and has little practical significance except in the calculation of pore space.

Porosity is that portion of the soil volume occupied by pore spaces. This property does not have to be measured directly since it can be calculated using values determined for bulk density and particle density. A cm3 cylindrical container was used to collect an undisturbed soil sample.

AGPR201 08 02 Bulk Density

The container and soil weighed g when dried. When empty the container weighed 75 g. What is the bulk density and porosity of the soil? To determine bulk density: Bulk Density Sampling Note: You will be sharing your bulk density, porosity, and field texture results with the rest of the class. Please put your results on the board when you have completed the calculations. These values are needed for some of the questions at the end of the lab.

Choose sampling sites from several locations at least three and hypothesize about the differences in bulk density you expect to find and WHY. Never till or operate equipment when soils are wet. Utilize mulch, plant stubble, compost, and green manure cover crops to displace the weight of people and equipment on the soil surface.

Always keep soil covered, even during short-term work activities.

Use a diversity of plant materials deep rooted as well as shallow rooted to break up compacted soil layers. Aerate turf and planted areas twice annually using a tine-type aeration device. Implementing the practices above will go a long way to keeping the bulk density of your soil more like a sponge rather than a brick.

And who plants in a brick…? For more information about bulk density and soil porosity contact your local Master Gardener office, or click here to download an educational factsheet from the USDA, Natural Resources Conservation Service.