Unit 7: Organism & Organic Residues Chapter 5. Objectives Understanding of beneficial & nonbeneficial roles of soil animals Impact of photosynthetic organisms.

Unit 7: Organism & Organic Residues

Chapter 5

Objectives

Understanding of beneficial & nonbeneficial roles of soil animals

Impact of photosynthetic organisms Knowledge of the role of bacteria in the soil Identification of the conditions in which

microbe growth is maximized/decreased Enzymatic role in decomposition Appreciation for role of soil organic matter in

soil chemical & physical properties Value of manure, crop residue, compost,

sewage

Introduction

Weight of bacteria in an acre of soil = 1500+ lbs.

Microbes – mix, aerate soil, fix atmospheric N, decompose organic substances, recycle nutrients

Two most important processes on earth Decomposition Photosynthesis

Animalia: Rodents, Worms, & Insects

Large, burrowing animals to mites

Earthworms major contributor to soil biomass Most biomass comes from soil bacteria & fungi

Burrowing Animals Aerate the soil Alter its fertility & structure Also eat & destroy vegetation Can be more detrimental than beneficial


Earthworms Feed on animal/plant residues

Excretions are small, granular aggregates w/ readily available plant nutrients

Aerate/stir the soil Increases water infiltration Improves root penetration

Borrowing depth Some as deep as 20’ Most in the common root zone (6.6’)


Prefer moist, well-aerated soils (70° F), w/ pH 5.0-8.4

Plenty of materials to eat Low salt concentrations High available Ca Deep soil w/ medium to fine texture Undisturbed by tillage

Hindrances of earthworms Farm machinery Sandy, salty, arid, acidic soils Cold Barren soils


Mice, mites, moles, millipedes, insecticides

Arthropods & Gastropods Arthropods – joint-footed invertebrate

organisms Mites, spiders, scorpions, millipedes, centipedes,

ants, termites, etc. Feed on decaying plant vegetation Aerate soil Can be pests feeding on living plant materials


Gastropods Slugs, snails Feed on decaying vegetation Can eat/damage living plants

Nematodes Microscopic, unsegmented, threadlike worms Omnivorous nematodes – feed on decaying

organic matter, most common soil nematode Predaceous nematodes – prey on soil

bacteria, fungi, algae, other nematodes


Parasitic nematodes – infest plant roots Nearly all field, vegetable crops & trees are

affected How do they cause damage? What other problems can they introduce?

Very hardy Extremely difficult to control Also very expensive Must use resistant varieties, more natural control

means

Plantae: Plants

Play the most important role in the cycle of lifeMost root systems account for 30-50% of the

total plant massRange from older/thicker roots, to single-celled

root hairs Which are most active? Which absorb nutrients? Secrete important materials into the soil that

can be used by other organisms for food, or provides protection from disease

Plantae: Plants

Area around roots is very important to organisms & usually contains highest percentage of microbes = rhizosphere Rhizosphere soil may be quite different than

the soil mass Different proportions of soil nutrients Different soil pH

Fungi: Molds, Mushrooms, Mycorrhizae

Fungi – can’t use sun for energy…live off of live/dead plant/animal tissue Unicellular yeasts Molds Mildews Smuts Rusts Mushrooms


Typically consist of small filaments stretching through the soil

Most important role is as decomposer in the soil

Organic Matter Decomposers First sign of decomposition of organic

materials is presence of filaments (hyphae) Readily attack cellulose

Can compete for soil nutrients Help hold soil aggregates together


w/out fungi, carbon cycle would slow greatly Deleterious Fungi

Predators/parasites on living cells Penetrate other microbes or nematodes &

digest Cause plant diseases

Smut Rust Wilt Powdery mildew, etc.


Cause molds (Aspergillus) growing on grains/peanuts

Produces aflatoxins Very potent and poisonous

Mycorrhizae Fungus root Mutualistic relationship between fungus &

plant roots Symbiosis Share nutrients & water back & forth w/ plant

roots Can extend root’s reach 100x


Particularly helpful in absorbing more nutrients that aren’t as mobile (P, Zn, N, etc.)

