Soil Aggregate Stability: Tillage, Rotations, and …...Adapted from Sylvia et al., 2005, Principles...
Transcript of Soil Aggregate Stability: Tillage, Rotations, and …...Adapted from Sylvia et al., 2005, Principles...
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Soil Aggregate Stability:Tillage, Rotations, and Cover Crop Effects
Caley Gasch [email protected]
@ckgasch
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A unit of soil structure generally < 10 mm in diameter and formed by natural forces and substances derived from root exudates and microbial
products which cement smaller particles into larger units
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Adapted from Sylvia et al., 2005, Principles and Applications of Soil Microbiology
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Weil & Brady, 2017, The Nature and Properties of Soils
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Aggregates are characterized by size:
Free particles: < 0.053 mm
Microaggregates: 0.053 – 0.25 mm
Macroaggregates: 0.25 – 2 mm
Aggregates are stabilized by:
• Microbial and root polysaccharides and glycoproteins, which act as cement
• Fungal hyphae, actinomycetefilaments, and roots bind particles together like rebar and rope
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Functions of aggregates
• Soil stabilization Erosion prevention, trafficability
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Weil & Brady, 2017, The Nature and Properties of Soils
Functions of aggregates
• Soil stabilization
• Porosity and pore connectivity
Erosion prevention, trafficability
Water and air exchange & storage
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4“ (~10 cm)
6“
(~1
5 c
m)
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Functions of aggregates
• Soil stabilization
• Porosity and pore connectivity
• Organic matter and nutrient storage
Erosion prevention, trafficability
Water and air exchange & storage
Nutrient source, carbon storage
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Pulverized Intact
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Functions of aggregates
• Soil stabilization
• Porosity and pore connectivity
• Organic matter and nutrient storage
• Creation of microscale heterogeneity
Erosion prevention, trafficability
Water and air exchange & storage
Nutrient source, carbon storage
Soil habitat diversity
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microbes
Orgiazzi et al., 2016, The Global Soil Biodiversity Atlas
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Practical considerations of aggregates
• Soil texture influences aggregation
• Aggregates are round, not blocky or angular
• Physical disturbance breaks down aggregates
• Soils should have a variety of aggregate sizes
Paul, 2007, Soil Microbiology, Ecology, and Biochemistry
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Management and Aggregates
Jastrow, 1996, Soil Biology and Biochemistry 28: 665
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> 2 mm
Macro – aggregates250 𝛍m – 2 mm
Micro – aggregates53 – 250 𝛍m
Free particles
% Stability(sum of aggregated mass)
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> 2 mm
Macro – aggregates250 𝛍m – 2 mm
Micro – aggregates53 – 250 𝛍m
Free particles
% Stability(sum of aggregated mass)
Size fractions that are sensitive to management
Higher % = more aggregate function
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Management & Factors Aggregate formation and stability
Tillage ↓↓↓
Roots ↑↑↑
Rotational diversity ↑↑
Earthworms ↑
Salinity & Inundation ↓
Coarse mineral particles ↓↓
Organic matter ↑↑
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Measuring Aggregates: In the field
• Spade test
• Appearance
• Crumbly structure
Sampling Aggregates
• Spade or wide probe
• Soils near field capacity
• Top 6” or rooting zone
• Not necessary every year
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Measuring Aggregates: The slake test
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Measuring Aggregates: In the lab
Cornell Soil Health
Wood’s End VASTBenchtop wet sievingManual wet sieving
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