1. Soil Physical Properties Used to Assess Soil Quality
Field Exercise

2. Two Ways to Assess Soil Quality
Measurements over time.
Comparing management systems.
Examples:
Side-by-side comparisons of management systems.
Measurements in the same field over time.
Problem areas versus non-problem areas.
Compare measured values to a reference soil condition or to the natural ecosystem.

3. Soil quality is assessed by measuring a number of soil properties to evaluate the soil’s ability to perform basic functions.
Physical Property:
Bulk Density
Porosity
Macroporosity
Microporosity
Air-Filled Porosity
Hydraulic Conductivity
Field Capacity
Plant Available Water
Aggregate Stability
Infiltration
Penetration Resistance
Condition:
Compaction
Aeration
Percolation
Infiltration
Drainage
Aggregation
Waterlogging
Erodibility
Crusting
Root Growth
Plant Growth

4. Bulk Density
The ratio of oven-dried soil (mass) to its bulk volume (g/cm3).
Range: 1.0 to 1.7 g/cm3.
Used to convert soil water content in percent by weight to percent by volume.
Used to calculate porosity.
Calculation: BD = Oven-Dry Soil Weight/Core Sample Volume
Indicator of: Compaction, aeration, root growth, microbial activity, infiltration, and drainage. 

5. Porosity That portion (%) of the soil not occupied by solid material.
The ratio of the soil pore volume to its bulk volume.
Calculation: Porosity (%) = 100 – 100(BD/PD) where, PD = Particle density.
Indicator: Compaction, aeration, aggregation, root growth, microbial activity, water movement and storage.

6. Macroporosity
That portion (%) of the soil occupied by pores of large size. Because of their large size, they are not able to retain water against gravity by capillary action.
The ratio of large pore volume to the soil bulk volume.
Calculation: % Water by volume at saturation - % Water by volume at field capacity.
Indicator: Compaction, aeration, aggregation, root growth, microbial activity, water movement and storage.

7. Microporosity
That portion (%) of the soil occupied by pores of small size –also called capillary pores. Because of their small size, they are able to retain water against gravity by capillary action.
The ratio of small pore volume to the soil bulk volume.
Calculation: % Total Porosity - % Macroporosity.
Indicator: Compaction, aeration, aggregation, root growth, microbial activity, water movement and storage.

8. Air-Filled Porosity
That portion (%) of the soil occupied by air-filled pores.
The ratio of air-filled pore volume to the soil bulk volume.
Calculation: % Water by Volume at Saturation - % Water by Volume at Sampling.
Indicator: Aeration, excessively wet conditions, microbial activity, drainage.

9. Saturated Hydraulic Conductivity
Indicator of the soil ability to conduct water (in/hr) in saturated conditions.
The ratio of the flow density or “flux” per unit hydraulic gradient.
Estimation: Soil Water Characteristics Calculator (
Indicator: Water movement, compaction, aggregation.

10. Field Capacity
The water content (in/ft) of soil after free drainage from a saturated condition.
The amount of water (in/ft) that a soil is able to retain after free drainage.
Calculation: (% Water Content by Volume)/100 x (12in/ft).
Indicator: Water retention, plant growth, rooting, microbial activity, compaction, aggregation.

11. Permanent Wilting Point
The water content (in/ft) below which plants are generally unable to extract water from the soil.
Calculation: (% Water Content by Volume)/100 x (12in/ft).
Estimation: Soil Water Characteristics Calculator (

12. Plant Available Water Holding Capacity
The quantity of water (in/ft) that a plant is able to extract from a soil at field capacity.
Calculation: Field Capacity (in/ft) – Permanent Wilting Point (in/ft).
Indicator: Available water retention, plant growth, rooting, microbial activity, compaction, aggregation.

13. Water Stable Aggregates (Aggregate Stability)
Measures the amount of stable aggregates (%) against flowing water.
Calculation: % Water Stable Aggregates = 100 [(Weight of Stable Aggregates)/(Weight of Aggregate Sample Used)].
Indicator: Soil erodibility.

14. Infiltration The entry of water into the soil (in/hr).
The height (in) of water entering the soil surface per unit time (hr).
Calculation: Water Height (in)/Time (hr).
Indicator: Water runoff, erosion.

15. Penetration Resistance (Soil Strength)
Soil resistance (kg/cm2) to penetration by a metal rod.
Calculation: Cone Index = force applied (kg)/cone tip basal area (cm2).
Indicator: Compaction, root proliferation, infiltration, drainage, microbial activity.

