CSS 200 – SOILS and PLANT NUTRITION - NOTES
WEEK #4
LIFE in the SOIL
ORGANIC MATTER
REVIEW – MIDTERM EXAM today
LIFE in the SOIL – SOIL BIOLOGY
There are a DIVERSITY of ORGANISMS in SOIL and MANY
WAYS to CLASSIFY THEM
 SIZE
o MICROORGANISMS – invisible to eye
o MACROORGANISMS – visible to eye
 What they EAT or PRODUCE
o PRODUCERS – an organism that does
PHOTOSYNTHESIS
o HERBIVORES – eats PLANTS
o PREDATORS – eats ANIMALS
o PARASITES – FEEDS on PLANTS or ANIMALS
o DECOMPOSERS – eats DEAD OM, SAPROPHYTES
 PREFERRED ENVIRONMENT
o AEROBIC - Needs O2 to live
o ANAEROBIC - Can live without O2
 Waterlogged and poorly drained soils
CYCLES and WEBS
 CYCLES look at NUTRIENT RECYCLING
o CYCLES – Carbon (show overhead)
 If all we have is PRODUCERS, HERBIVORES,
PREDATORS, and PARASITES the C CYCLE
would collapse
 We have to have DECOMPOSERS in SOILS to
complete the cycle
 WEBS look at the ORGANISMS involved and their
RELATIONSHIPS with each other (Show overhead)
o Fueled by PRODUCERS that CONVERT
CO2 + SUN ENERGY >>>> ORGANIC C (Photosynthesis)
o Most other ORGANISMS exist by CONSUMING
ORGANIC C in PLANTS, ANIMALS, and WASTE
o As they CONSUME they do TWO THINGS:
 CONVERT it to one FORM or ANOTHER of
ORGANIC C
 Or - Make it AVAILABLE to PLANTS as
NUTRIENTS
SOIL ORGANIC MATTER – FOOD for the WEB
ORGANIC MATTER is the portion of soil that contains PLANT
and ANIMAL RESIDUES at various levels of DECAY
 Most OM CHEMICALLY made of COMPLEX Compounds
o CARBOHYDRATES – long chains of simple sugars
 Sugars, Starches, Cellulose
o LIGNINS – secondary cell walls that make cells rigid
 Resist decay
 10-30% of plant material
o PROTEINS – long chains of N containing compounds
(amino acids)
 Also contain S
ORGANIC MATTER DECOMPOSITION
 OM can be divided into 2 groups - ACTIVE OM & HUMUS
 ACTIVE OM - OM EASILY DECOMPOSED by
MICROBES
o It CONSISTS of:
 Plant ROOTS EXUDE (leak) a variety of
ORGANIC COMPOUNDS
 ROOTS also SLOUGH OFF PLANT PARTS
o Root cap cells, root hairs, bark of mature roots
 DEAD OM
o MICROBES use RESPIRATION to break down OM
 OM + O2 >>> CO2 + H2O + HUMUS
 Occurs RAPIDLY – weeks to months
 HUMUS – OM that RESISTS DECAY
o HUMUS is DARK and made of tiny, CLAY sized
particles
o OXIDATION – chemical decomposition of HUMUS
 HUMUS + O2 >>> CO2 + H2O
 Occurs SLOWLY - 1-3% loss of HUMUS / year
NUTRIENT CYCLING of OM
 PLANTS can ONLY USE NUTRIENTS in SIMPLE
INORGANIC IONS
 When NUTRIENTS are TIED UP in the BODIES of living
ORGANISMS or in FRESH OM they cannot be used by
plants
o This is called IMMOBILIZATION
o Keeps NUTRIENTS from LEACHING
 When MICROBES break down COMPLEX ORGANIC
FORMS to SIMPLER INORGANIC FORMS that PLANTS
CAN USE
o This is called MINERALIZATION
o When MICROBES EXCRETE, DIE, or are EATEN by
another ORGANISM they will RELEASE
NUTRIENTS that plants can use
DISTRIBUTION of SOIL BIOLOGY
 Top 2’ of SOIL – O and A Horizons
o Most O2
o Most H2O
o Most OM
o Best SOIL STRUCTURE
 RHIZOSPHERE (Show overhead and handout)
o ½” around each ROOT
o Where LEAKING and SLOUGHING occurs, promotes
high biological activity
o BACTERIAL dominated where SIMPLE SUGARS
 LITTER LAYER (O Horizon) and HUMUS
o FUNGAL dominated where COMPLEX C compounds
 SOIL PORES
o Arthropods, Earthworms in air spaces
o Protozoa and Nematodes in water films
SOIL ORGANISM ACTIVITY (Show overhead and handout)
 DEPENDS on MOISTURE and TEMP
o As MOISTURE increases, ACTIVITY increases
o As TEMPERATURE increases, ACTIVITY increases
 SOME ORGANISM is always ACTIVE
MICROORGANISMS
 BACTERIA
o MOST ABUNDANT inhabitants in soil
o SINGLE CELLED MICROSCOPIC organisms
o Live on soil particles in RHIZOSPHERE
o 4 MAJOR and TWO MINOR TYPES
 DECOMPOSERS – consume SIMPLE C
compounds
 SAPROPHYTIC
 IMMOBILIZE and RETAIN nutrients in
body
 MUTUALISTS – N FIXERS
 BENEFICIAL relationship with PLANTS
 Reside in ROOT NODULES
 Take atmospheric N2 and convert to NH4
 PLANTS get NH4 and BACTERIA get
simple sugars, etc.
