Organic Matter In The Soil Topic #2055 Megan Burgess

Overview §Chemical/Physical Influence on Soils §Organic Matter Components §Humus §Effects of Organic Matter on Carbon: Nitrogen Ratio §Benefits of Organic Matter §Detrimental Effects

Chemical/Physical Influence on Soils §Life in soils is dependent on organic matter for energy and nutrients §Accumulation of organic matter reaches equilibrium in non-tilled soils §Organic matter can be temporarily added to increase to benefit soils for farming and gardening

Organic Matter Components §Living and dead plants §Animal residues l Insects l Earthworms l Macro and microorganisms

Organic Matter Components §Most comes from plants l 90% of plant material made of Carbon (C), Hydrogen (H), and Oxygen (O) l Moisture content of plants varies 60% - 90% (75% is average) l Other plant elements include: Nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, micronutrients

Organic Matter Components

§Animals - secondary sources of organic matter l Consume plant tissue and leave waste products and bodies when they die l Move plant residues (ex. earthworms, ants) §Bacteria, Fungi, Microorganisms - bulk of organisms l Breakdown plant and animal residues l Die and decompose into organic matter

Humus §Complex, amorphous, colloidal substance in soil left after decomposition of organic matter l Resistant to further decomposition l Improves soil structure l Dark color to soil (top 10 inches) l Increases soil water-holding capacity

Effects of Organic Matter on Carbon: Nitrogen Ratio §Natural conditions: l 12 parts carbon : 1 part nitrogen §Changes in components can change C:N ratio l Fungi and bacteria multiply rapidly l Temporary nitrogen deficiency for crop l As more organic matter is added the ratio changes

Benefits of Organic Matter §Source of 90-95% nitrogen in unfertilized soils §Major source of phosphorus and sulfur §Supplies soil aggregating cements §Contributes to cation exchange capacity §Increase soil water-holding capacity §Increases air and water flow rates

Benefits of Organic Matter §Increase micronutrient availability for plants §Furnishes carbon supply §Reduces erosion §Shades soil §Prevents rapid water loss §Balances soil temperature

Detrimental Effects §Energy source for disease organisms §Excessive plant residues may hinder planting operations §Some plants contain phytotoxins (poisons) in organic matter §Increase organic matter changes C:N ratio and limits availability to crops