The Soil Community: Managing it for Better Crops
Kristy Borrelli
REACCH Extension Specialist
[email protected]
Outline
• Soil Community
• Soil Quality
• Soil Organic Matter and Carbon
• Soil Organic Matter Management
The Soil Community
Soil Biology
• 1 gram of soil contains >1 million organisms
• They influence soil characteristics and plant health
Reganold, J.P., R.I. Papendick and J.F. Parr. 1990.
Sustainable agriculture. Scientific American. 262(6):112-120.
Soil Biota
Beneficial Effects of Soil Organisms
1) Decomposition and Transformation
2) Nitrogen Fixation
3) Phosphorus Assimilation
4) Plant Protection
1) Decomposition and Transformation
• Bacteria, fungi, macrofauna
etc.
• Mineralization – Make nutrients plant available
– Synthesize new compounds (humus) that stabilize soil
• Inorganic transformations
– Metals
– Plant nutrients • Breakdown toxic compounds – Agrichemicals – Metabolic by‐products
Degradation of organic matter residues
2) Nitrogen Fixation
• Bacteria
• Symbionts or free‐living • Converts atmospheric N2 to plant available form • Associated with legumes
– Good for crop rotations
– Reduce N fertilizer inputs
http://lifeofplant.blogspot.com/2011/03/nitrogen‐fixation.html
3) Phosphorus Assimilation
• Mycorrhizae
– Fungi/plant root symbioses
– Mutual benefit
• Plants nutrients, fungi sugar
• Improve ability to scavenge water and nutrients (~10x) – Especially Phosphorus
– Increase resilience to drought
• Protect plants from high concentrations of metals, salts or parasites
• Exudates help stabilize soil
http://www.morning‐earth.org/Graphic‐E/BIOSPHERE/Bios‐C‐PlantsNew.html
4) Plant Protection
• Bacteria
• Disease Suppression
• Suppressive soil can be – Specific – 1 organism
– General – group of organisms
• Mechanisms
– Direct parasitism
– Nutrient competition
– Direct inhibition –
secretion of antibiotics
Decrease in the incidence and severity of take‐all that occurs with monoculture of wheat or barley
Soil Quality
Soil Quality
The capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to •
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Sustain plant and animal productivity
Maintain and enhance water and air quality
Withstand resilience to stress
Support human health and habitation High Quality Soil
has structure
Low Quality Soil does not
Soil Composition
Soil Structure
The combination of sand, silt and clay (with organic matter) into secondary particles called aggregates
Soil Aggregation
Soil Quality Indicators
Quality Indicator
High Quality Soil
Crop Health
Healthy leaves, normal growth across field, roots branched and extended throughout soil
Compaction and Friability
Soil crumbles well, easy to penetrate
Erosion
No gullies, rills or runoff
Water Holding Capacity, Drainage,
Infiltration
Little drought stress, no ponding or runoff Nutrient Holding Capacity
Soil tests trending up in relation to fertilizer applied
Earthworms
Abundant, a lot of casts and holes
Organic Matter
Dark surface soil, abundant surface residue
Soil Organic Matter and Carbon Soil Organic Matter (SOM)
• A typical agricultural soil has 1 to 6% organic matter
• SOM is a complex mixture of living, dead and decomposing material
• Dynamic nature and complex chemistry
Soil Organic Carbon (SOC)
• Soil Carbon is a main component of all organic building blocks; so SOC often is associated with SOM
• World soils contain about 3x as much Carbon as all of the vegetation in the world Natural Carbon Cycle
Building Soils for Better Crops. 2nd edition. Magdoff and van Es. 2000
Three Parts of SOM
1) Living
2) Dead
3) Very Dead
1) Living
• Living Organisms
– Plants, microbes and mega fauna
– Shed organic materials – Leave sticky residues (polysacchrides, proteins, glomalin) that aid in soil aggregation
Rhizodeposition – total nutrients and C coming from roots
Sources of Rhizodeposition
1) Cap and boarder cells
2) Insoluble mucilage
3) Root exudates
4) Volatile organic carbon
5) Carbon to symbionts
6) Death of root cells
http://www.nature.com/scitable/knowledge/library/the‐rhizosphere‐roots‐soil‐and‐67500617
http://www.nature.com/scitable/knowledge/library/the‐rhizosphere‐roots‐soil‐and‐67500617
Rhizosphere
• Plant‐Root interface
• 2 mm surrounding root surface
• High concentration of microbes
• Gradient in chemical, physical and biological properties
– Differs from bulk soil Coats and Rumpho, 2014. Microbiol. Root Diversity
© 2012 Nature Education 1995 Conservation Research Institute, Heidi Natura. All rights reserved
2) Dead
• Fresh plant residues, dead organisms, manure and organic waste.