16. Measurement of Soil Physical Properties for Soil Quality Assessment
Parameter
Equation
Result 1
% Organic Matter 2
Soil Structure 3
Soil Color 4
% Sand 5
% Silt 6
% Clay 7
Textural Class

17. Soil Water Content at Sampling
Parameter
Equation
Result 8
Soil Moisture Sample Weight, g 9
Hydroscout Reading 10
Mass Wetness, g
#9 / (#8 - #9)

18. Collecting an Undisturbed Soil Core

19. Data From Undisturbed Core Sample
Parameter
Equation
Result 11
Ring Weight, g 12
Ring Diameter, cm 13
Ring Height, cm 14
Ring Volume, cm3 15
Weight Rubber Band + Dry Cloth, g 16
Weight Rubber Band + Cloth + Metal Core + Field Moist Soil, g 17
Weight Rubber Band + Cloth + Metal Core + Saturated Soil, g

20. Data From Undisturbed Core Sample
Parameter
Equation
Result 18
Weight Rubber Band + Cloth + + Metal Core + Drained Soil, g 19
Weight Rubber Band + Cloth After Drainage, g 20
Weight Rubber Band + Cloth Saturated, g 21
Core Sample Field Moist Weight, g 22
Core Sample Dry Weight, g 23
Bulk Density, g/cm3

21. Data From Undisturbed Core Sample
Parameter
Equation
Result 24
Weight of Water at Sampling, g 25
% Water at Sampling 26
Weight of Water at Saturation, g 27
% Water at Saturation 28
Weight of Water at Field Capacity, g 29
% Water at Field Capacity

22. Particle Density Determination
Parameter
Equation
Result 30
Weight of Moist Soil, g 31
Weight of Dry Soil, g 32
Weight of Flask Full of Water, g 33
Weight of Flask Full of Water + Soil, g 34
Particle Density, g/cm3

23. Calculation of Soil Physical Parameters
Equation
Result 35
% Porosity 36
% Macropores 37
% Micropores 38
% Air-Filled Porosity 39
Hydraulic Conductivity, in/hr 40
% Water PWP 41
% PAW

24. Calculation of Soil Physical Parameters
Equation
Result 42
Depth of Water at Saturation, in/ft 43
Depth of Water at Field Capacity, in/ft 44
Depth of Water at Sampling, in/ft 45
Depth of Water at PWP, in/ft 46
Depth of PAW, in/ft

25. Aggregate Stability Determination
Parameter
Equation
Result 47
Volume of Initial Aggregates + Gravel, cc 48
Volume of Stable Aggregates + Gravel, cc 49
Volume of Gravel, cc 50
Volume of Initial Aggregates, cc 51
Volume of Stable Aggregates, cc 52
% Water Stable Aggregates

26. Infiltration Parameter Equation Result 53 Infiltration Time, minutes54
Infiltration, in/hr
Soil Respiration 55
Soil Temp., oF 56
Soil Temp., oC 57
Draeger Tube Reading 58
Respiration, lbs CO2-C/acre/day 59
Penetration Resistance, kg/cm2

27. Property
Conventional
Tillage
Strip
Textural Class
Sandy loam
Sandy clay loam
% Sand, Silt, Clay
60 –
56 –
Soil Structure
Fine Moderate Blocky
Organic Matter, %
1.7
2.5
Soil Color
7.5 YR 4/6
7.5YR 3/4
Bulk Density, g/cm3
1.32
1.47
Total Porosity, %
47.4
41.4
Macroporosity, %
16.2
13.8
Microporosity, %
31.2
27.6

28. Property
Conventional
Tillage
Strip
Air-Filled Porosity, %
26.8
9.2
Hydraulic Conductivity, in/hr
2.05
1.20
Field Capacity, in/ft
3.1
3.5
Permanent Wilting Point
1.5
1.9
Plant Available Water, in/ft
1.6
Water Stable Aggregates, %
64.0
62.7
Infiltration, in/hr
Penetration Resistance, kg/cm2

29. Question 1: Based on the soil water content obtained from the core sample, determine the depth of water (inches) needed so that the upper foot of soil reaches field capacity. Conventional Tillage: Water Content at Sampling= 20.6% or 2.47 in/ft Field Capacity = 3.1 in/ft Answer: 3.1 – 2.47 = 0.63 in/ft Strip Tillage: Water Content at Sampling= 32.2% or 3.86 in/ft Field Capacity = 3.5 in/ft Answer: 0 in/ft

30. Question 2: Calculate the soil water content (in/ft) at 50% plant available water depletion. Next, calculate how much water (inches) needs to be added to the upper foot of soil to reach field capacity. Conventional Tillage: Soil Water 50% Depletion = PAW/2 + PWP = (1.6/2) = 2.3 in/ft (19.1 %) To reach FC add the amount depleted = 1.6/2 = 0.8 inches

31. Question 3: Use the soil water characteristic calculator to estimate the soil properties listed below. Compare the estimations with the results obtained from your samples.
Conventional Tillage
Strip Tillage
Actual
Estimated
Bulk Density, g/cm3
1.32
1.18
1.47
1.15
FC, in/ft
3.1
3.0
3.5
3.4
PAW
1.6
1.5

32. Question 4: Using the soil water characteristic calculator determine the effect of a two-fold increase in organic matter in each soil environment. Any improvements?
Conventional Tillage
Strip Tillage
Actual
Two-fold OM
Bulk Density, g/cm3
1.32
1.18
1.47
1.12
FC, in/ft
3.1
3.5
3.9
PAW
1.6
1.8
1.5
1.9