Lecture 10 aSoil Organic Matter=SOM Is this a healthy soil? Is this a healthy field?
SOM • Soil Organic matter encompasses all organic components of a soil: • Fresh residues • Decomposing organic matter • Stable organic matter • Living organisms
Soil Organic Matter • Soil organic matter - • all living organisms (microorganisms, earthworms, etc), • fresh residues (old plant roots, crop residues, recently added manures), • well-decomposed residues (humus). • The SOM content of agricultural topsoil is usually in the range of 1 to 6%. • This amount is the result of all additions and losses of SOM that have occurred over the years. Citizen Science – Kansas State
Fresh Residues • Up to 15% of organic matter is fresh residue • Comprised mainly of litter fall • Much can be recognized as plant residue
Decomposing Organic Matter • Plant material is transformed from one organic compound to another mainly by organisms in the soil • Organisms create by-products, wastes, and cell tissue • Compounds released as waste by one organisms can often be used as food by another
Soil Organic Matter =SOM • SOM is labile* -it can decline rapidly if the soil environment changes and renewable -it can be replenished by inputs of organic material to the soil. • * Labile = Constantly or readily undergoing chemical, physical, or biological change or breakdown; unstable.
Adequate levels of SOM can be maintained with: • proper fertilization, • crop rotations, and tillage practices • Returning crop residues to the soil.
Morrow Plots – Why the difference in SOM? Factors Controlling SOM • 1) Kind of parent materials (texture primarily), climate, slope, and management practices that exist. • 2) Climate: PMs that have not lost their nutrients from excessive rainfall (leaching), and areas where temperature and water are adequate will have high SOM. • 3) Management practices that affect crop biomass (yield and straw) production (water, fertilizer, variety), residue maintenance (equipment, harvest), and litter (wind) will also affect SOM content. • 4) As dry matter production increases, SOM increases. • 5) However, only that which remains after harvest along with root biomass will influence long-term SOM content. manure, lime and phosphorus (MLP) Established in 1876 the Morrow Plots are the oldest agronomic experiment fields in the United States. They include the longest-term continuous corn plot in the world. Located near the center of the University of Illinois' Urbana campus.
How is SOM Measured? SOM is usually measured in the laboratory as organic carbon, Soil organic matter is estimated to contain 58% organic carbon (varies from 40 to 58%) with the rest of the SOM comprising of other elements (eg, 5% N, 0.5% P and 0.5% S). A conversion to SOM from a given organic carbon analysis requires that the organic carbon content be multiplied by a factor of 1.72 (1.00/0.58). Thus, 2% SOM is about 1.2% organic carbon. Testing for Soil Organic Carbon UF/IFAS Extension Soil Testing Laboratory
Active Fraction • 10 to 30% of the soil organic matter (active fraction) is responsible for maintaining soil microorganisms. • The active fraction of organic matter is most susceptible to soil management practices. (Inactive = humus) ACTIVE
Adding Fresh OM • In a soil which at first has no readily decomposable materials, adding fresh tissue under favorable conditions: • 1) immediately starts rapid multiplication of bacteria, fungi, and actinomycetes, • 2) which are soon actively decomposing the fresh tissue. ADDED
Fresh SOM • as most readily available energy sources are used up, microorganisms again become relatively inactive, • leaving behind a dark mixture usually referred to as humus – a stable organic compound
Stable Organic Matter -Humus • Thus, soil organic compounds become stabilized and resistant to further changes by microorganisms • Stabilized organic matter acts like a sponge and can absorb six times its weight in water
HUMUS Leaf Humus • Newly-formed humus= • a) combination of resistant materials from the original plant tissue, • b) compounds synthesized as part of the microorganisms' tissue which remain as the organisms die. (Fluvic and Humic Acid) • humus is resistant to further microbial attack- N and P are protected from ready solubility.
Function of Humus • holds water and nutrients; • it sticks together & helps establish and maintain a strong crumb structure & thus reduce soil erosion • it provides some nutrients (N & P) as it is slowly decayed by microbial activity, • Buffers effects of pesticides • humus decomposes at the rate of 2.5% per year • Creates good soil “ Tilth” • Coates the sand, silt, clay particles making them dark and the darker the color, the greater the amount of soil humus present. Humus = High Medium Low
SOM Maintains soil “Tilth” • aiding infiltration of air and water • promoting water retention • reducing erosion BMI
“If your soil clods can't pass the water test, change your management practices. It will help your bottom line as well as the soil.” – Ray Weil – Univ of Maryland SOM = SOIL HEALTH • Measuring SOM is one step in assessing overall soil quality or soil health - • measuring various key attributes of soil organic matter quantity and quality will give an indication of the health of the soil. • Or Look at the state of the soil organisms in the soil. • Or look at how well the soil “Holds Together”. Simple clod test: Healthy soil, at left, holds together in water, while poor soil falls apart.
Use of Soil Quality • 1) Match use and management of land to soil capability, because improper use of a soil can damage it and the ecosystem. • 2) Establish a baseline understanding about soil quality so that we can recognize changes as they develop. • 3) Use baselines to determine if soil quality is deteriorating, stable, or improving. • Thus soil quality becomes a good indicator of the health of an ecosystem. NatureWatch
Soil Quality • Soil quality is the capacity of soils within landscapes to sustain biological productivity, maintain environmental quality, and promote plant and animal health. • Protecting soil quality like protecting air quality and water quality should be fundamental goal of our Nation’s Environmental Policy http://www.directseed.org/soil_quality.htm Poor Good http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14
Cornell researcher George Abawi describes soil health strategies at an Onion Council field day in Wayne County, N.Y.Photo by Carol R. MacNeil. SOIL HEALTH • Soil Health is the change in Soil Quality over time due to human use and management or to natural events. • Descriptive terms for Soil Health • Organic Matter - high • Crop appearance = green, healthy,lush • erosion – Soil will not erode • earthworms – numerous • infiltration – fast, no ponding • Compaction - minimal In Vernon and surrounding counties are the largest concentration of organic farmers in Wisconsin.
Is this a good Idea? • The Grimm Brother's fairy tale, Rumpelstiltskin spins straw into gold. • Thanks to advances in biotechnology, researchers can now transform straw, and other plant wastes, into "green" gold - cellulosic ethanol. • While chemically identical to ethanol produced from corn or soybeans, cellulose ethanol exhibits a net energy content three times higher than corn ethanol and emits a low net level of greenhouse gases. • Recent technological developments are not only improving yields but also driving down production cost, bringing us nearer to the day when cellulosic ethanol could replace expensive, imported "black gold" with a sustainable, domestically produced biofuel. http://www.harvestcleanenergy.org/enews/enews_0505/enews_0505_Cellulosic_Ethanol.htm • WHAT ABOUT SOM?????
The End What is the health of this soil?