Testing for Bulk Density of Soil

The bulk density of soil refers to how compact it is. Soil that is too compact does not allow for much water or root formation. Looser soils tend to allow water to penetrate deeper into the ground, nourishing root systems and helping seedlings take root. Taking a core sample of soil makes it possible to calculate the bulk density of the soil. This is a fairly simple process that helps experts in the soil conservation field determine areas where the soil needs to be improved.

Things You'll Need

• 3-inch metal ring
• Wood block
• Sledgehammer
• Plastic bag
• Scale
• Trowel
• Flat bladed knife
• Microwave
• Microwavable container

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Instructions

• 1

  Drive the 3-inch metal ring into the ground. Place the wood block over the ring to protect it and use the sledgehammer to drive the ring into the soil until the top of the ring is even with the top of the soil. This sample provides a measurable volume for your calculations.

• 2

  Dig the ring out of the soil. Use the trowel to dig around and under the ring. You want to dig the ring out without losing any of the dirt inside it. One you have pulled it out, use your knife to remove any soil sticking out of the end. The level of soil should be even with both ends of the ring.

• 3

  Dry the soil. For your calculations to be accurate, you need to know the weight of the sample without water. First, break up the soil sample in the bag to loosen it for drying. Weigh your microwavable container and record its weight in grams, then dump the soil sample into the container and record its weight. Subtract the weight of the container from the weight with the sample. Put the container in the microwave for two minutes at a time, weighing the sample each time. The weight will drop as the water evaporates.

• 4

  Calculate the dry soil weight. When the weight of the sample stays the same after two or more readings, it means all the water is cooked out. For our example, we will say that the dry weight of the soil is 600 grams.

• 5

  Calculate the volume of the original sample. The volume of a cylinder is expressed this way: 3.14 (Pi) x r2 x H. The radius is half of your diameter. So, if your diameter is 8 cm, then your radius is 4 cm. Let's say the height is 10 cm. So, your calculation would be 3.14 x 4 x 4 x 10 = 502.4 cm.

• 6

  Calculate the bulk density. The formula for bulk density calculations is the dry soil's weight divided by the soil's volume. So, for our example, we would divide 600 by 502.4 to get a density of 1.2.