August 2008 Organic Matter What is organic matter Original Power Point Created by Darrin Holle Modified by Georgia Agricultural Education Curriculum Office June 2002

August 2008 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

August 2008 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

August 2008 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

August 2008 Chemical Makeup of O.M –C. Protein Amino acid chains Supplies N when broken down

August 2008 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

August 2008 Decomposition 5. Decay Organisms need O2 and microorganisms use O2 to oxidize the different compounds 6. 1 st breakdown is quick and requires weeks or months 7. Well drained soils will lose 1-3% of humus a year to oxidation

August 2008 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

August 2008 Factors affecting O.M. 2. Climate –Arid conditions soil has less O.M. –High temperatures decay O.M. more rapidly

August 2008 Factors affecting O.M. 3. Texture –Fine textured soils hold more organic material because clay protects hums from decay

August 2008 Factors affecting O.M 4. Tillage –Prairie will return more than cropping

August 2008 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

August 2008 Functions of O.M. –2. Both humus and O.M. absorb water like a sponge, humus can store 6 times its own weight

August 2008 Functions of O.M. B. Nutrient Availability –Makes several nutrients more available for plant use

August 2008 Functions of O.M C. Soil Aggregation –1. Heavy clay responds best. Breaks down particles, aerates, and makes easier to work with

August 2008 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

August 2008 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

August 2008 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

August 2008 Maintaining Soil O.M. B. Adding fresh organic matter will improve soil the best

August 2008 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

August 2008 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

August 2008 Maintaining Soil O.M. E. Crop Rotation –1. A rotation between row crops, small grains, and legumes is better for keeping high O.M.

August 2008 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.

August 2008 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

August 2008 Maintaining Soil O.M. –4. Horticulture crops are mulched

August 2008 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

August 2008 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

August 2008 Nitrogen Tie-up and Composting –2. They compete with plants for N and can cause slow plant growth

August 2008 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

August 2008 Nitrogen Tie-up and Composting –3. Matter with a low c:n ratio N rich A high c:n ratio is N poor

August 2008 Nitrogen Tie-up and Composting Soil Humus 10 Garden Soil 12 Young Alf 12 compost Rotted manure 20 Clover residue 23 Corn stalks 60 Straw 60 Sawdust 400