PurposeTo determine the bulk density of each soil horizon at the GLOBE soil study sites. OverviewBulk density is defined as the ratio of the mass of dry solids to the bulk volume of the soil. Students will take 3 bulk density samples from each horizon of the soil profile they sample at each of the study sites. A soil sampling can of known volume will be used. An auger may also be used, and the diameter and length of the hole must be recorded for each sample to determine its volume. The sample will be taken back to the classroom, weighed, oven dried, and reweighed. Rocks need to be separated from the dried sample, either by seiving, or by picking out the rocks carefully and their density of the rocks determined. Data reported on the GLOBE Data Entry Sheet include: volume of can (or diameter and depth of auger hole for each sample), weight of can, moist weight of soil sample plus can, dry weight of soil sample plus can, weight of rocks, volume of rocks for triplicate samples in each horizon. The final bulk density at the field moisture content for each soil horizon (in triplicate) can then be calculated. Time Required

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Knowing the bulk density of a soil is important for many reasons. Bulk density can give us information about how much porosity (number of pore spaces) are in a sample. This helps to determine how much air or water can be stored and moved through the soil. It also gives an indication of how tightly soil particles are packed together, and if it will be difficult or easy for roots to grow or shovels to penetrate through a soil horizon. Another important function of bulk density is using it to convert between weight and volume for a soil sample. If we know the weight of a soil sample, we can calculate what its volume is by dividing it by its bulk density. If we know the volume of a soil, we can determine its weight by multiplying it by its bulk density.
Sample volume = pi x (inside dia./2)^2 x sample thickness (cm3)The volume of rock, in terms of displaced water is:
Rock volume = Postrock volume  Prerock volume (mL = cm3)The bulk density (in units of g/cm3) can now be calculated for each sample by:
(Dry weight  Can weight)  Rock weight Bulk Density =  Sample volume  Rock volumeThe soil water content (SWC) of the soil at the time of sampling is equal to:
Wet weight  Dry weight Soil Water Content =  Dry weight  Can weight
Porosity (%) = bulk density / particle density
Handson protocol. Will help to integrate soils with other aspects of the ecosystem by better describing soil properties related to rooting depths, porosity, hydraulic conductivity, and others. Also allows conversion of units for modeling purposes, and scaling of soil properties to larger areas.