– Active fraction of SOM, main food supply
– As they decompose Æ Release plant nutrients
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Proteins
Amino Acids
Simple sugars
Starches
Inorganic nutrients
Plant Residue Decomposition
Sugars, Starches, Simple Proteins
Crude Proteins
Hemicellulose
Cellulose
Fats, Waxes, Cutin etc.
Lignin and Phenolic Compounds
Enzymatic Oxidation
Rapid Decomposition
Very Slow Decomposition
R‐(CH2O) + Oxygen ‐‐‐‐‐‐‐‐‐‐‐‐> CO2 + H2O + Energy
3) Very Dead
• Well‐Decomposed Organic Matter
– Humus – Chemically Complex
• Fulvic Acids
• Humic Acids
• Phenolic compounds
– Not a food source – difficult to degrade
Structure of Humus
200+ cmolc/kg exchange
Clays: 100‐200 cmolc/kg Brady and Weil (2002). The nature and properties of soils. 13th ed. Soil Composition
Adding Organic Matter Leads to Healthy Plants
Increased biological activity and diversity
Reduced soil borne diseases and parasitic nematodes
Aggregation increased
Humus
Pore structure improved
Improved tilth and water storage
Adapted from Magdoff and van Es. 2000
Decomposition
Nutrients released
Harmful substances detoxified Healthy Plants
Organic Matter Management
How do soils become degraded?
Building Soils for Better Crops. 2nd edition. Magdoff and van Es. 2000
What if you don’t take care of your soil?
Images from Amazon.com
Conserving SOM
1) Add Organic Matter
2) Grow Organic Matter
3) Manage Organic Matter
1) Add Organic Matter • Organic waste materials can be added to soils to improve SOM content
• Examples: Animal Manure, Compost, Biosolids, Biochar, Bloodmeal, Fishmeal, Bonemeal, Kelp, Commercial Fertilizers, Food and Industrial Wastes
Add Organic Matter
• Recycle organic amendments
2) Grow Organic Matter
• Produce, recycle plant residues (straw, roots)
• Use soil building crop rotations
– Green manures
– Legumes
– Cover crops
– Broadleaves and grasses
Grow Organic Matter
• Usually not an entirely complete source of nutrients, but often can supply C and N to a soil. • Stimulates microbial activity.
• Not grown for cash crops to avoid harvesting of nutrients (green manures and cover crops)
• Cash crops also contribute OM – roots and above ground residue
Grow Organic Matter
Brassica Green Manures
“It’s like gaining a day in terms of water… You have a bigger cusion for surviving without crop damage”
McGuire, 2003. Plant Management Network
Brassica Green Manures
• SOM – 1997 = 0.6%
– 2010 = 1.2% • Carbon sink
– 700 kg CO2 eq
– Cumulative effect of
– 3.2 – 3.5 tons/ha CO2
sequestered Effective nematode control
Lazzeri and D’Avino, 2010. Acta Hort. 3) Manage Organic Matter
• Organic matter should be properly managed in order to reduce soil disturbance and oxidation of carbon compounds. • Example: Conservation tillage
Manage Organic Matter
• Control erosion and topsoil losses
• Reduce or eliminate tillage
• Reduce compaction – resiliency to stress
ACZ 2 = Annual Crop: Wet‐Cold
ACZ 3 = Annual Crop: Fallow‐Transition
ACZ 5 = Grain‐Fallow
Brown, T.T. and D.R. Huggins. 2012. Soil carbon sequestration in the dryland cropping system region of the Pacific Northwest. J. Soil Water Conserv. 67:406‐415. Maintaining Soil Organic Matter and preventing its loss can improve soil quality.
Use multiple practices
Diverse sources of organic matter
Reduce losses of native soil organic matter
Protect soil surface from raindrops and temperature extremes
• Be conscious of driving field equipment over soil
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High Quality Soil •
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Spongy soil = Good structure
Water infiltration and storage
Root growth, depth and oxygen availability
Populations of soil organisms
Retains and provides crop nutrients
Resists degradation and is resilient to compaction
Filter toxins and heavy metals
High Source of CEC