Increase drought tolerance of the plant, disease resistance, extreme soil acidity

Can have endo- or ectomcycorrhizae relationship Nursery soils that are sterilized can be

reinoculated to help develop this relationship

Protista

Algae, protozoa, slime molds Algae photosynthesize

Not important decomposers Producers of:

Polysaccharides Oils Other organic substances

Algae inhabit only surface areas of soils In fertile soils, can produce hundreds of kg of organic

material/yr

Protista

Protozoa Unicellular organism, w/out cell wall Ingest bacteria, fungi, other microbes,

nematodes, etc. Numerous in the soil

Can cause serious disease Influence microbe populations & recycling of plant

nutrients

Monera: Bacteria

Actinomycetes & cyanobacteria Actinomycetes

Source of numerous beneficial antibiotics & important decomposers

Cyanobacteria Tiny prokaryotic bacteria No cell wall Aka – mycoplasma

Monera: Bacteria

Soil Bacteria Most numerous soil microbe

1g soil – 1m bacteria Can survive even most extreme environment Populations can double in 30 min

Some may take hours/days Autotrophic

Manufacture their food by synthesis of inorganic materials

Get C from CO2

Monera: Bacteria

Can oxidize materials in soils to make them available to plants

Convert ammonium to nitrite them nitrate NH4 can be used by plants

Nitrite is toxic & volatile Nitrate can be absorbed also, but can leach to

water sources

Convert CO to CO2 & methane gas making these gasses much less lethal

Also can reduce toxicity of some materials

Monera: Bacteria

Heterotrophic Get food & energy directly from organic

substances Most soil bacteria are in this group Can be N-fixers or not Account for much decomposition in the soil

Symbiotic Bacteria Also heterotrophic bacteria Fix atmospheric N in plant root nodules

Can you give an example?

Monera: Bacteria

Provide usable N to the plant, plus return excess to the soil

Infect roots hairs of plants & form nodules where bacteria can fix N in an anaerobic environment

Crops can be inoculated to help this relationship develop

Free-Living N2-Fixing Heterotrophic Bacteria Don’t need a host plant Still have a mutual relationship with nearby

plants Populations may be altered due to

presence/absence of O2

Monera: Bacteria

Bacterial Diseases Cause of numerous diseases in both plants &

animals Most disease causing bacteria in humans has

little to do w/ soil bacteria Blight, wilt, salmonella, etc.

Actinomycetes Small heterotrophic organisms (similar to

fungi) No nucleus

Monera: Bacteria

Many antibiotics have origins w/ this bacteria group

Neomycin, tetracycline, etc. Generally live on dead tissue Important decomposers in the soil

Don’t compete well w/ fungi early in decomposition

Adverse conditions Cold Anaerobic soils Acidic soils

Monera: Bacteria

Very drought tolerant Recently found to have a symbiotic N-fixing

relationship w/ some plant families Prompting research in this area

Soil Viruses & Viroids

Nonliving nucleic acids surrounded by protein coat Can be a replicated protein Do carry genetic material, but only perform

few life functions Prion – various nucleic acids w/out protein

coat – may be most deadly No warning symptoms Difficult to detect

Viroid – no protective coat w/ RNA Virus – protective coat w/ RNA or DNA

Soil Viruses & Viroids

Can cause many plant diseases Control by removing carriers of viruses Enzymes in soil help decompose viruses

Most viruses can only over winter if inside a host

Otherwise will survive only 1-4 wks Over wintering can inoculate the following crop

No chemical control for field virus infections

Conditions for Microbial Activity

Constant competition among microbes for food sources

Depend greatly on: temp, moisture, soil acidity, soil nutrient levels, competition, air

Ideal temp for maximum microbe growth w/ near neutral pH - 86°


Optimum Soil Water & pH for Soil Microbes Water content near/just greater than field

capacity is best (wet, but well aerated) Dryness is often lethal, or they go dormant Anaerobic bacteria thrive in saturated conditions

