The Soil Community: Managing it for Better Crops Kristy Borrelli REACCH Extension Specialist kborrelli@uidaho.edu
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 N 2 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 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 Crop Health Quality Indicator Compaction and Friability Erosion Water Holding Capacity, Drainage, Infiltration Nutrient Holding Capacity Earthworms Organic Matter High Quality Soil Healthy leaves, normal growth across field, roots branched and extended throughout soil Soil crumbles well, easy to penetrate No gullies, rills or runoff Little drought stress, no ponding or runoff Soil tests trending up in relation to fertilizer applied Abundant, a lot of casts and holes 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. 2 nd 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 Release plant nutrients 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 Rapid Decomposition Very Slow Decomposition Enzymatic Oxidation R (CH 2 O) + Oxygen > CO 2 + H 2 O + 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+ cmol c /kg exchange Clays: 100 200 cmolc/kg Brady and Weil (2002). The nature and properties of soils. 13 th ed.
Soil Composition
Adding Organic Matter Leads to Healthy Plants Increased biological activity and diversity Reduced soil borne diseases and parasitic nematodes Pore structure improved Improved tilth and water storage Adapted from Magdoff and van Es. 2000 Aggregation increased Humus Decomposition Nutrients released Healthy Plants Harmful substances detoxified
Organic Matter Management
How do soils become degraded? Building Soils for Better Crops. 2 nd 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 CO 2 eq Cumulative effect of 3.2 3.5 tons/ha CO 2 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
High Quality Soil 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