Unit BULK DENSITY OF SOIL
Objectives 1. Describe the concept and importance of soil density. 2. Determine soil density. 3. Explain how to alter soil density. 4. Describe the effect of soil density on erosion, water holding capacity and flooding.
Terms Bulk density Consistence Particle density Structure Texture
Describe the concept and importance of soil density. What is bulk density?
- Bulk density is a measurement of how tightly soil particles are pressed together. - Density is the mass of an object divided by the volume.
Bulk density - Texture, the relative proportion of soil separates in a soil, affects the density, as different separates have different masses and have corresponding pore space.
Structure - the arrangement of soil particles into aggregates or peds, also determines density because various soil arrangements will compact more easily than others.
Particle Density - of the soil is the mass per unit volume of soil particles excluding the pore space.
-The soil consistence, the soil’s response to pressure at various moisture levels, can be described as hardness, friability, stickiness, and plasticity.
Determine soil density. How can you determine soil density?
- Soil density is the mass of the soil particles divided by volume. - When removed from the earth’s crust the soil contains air and water that will affect the mass readings and do not constitute soil density.
- The soil needs to be dried in order to find the true density. - Density is usually expressed in grams per cubic centimeter.
Explain how to alter soil density. How can you change soil density?
- Soil density is affected by tillage and non-tillage systems. - The working of the subsoil by a subsoil tillage system can decrease the density of the soil by encouraging more pore space per volume.
B. Some seedbeds and fields have too little soil density so rolling the field or working the soil with a finisher may provide better seedbed density.
- At construction sites it is important to have a compacted subsoil so settling will not occur once the building is completed.
Describe the effect of soil density on erosion, water holding capacity, and flooding. What effect does soil density have on various soil characteristics?
IV. Soil density affects soil characteristics. A. With higher the soil density the amount of pore space decreases, thus decreasing the water holding capacity of the soil. This decrease in water holding capacity is especially significant in the larger pore spaces that are readily available to hold water which plants can utilize.
Erosion • can also be affected by density, as water will not infiltrate the soil as readily • will stay in contact with the topsoil for a longer period of time.
Flooding • Flooding will result from excessive runoff and decreased infiltration in wet years. • Puddling can result from localized compaction, as is the case in tractor tire ruts.
Bulk Density Equation. oven - dry weight in grams Bulk density = volume of cylinder in cubic centimeters