Prefer soil pH close to 7.0 Most don’t like pH <5.0 Lower the pH, more thrifty fungi


Optimum Temp & Other Conditions for Microbes Activity accelerates as temp increases

Microbes nearly dormant at freezing Activity rate almost doubles from 50° to 68°F

Some strains thrive at low temps, or high temps High nutritive demand

Especially N, P, S, Ca Competition helps to maintain a healthy

population of microbes in the soil As long as soil remains healthy & well managed


Encouraging Beneficial Organisms Very difficult to regulate/manipulate soil

microbe populations Response to changes in environment can

cause quick changes in microbe populations Typically, conditions for good plant growth

also good for microbe growth Ways to encourage desirable microbe

population Inoculate the soil w/ desired microbes, especially

in a soil where a host plant hasn’t grown prior


Lime the soil (keep pH >6.0) Minimize fumigation/sterilization of soil

Kills harmful & beneficial microbes Keep organic matter content high Avoid contamination from problem soils Avoid causing stress conditions

Drought High salt content Water logging Excessive fertilizer

Reduced tillage


Controlling Harmful Microbes Can inject poisonous gasses into soil

Methyl Bromide Used in greenhouses to ensure pest control

Also kills helpful organisms Should be used only in desperate situations Other methods of control

Introduce natural enemies Change soil conditions in favor of different

microbial growth


BMP’s Start w/ disease-free plants & use resistant

varieties Pay attention to sanitation

Can spread easily from equipment, clothes, rodents, etc.

Minimize mechanical injury to plants Control water

Excessive irrigation invites diseases Improve ventilation

Control soil pH Control any infestations quickly

Composition of Organic Matter

Composed of 45-50% Carbon Lesser amounts of H, O, N, P, S, etc. Most are long C chains w/ different

arrangements of organic materials Proteins Lignin's CHO’s Oils Fats Waxes Etc.

Composition of Organic Matter

Humus – substances remaining after chemical/biological breakdown of fresh plant/animal residues & microbial biomass

Most soluble organic matter in form of humic acid or fulvic acid

Other specific organic substances: Sugar amines Nucleic acids Lipids Polysaccharides

Chains of sugar molecules that help hold soil aggregates together

Decomposition of Organic Matter

Energy from sun is released when materials decompose Activation energy must first be obtained before

decomposition can occur (enough heat to start the fire)

Enzymes help reduce activation energy in soils

Enzymes & Biological Reactions Enzyme – lowers activation energy enough to

allow the breaking or formation of a particular bond in nature


These enzyme-influenced reactions = biological reactions

Helps split bonds and open up substances Enzyme is not destroyed/altered in the process

Do decompose, denature over time due to other substances in the soil

Products of Decomposition End products of decomposition (in well

aerated soils) Carbon dioxide Ammonium Nitrate Phosphate


Sulfate Water Other

Can be significantly different under anaerobic conditions

Factors Affecting Decomposition Decomposition rate directly affected by

number of microbes present Absorb nutrients produced & use for growth &

reproduction (N & C)


N is key, as bacteria need it to drive decomposition

C:N Ratio – ratio of carbon:nitrogen in the soil High C:N – low N content, low C:N – high N content

Alfalfa residue – 13:1 Soil microbes – 10:1 Straw – 80:1 Sawdust – 500:1

Affects rate of microbe growth, therefore, speed of decomposition

Plants growing in high C:N ratio soils often N deficient because microbes use N to help w/ decomposition before the plant can use for growth


As decomposition occurs, C lost as CO2 to atmosphere, N kept in soil

Easily decomposed residues go first (sugars, cellulose)

Some microbes may die after these are gone & release their N to plants/soil solution

Lignin may take 10 yrs to decompose fully Dense microbe populations in the upper soil

surface Decomposition of plant residues w/ C:N <20:1

occurs quickly & N returned to the soils/plants


Decomposition of plant materials w/ C:N 20-30:1 – enough N for decomposition, not much released for the plant

