Module 10: Soil Density

What is density

Density is a fundamental physics measurement, it is a measure of the relative amount of pores and solid particles. The few were pours there are per unit volume, the higher is the density. It is the mass of an object divided by its volume For some materials such as water the density changes with other factors like temperature

Particle Density

Particle density is a measure of the density of the solid particles themselves and is determined by dividing the dry weight of soil particles by the volume of those particles.

High bulk density soil effects

Plant roots, organisms, water movement

Core method

An intact core sample is dried at 105°C until it reaches is a constant weight Weight of dry core is then divided by its volume which yields both density. Pros: easy to perform, cons: severely affected by rocks

Gamer scattering probe

Bulk density is calculated based on the amount of signal that bounces back to the detector. More signal reflected equals higher density, Less signal reflected equals lower density

Measuring soil bulk density

Coors, clods, radiation

Range of bulk density is found in soil's

Low: 0.8-1.1g/cm3 Soil is very high in organic matter, Histosols, and some soil derived from volcanic ash, Andisols. Normal: 1.1-1.5g/cm3 Most Upland minerals soil's fault in this range and values are influenced by texture and structure High: >1.5g/cm3 Bulk density is in this range are usually caused by artificial compaction or well graded material

Soil bulk density and texture

Since clay particles are much smaller than sand particles, for a given volume of soil there is more pore space in clays soil's as compared to sand. If the soil were completely dry the poor space would be filled with weight loss error in the clay soil would be less dense. Poorly graded material has a uniform particle size distribution compared to a well graded material which has soil particles from a number of different size classes. And well graded material, large pores are filled with large size particles, medium pores are filled with medium sized particles and small pores are filled with small size particles, resulting in a much denser material

Wrap up

Soil bulk density is a very important physical property of soil The normal range of bulk density for soils is between 1.1 and 1.5 g/cm3 and is affected by soil texture Soils bulk density can affect many different aspects of the soil's functionality, such as plant roof penetration, earthworm activity, and water movement There are three common method is used to determine the soil bulk density: Poor, Clod and radiation

Bulk density

Soil bulk density is determined by dividing the weight of Solids and air by the volume of solids and air. Soil water not included in the calculation

Clod method

Soil clogged taken from pit clots then coded with wax or liquid saran, coded clot is then wait an hour and then weighed in a liquid of known density to get its volume. A sub sample was taken to determine the water content, both density is then calculated by mass of the dry soil divided by its volume. Cons: labor-intensive

Why is bulk density important

Soil is a three phase system Air Water Solids : Sand silt and Clay An increase in solids leads to less room for error and water, this will result in lower permeability.

Soil permeability

The ease with which gases, liquids or plant roots penetrate or pass through the soil