Example: Alfalfa and Rhizobium bacteria
 Some N FIXERS are FREE LIVING or
NON-SYMBIOTIC
 PATHOGENS - FEED on plant ROOTS
Example: Xymomonas, Erwinia, Agrobacterium
 CHEMOTROPHS (or LITHOTROPHS)
 FEED on INORGANIC COPOUNDS of N,
S, Fe, or H
 Important to N CYCLE (Show overhead)
 Some good at DEGRADING
POLLUTANTS
 2 ODD BALLS
 PHOTOSYNTHETIC CYANOBACTERIA
o PRODUCERS – photosynthesize
sugars, increase OM insoils
o Live in WATER FILMS
 ACTINOMYCETES
o FILAMENTOUS bacteria
o Give soil EARTHY SMELL
o DEGRADE COMPLEX C compounds
o PRODUCE ANTIBIOTICS that can
inhibit growth of other organisms
o Tolerant of DRY, HIGH TEMP and
HIGH pH soils
o Most are SAPROPHYTIC, some
PARASITIC
Example: Potato Scab – Steptomyces
scabies
o IMPORTANT ROLES of BACTERIA
 IMMOBILIZATION of NUTRIENTS prevents
LEACHING
 Produce GUMS that BIND soil particles and
BUILDS SOIL STRUCTURE
 Some FILTER and DEGRADE POLLUTANTS
 DOMINANT in NEUTRAL pH soils and
GRASSLANDS
 FUNGI
o FEWER numbers of FUNGI in soil, but makes up the
LARGEST MASS in soil
o FILAMENTOUS, MULTI-CELLULAR organisms
 Individual threads called HYPHAE
 Masses of hyphae called MYCELIUM
o 4 TYPES
 DECOMPOSERS – SAPROPHYTIC
 COMPLEX C compounds
 Excrete organic ACIDS which increase
HUMUS
 MUTUALISTS - MYCORRHIZAE
 Fungus – Root, COLONIZE ROOTS of
plants
 HYPHAE SMALLER than ROOT S and
can grow into SMALLER PORES and O
Horizon to find more FOOD
 2 MAJOR TYPES (3 actually)
o ECTOmycorrhizae
 Forms a MANTLE surrounding
ROOT and IN BETWEEN CELLS
 Artificially grown and
INOCULATED
o ENDOmycorrhizae – AM (VAM)
 Grows INTO CELLS of roots and
forms ARBUSCLES (nutrient
transfer), VESCICLES (storage)
 Cannot be artificially grown
o ECENDOmycorrhizae
 Intermediate type seen in nurseries
and after forest fires
 Thin mantle and some cell
penetration, but turns into ECTO
as matures
 Increases ABSORPTION of P, Zn, Cu, H2O
 Some PROTECT PLANT from diseases
causing PATHOGENS due to mantle
 PATHOGENS - DISEASE causing organisms
Examples: Verticillium (wilt), Pythium,
(wilt), Rhizoctonia (damping off)
 PREDATORS
 NEMATODE eating fungi
o IMPORTANT CHARACTERISTICS of FUNGI
 Like O Horizon for COMPLEX C compounds
 AEROBIC soils
 DOMINATE ACID soils, FOREST soils
 DETRIMENTAL HABITATS
 TILLAGE
 FUNGICIDE use
 High N or P FERTILIZER use
 Fallowed FIELDS
 Non-Mycorrhizae CROPS
 PROTOZOA (Kingdom - Protista)
 SINGLE CELLED organisms
 3 TYPES
 CILIATES
 AMOEBA
 FLAGELLATES
 FEED on BACTERIA
 C : N ratio BACTERIA
4 - 5: 1
 C : N ratio PROTOZOA
10 : 1
 As feed on bacteria EXCRETE excess N as