Residues >30:1 decompose slowly, lack enough N to feed microbes from residue, microbes feed on soil N (robs from plants)

Conditions favoring microbe growth & higher decomposition rates

Temp: moderate/warm temps Water: moist soils Soil texture: soils higher in clays retain more

organic matter, nutrients for use by microbes

Effects of Soil Organic Matter

Benefits of Soil Organic Matter Source of all soil N not treated w/ mineral

fertilizer Major source of available P & S Supplies major soil aggregate forming

cements Contributes to CEC (usually 30-70% of total

soil CEC) Increases available water content at field

capacity, increases air/water flow


Chelate minerals to help protect them in the soil

C supply for many microbes Reduce erosion, shade soil, moderate soil

temps Buffers soil from acidity or toxicity Leaving mulch on soil surface increases water

infiltration, decreases soil erosion, stabilizes temp changes


Organic Matter as a Source of Nutrients Depends on whether the nutrients can be

supplied at the right time to the plants As temps, decomposition rates, and plant

growth increases, more nutrients become available

Nutrients supplied depends on: Kind of organic matter Soil texture Crop needs


No single soil condition can supply all/optimum nutrients

That’s why we still have to fertilize

Conservation of soil nutrients Protects nutrients from leaching losses Store for future use

Continual release of nutrients As material decomposes, microbes die more

nutrients are mineralized and become available to the plant


Must be careful not to add too much organic matter to the soil

Nitrate pollution of groundwater Phosphate pollution of surface water

Allelopathy – beneficial or harmful effect of chemicals produced by one plant on another plant These toxins in the form of phytotoxins Alfalfa on alfalfa Wheat on barley seedlings


Can help w/ natural weed suppression Some suspect that weeds have an advantage

in this way over crops Maintenance of Soil Organic Matter

Wide ranges of organic matter contents exist, due to climate

Uncultivated soils are highest in organic matter

Plants can grow in soils w/ no organic matter A single amount is not recommended


Usually, organic matter increases, helps plant growth

Can be costly to increase (if you’re buying it, or taking out of production to do so)

Utilize all available residues

Organic Waste Materials

Animal Manure Safe, environmentally friendly disposal is key Best when added to soil, nutrients are

recycled Great fertilizer Good soil conditioner How are we going to deal with the

environmental concerns?


Manure Composition & Use Cattle manure – 3% N, .8% P, 2% K, 25%

organic carbon Manures supply relatively low quantities of

nutrients/unit dry wt. Micronutrient content higher Varies due to the feeding program & livestock Potential problems:

High soluble salts May be high in weed seeds


Sewage Sludge Solids settled from sewage treatment plants Widely usable 4% N, 2% P, .4% K Problems:

May contain toxic elements & heavy metals Can be toxic to plants, animals, people

Some pathogenic organisms can remain present Cholera, diarrhea, hepatitis, tapeworms, etc.


Composting Usually don’t occur naturally

Must have a pile of organic materials Don’t commonly supply a lot of available

nutrients <2% N, P, K

Fresh materials: manure, vegetable wastes – don’t have to be composted – will decompose quickly

Materials w/ high C:N – composting will greatly improve their effectiveness when added to soils


Requires conditions favorable for microbe growth

Best if it is aerobic Temps should reach ~160° F for > 1hr to help

destroy pathogens Compost should be turned regularly Monitor compost moisture level to increase

effectiveness of compost Can kill weed seeds if conditions are right Usually requires several weeks of composting


Can finish compost in ~1 mo or >6 mos, depending on what is composting & how it’s managed

Assignment

Unit 7: Organism & Organic Residues Chapter 5. Objectives Understanding of beneficial & nonbeneficial roles of soil animals Impact of photosynthetic organisms.

Documents

soil identification

soil bacteria fungi

rhizosphere rhizosphere

role of soil organic

beneficial slide

sewage slide

disease slide

insects earthworms feed