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Soil Physical Properties Used to Assess Soil Quality

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

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Soil Physical Properties Used to Assess Soil Quality

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  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. Physical Property: Bulk Density Porosity Macroporosity Microporosity Air-Filled Porosity 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 Soil quality is assessed by measuring a number of soil properties to evaluate the soil’s ability to perform basic functions.

  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 (http://www.pedosphere.com/resources/texture/triangle_us.cfm • 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 (http://www.pedosphere.com/resources/texture/triangle_us.cfm).

  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

  17. Soil Water Content at Sampling

  18. Collecting an Undisturbed Soil Core

  19. Data From Undisturbed Core Sample

  20. Data From Undisturbed Core Sample

  21. Data From Undisturbed Core Sample

  22. Particle Density Determination

  23. Calculation of Soil Physical Parameters

  24. Calculation of Soil Physical Parameters

  25. Aggregate Stability Determination

  26. Infiltration

  27. 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/ftField Capacity = 3.1 in/ftAnswer: 3.1 – 2.47 = 0.63 in/ftStrip Tillage:Water Content at Sampling= 32.2% or 3.86 in/ftField Capacity = 3.5 in/ftAnswer: 0 in/ft

  28. 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 Content @ 50% Depletion = PAW/2 + PWP = (1.6/2) + 1.5 = 2.3 in/ft (19.1 %)To reach FC add the amount depleted = 1.6/2 = 0.8 inches

  29. 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.

  30. 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?

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