1. CE/ENVE 320 – Vadose Zone Hydrology/Soil Physics Spring 2004 Copyright © Markus Tuller and Dani Or 2002-2004 Soil Bulk Density and Compaction Hillel, pp. 12 & 112 4

2. Copyright© Markus Tuller and Dani Or2002-2004 Determination of Bulk Density To determine bulk density we need to measure the dry mass and the total volume occupied by the soil sample. CORE METHOD: A cylindrical metal sampler is driven into the soil to remove a known volume (core). The core (soil + brass cylinder) is oven-dried at 105 o C to remove non-structural soil water till the mass remains constant (usually after 24–48 hrs).

3. Copyright© Markus Tuller and Dani Or2002-2004 Core Method Volume Cylinder Dry Mass Sample Oven 105 o C

4. Copyright© Markus Tuller and Dani Or2002-2004 Core Method - Example r = 3 cm h = 12 cm M s = 480 g (oven-dry mass) r h

5. Copyright© Markus Tuller and Dani Or2002-2004 Excavation Methods – Sand Funnel A quantity of soil is excavated in the field, dried at 105 o C and weight. The volume is determined by filling the excavated hole with a well defined standard sand of which the volume per unit mass is known. (SAND-FUNNEL Method) Valve Standard Sand Base Plate

6. Copyright© Markus Tuller and Dani Or2002-2004 Excavation Methods – Rubber Balloon Water Tower with Scale In the RUBBER BALLOON Method the volume is determined by inserting a balloon into the excavation and filling it with water or an other fluid with known density. Rubber Membrane Valve

7. Copyright© Markus Tuller and Dani Or2002-2004 Bulk Density – Clod Method The clod method is based on measuring volume and mass of a wet clod sampled in the field according to the following steps. 1.Sample clod and put it into a nylon hairnet of known mass. Weigh clod +hairnet. 2.Coat the clod with Saran solution to make it waterproof. Apply 2-3 layers and allow 15-30 min drying time for each layer (solvent evaporates). Weigh container with saran before and after coating to determine the mass of saran covering the clod. 3.Weigh clod with coating and hairnet. Weigh clod again when it is suspended in water at known temperature (Archimedes principle). 4.To correct for water content of the soil, break open the clod and take a small sub-sample. Weigh sub-sample before and after oven drying.

8. Copyright© Markus Tuller and Dani Or2002-2004 Bulk Density – Clod Method CLOD METHOD:

9. Copyright© Markus Tuller and Dani Or2002-2004 Clod Method 5.Calculate oven-dry mass of clod: where M w is the wet weight of the clod (corrected for the hairnet), and q m is gravimetric water content determined for the sub- sample. 6.Calculate bulk density:

10. Copyright© Markus Tuller and Dani Or2002-2004 Bulk Density – Gamma Rays GAMMA RAY TECHNIQUES: Gamma ray techniques are based on attenuation and diffraction of gamma rays emitted from a 137 Caesium or 241 Americium source due to collision with other atoms of the soil phases. Attenuation and diffraction are dependent on bulk density and other soil properties (e.g., water content)

11. Copyright© Markus Tuller and Dani Or2002-2004 Gamma Rays TRANSMISSION TECHNIQUE: Two probes at a fixed spacing are lowered into previously prepared openings in the soil. One probe contains a Geiger tube, which detects the attenuated radiation transmitted through the soil from the gamma source located in the second probe.

12. Copyright© Markus Tuller and Dani Or2002-2004 Gamma Rays SCATTERING TECHNIQUE: A single probe contains both, detector and source separated by shielding. Can be used on the surface or placed in a hole dependent on design of the equipment.

13. Copyright© Markus Tuller and Dani Or2002-2004 Gamma Ray SCATTERING TECHNIQUE: A single probe contains both, detector and source separated by shielding. Can be used on the surface or placed in a hole dependent on design of the equipment.

14. Copyright© Markus Tuller and Dani Or2002-2004  In agriculture and forestry soil compaction is undesirable.  For many engineering applications a well compacted soil is crucial for safe foundations (the Leaning Tower of Pisa is an example of building on soft soil). Soil Compaction – desired or not? Image: Opera Primaziale Pisana

15. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction Low porosity (n) or high bulk density (  b ) are indicators for soil compaction. Soil compaction results in mechanical impedance to plant root growth, poor aeration, and reduced water infiltration. forest ecosystems are extremely sensitive to soil compaction! Compaction associated with timber harvest operations could disturb ecosystem for many years.

16. Copyright© Markus Tuller and Dani Or2002-2004 ·Operation of heavy vehicles (e.g. harvesters, construction machines) on agricultural land can cause soil compaction. Agricultural Soil Compaction – Causes

17. Copyright© Markus Tuller and Dani Or2002-2004 ·Compaction alters soil hydraulic and gaseous exchange properties and increases mechanical impedance to plant roots. Soil Compaction – Indicators

18. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction - Agriculture

19. Copyright© Markus Tuller and Dani Or2002-2004 ·Compaction hampers plant growth and decreases crop yield. ·The extent of soil degradation due to compaction exceeds an area of 6.8x10 4 km 2 worldwide (Oldeman 1991). Soil Compaction – Effects

20. Copyright© Markus Tuller and Dani Or2002-2004 Visualization of effect of compaction on flow Water flow pathways are visualized using dye tracer experiments The resulting distribution of dye tracer in the soil reflects the degree and patterns of soil compaction.   (Kulli 2001)

21. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction – Effects on pore spaces

22. Copyright© Markus Tuller and Dani Or2002-2004 Modeling effects of soil compaction on pore space mm mm mm mm mm mm Results from uniaxial compression tests of soil samples at different initial water potentials (Berli, 2002) were in agreement with pore closure model (Ghezzehei & Or, 2002).

23. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction – agricultural practices Subsoiler

24. Copyright© Markus Tuller and Dani Or2002-2004 Mechanical impedance to root growth A tillage pan has been mechanically broken by a subsoiler. Roots penetrate into the subsoil through the subsoiler slot to access water and nutrients.

25. Copyright© Markus Tuller and Dani Or2002-2004 Mechanical impedance to root growth Loose zone Subsoiling Chisel Plowpan Root distribution of a cotton plant

26. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction – Gas flow (aeration) Surface compaction can be partially reduced with an aerator

27. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction – Aeration The aerator cuts and removes small cores from the top few centimeters, thereby creating vertical channels for improved infiltration and aeration.

28. Copyright© Markus Tuller and Dani Or2002-2004 Soil Compaction – Aeration