Organic Matter The key to healthy soils Fred Magdoff Dept. of Plant & Soil Science University of Vermont

Characteristics of Healthy Soils Sufficient (but not excess) nutrients Good tilth Sufficient depth Good water storage and drainage Free of chemicals that might harm plants

Characteristics of Healthy Soils Low populations of plant disease and parasitic organisms High populations of organisms that help plant growth Low weed pressure Resistance to being degraded Resilience

There are three general “types” of organic matter in soils Living Dead Very Dead

plant roots bacteria nematodes —Living — fungi earthworms mites springtails moles

—Dead — Recently dead soil organisms and crop residues provide the food (energy and nutrients) for soil organisms to live and function. Also called “active” or “particulate” organic matter.

—Very Dead — Well decomposed organic materials, also called humus. Humus contains very high amounts of negative charge.

All three “types” of soil organic matter play important roles in helping produce high yields of healthy crops.

Soil organic matter living 10-20% Organic matter is 1-6% of total soil mass humus (very dead) 60-80% active (dead) 10-20%

Organic Matter Influences a Vast Number of Important Soil Properties For Example: Nutrient availability Aggregation (and infiltration and drainage) Water storage Diversity and activity of soil organisms Soil color Presence of growth stimulating compounds Important global cycles — carbon, nitrogen, and water — are strongly influenced by soil organic matter

Nutrient Availability

As organic matter is decomposed nutrients are transformed into forms that are available to plants.

From 50% to close to 100% of the CEC is due to soil organic matter

Cation Exchange Capacity and Chelation

Corn grown in nutrient solution with (right) and without (left) humic acids. Photo by R. Bartlett.

Soil Tilth

b) soil crusts after aggregates break down infiltration runoff a) aggregated soil b) soil crusts after aggregates break down

Root heavily infected with mycorrhizal fungi (note round spores at the end of some hyphae). Photo by Sara Wright.

HEALTHY PLANTS Add organic matter Increased biological activity (& diversity) Reduced soil-borne diseases, parasitic nematodes Aggregation increased Decomposition Pore structure improved Nutrients released Humus and other growth promoting substances Harmful substances detoxified Improved tilth and water storage HEALTHY PLANTS

Building Healthy Soil 1. Add plentiful amounts of organic materials — crop residues (including cover crops) as well as off-field sources such as animal manures and composts.

Average for three soils (sand, loam, and clay) Water stable aggregates following addition of 1% dm basis of dairy manure compost, small grain straw, grass clippings, or dairy manure. 62 a Average for three soils (sand, loam, and clay) 60 Water stable aggregates 0.25 to 4 mm diameter as a percent of total soil 58 56 b 54 52 b, c 50 48 46 c 44 c 42 40 ch comp. str. grass manure

Building Healthy Soils 2. Keep the soil covered with living vegetation and/or crop residue.

Use cover crops or perennial sod cover routinely. Reduce tillage intensity.

Building Healthy Soils 3. Use better crop rotations.

Grow perennials as well as annual crops Different rooting depths Different growth and harvest times Some high-residue crops Different crop families Etc.

Building Healthy Soils 4. Reduce tillage intensity.

Many different reduced till systems — conservation till, ridge till, no-till. Better planters help. Cover crops can help.

Building Healthy Soils 5. Use other practices that reduce runoff and erosion.

Grassed waterways terraces strip cropping along contour etc.

Runoff from soil with vegetative cover Runoff from bare soil Runoff from soil with vegetative cover

organic materials (crop residues, Use Multiple Tactics Better nutrient timing, placement, and amounts Reduce tillage Reduce compaction Cover crops Healthier Crops Better rotations Control erosion Add various sources of organic materials (crop residues, manures, composts, etc.)