NH4 (mineralization)
MACRO-ORGANISMS
 NEMATODES
o NON – segmented, EEL-LIKE WORMS, 1/20” long
o MULTI-CELLULAR organisms
o PRODUCE EGGS in masses
o 5 TYPES – based on what they FEED on
 BACTERIAL feeders
 FUNGAL feeders – suck out HYPHAE
 PREDATORS – feed on other NEMATODES and
PROTOZOA with a TOOTH
 OMNIVORES – feed on a VARIETY of
organisms with a TOOTH
 Some “Living Insecticides” feed on
INSECT LARVAE
Example: Root weevil nematodes
 PLANT ROOT feeders – PARASITIC
 Puncture roots with STYLET, hollow needle
o Saps ENERGY of PLANT, can cause
WILTING, STUNTING
 Can be ENTRY POINT for other organisms
o IMPORTANT CHARACTERISTICS
 Most common in POROUS SOILS with large
pore spaces and in WATER FILMS
 DISTRIBUTE Bacteria and Fungi throughout
soil within digestive tract and outside of body
 Most USEFUL INDICATOR of a HEALTHY
SOIL FOOD WEB – DIVERSITY
 ARTHROPODS
o MULTI-CELLULAR
o INVERTEBRATES (no skeleton)
 JOINTED LEGS
 EXOSKELETONS
o 4 TYPES
 INSECTS – Springtails, Beetles, Ants
 CRUSTACEANS – Sow bugs
 ARACHNIDS – Spiders, Mites
 MYRAPODS – Centipedes, Millipedes, scorpions
o IMPORTANT CHARACTERISTICS
 Exist in the TOP 3” of SOIL
 SHRED and MIX OM, breaks down faster
 IMPROVES SOIL STRUCTURE by
BURROWING and adding FECAL PELLETS
 EARTHWORMS
o INVERTEBRATES (no skeleton)
o 3 TYPES
 EPIGEIC – LITTER dwellers
 Compost piles - Red Wigglers
 ENDOGEIC - SHALLOW soil (top to 12” down)
 Not permanent burrows
 ANECIC – DEEP BURROWING (to 6” down)
 Night crawlers
 Permanent BURROWS
o IMPORTANT CHARACTERISTICS
 TURN SOIL OVER – top 6” in 10-20 years
 IMPROVE SOIL STRUCTURE with
BURROWS (biopores) and FECAL PELLETS
 Most abundant in LOAM, where MOISTURE,
O2, and NEUTRAL pH
 MAMMALS
o RODENTS
 Gophers, Woodchucks, Prairie Dogs, Moles
o Highest concentration in UNDISTURBED SOILS
 Pasture, Forest, Prairie
o IMPORTANT CHARACTERISTICS
 REJUVENATION of soil by BURROWING and
MIXING SOIL HORIZONS
SUMMARY of the SOIL FOOD WEB
 Researchers have not DEFINED how much or what kind of
DIVERSITY is BEST for the SOIL FOOD WEB
 WHAT WE DO KNOW:
o NUTRIENT CYCLING
 More ORGANISMS – FASTER cycling
o NUTRIENT RETENTION
o IMPROVED STRUCTURE
o DISEASE SUPPRESSION
o DEGRADE POLLUTANTS
o Greater BIODIVERSITY = Greater STABILITY of the
WEB
 WHAT does this mean for LAND MANAGEMENT?
o Less FERTILIZER
o Greater INFILTRATION, less EROSION
o Less PESTICIDES
o Greater WATER QUALITY

RESILIENCE – the ability of the SOIL to RECOVER after
FIRE, COMPACTION, TILLAGE, etc. depends on the
DIVERSITY of BIOLOGY present