Organic Matter

What is organic matter

Nature of O.M.

• 1. Is the portion of the soil which includes animal and plant remains at stages of decay–Forest= leaves, dead trees, –Prairies=grass roots and tops–Farmland= crop residue

Chemical Makeup of O.M.

• 1. Consists of complex carbon-containing compounds

• 2. Long chains are formed and other elements use these to make more organic compounds

Chemical Makeup of O.M

• 3. The most important compounds are–A. Carbohydrates: simple

sugars, starches, and cellulose–B. Lignins: is 10-30% of plant

tissue, makes plants rigid, resists decay

Chemical Makeup of O.M

–C. Protein

•Amino acid chains

•Supplies N when broken down

Decomposition

• 1. Micro-organisms digest organic matter

• 2. Releases CO2 and H2O• 3. Carbohydrates are first to be

consumed• 4. Lignin-becomes humus and

slowly broke down

Decomposition

• 5. Decay Organisms need O2 and microorganisms use O2 to oxidize the different compounds

• 6. 1st breakdown is quick and requires weeks or months

• 7. Well drained soils will lose 1-3% of humus a year to oxidation

Factors affecting O.M.

• 1. Vegetation

–2 times as much o.m. on grassland to woodland

–O.M. is deeper in prairie soil and is in soil

Factors affecting O.M.

• 2. Climate

–Arid conditions soil has less O.M.

–High temperatures decay O.M. more rapidly

Factors affecting O.M.

• 3. Texture

–Fine textured soils hold more organic material because clay protects hums from decay

Factors affecting O.M

• 4. Tillage

–Prairie will return more than cropping

Functions of O.M.

• A. Nutrient and water storage–1. O.M. stores many of the

nutrients used by plants and does it in 2 different ways•Colloids hold water and nutrients•O.M. stores nutrients as part of its own makeup

Functions of O.M.

–2. Both humus and O.M. absorb water like a sponge, humus can store 6 times its own weight

Functions of O.M.

• B. Nutrient Availability

–Makes several nutrients more available for plant use

Functions of O.M

• C. Soil Aggregation

–1. Heavy clay responds best. Breaks down particles, aerates, and makes easier to work with

Functions of O.M

• D. Prevents Erosion–1. Soils kept supplied with O.M.

have improved structure that improves water infiltration

–2. Stops excessive water runoff–3. Increasing O.M. from 1-3%

will reduce erosion 1/5-1/3

Functions of O.M.

• Undesirable Effects

–1. Nitrogen is immobilized or tied up during the decay process and is unavailable to plants

–2. Certain plant residues are toxic to other plants

Maintaining Soil O.M.

• A. It is impractical and not economical to raise O.M. levels significantly but should be a goal to maintain at highest levels

Maintaining Soil O.M.

• B. Adding fresh organic matter will improve soil the best

Maintaining Soil O.M.

• C. Crop Residues–Leave all crop materials

possible. Don’t burn residues, harvest some

–Use good fertilizer, healthy plants make more residue

Maintaining Soil O.M.

• D. Green Manure–1. Turn over alfalfa, clover,

sudan grass, will increase N levels

–2. Increases O.M. levels and fixes more nutrients

Maintaining Soil O.M.

• E. Crop Rotation

–1. A rotation between row crops, small grains, and legumes is better for keeping high O.M.

Maintaining Soil O.M.

• F. Organic Matter Additions–1. Animal Manures, sludge,

organic wastes–2. Industries may provide

organic wastes, by products, meat scraps, etc.

Maintaining Soil O.M.

• G. Mulches–1. Not economical in large acres–2. Reduce tillage leaves some

mulch–3. Limits water evaporation,

keeps soil temperature cooler on hot days, and warmer at night

Maintaining Soil O.M.

–4. Horticulture crops are mulched

Maintaining Soil O.M.

• H. Conservation Tillage–1. Conserves topsoil which is

high in O.M.–2. Crop residue decays slower

when left on top–3. No till soils are high in O.M. in

the top layer

Nitrogen Tie-up and Composting

• A. Soil Microorganisms need both Carbon and N in their diet to grow and multiply–1. Fresh organic matter will

increase number of organisms because higher food supply

Nitrogen Tie-up and Composting

–2. They compete with plants for N and can cause slow plant growth

Nitrogen Tie-up and Composting

• B. Carbon-Nitrogen Ratio (C:N ratio)

–1. The measure of carbon amounts compared to N amounts

–2. Plants with high c:n ratio’s are of greatest concern

Nitrogen Tie-up and Composting

–3. Matter with a low c:n ratio N rich

•A high c:n ratio is N poor

Nitrogen Tie-up and Composting

• Soil Humus 10 Garden Soil 12• Young Alf 12 compost 15-20• Rotted manure 20 Clover

residue 23• Corn stalks 60 Straw 60• Sawdust 400