Soils unit 3

life in soil

what’s in ¼ teaspoon of soil

50 nematodes, 62000 algae, 72000 amoebas, 111000 fungi, 2920000 actinomycetes, 2528000 bacteria

how many microorganisms per acre

two million tons

carbon cycle

1. CO2 in air is converted to organic carbon

2. photosynthesis converts in into sugar used for energy

3. carbon is stored in cells

4. decomposers release the carbon through decay

organic definition

contains carbon and is or once was alive

photosynthesis equation

6co2 + 6h2o → (light) c6h12o6 + 6o2

relation to soil

soil is a home for organisms that decay stuff, end product is humus (resists decay), releases nutrients stored in plants and animals back into the soil to be reused

producers in soil

autotrophs, plants and a few microorganisms, get food from inorganic carbon

parasites

feed on roots, responsible for plant diseases

predators in soil

prey on other soil life, keep parasite population in check

saprophytes

decompose food on dead OM

soil life 4 categories

bacteria, fungi, algae, and actinomycetes

bacteria

most abundant, one celled, most decompose but some are parasitic or autotrophs

fungi

form threads (hyphae) which form groups called mycelium, fruiting bodies grow and release spores, many decomp. and some are parasites or predators (eat nematodes)

algae

live in water films, most single celled, primary producers with chlorophyl, can form lichen with fungi

actinomycetes

“mold bacteria” can break down resistant material, many produce chemicals to prevent growth of other microorganisms, some antibodies derived can protect plant roots or harm them

rhizosphere

area around plant roots where there is high biological activity

distribution of soil life

most in top 2ft of soil because they need water air and food, most stay near plant roots

the spheres

biosphere- soil life, lithosphere- minerals, hydrosphere- water, atmosphere- air

nutrient cycling

plants can only use the mineral form of nutrients, not anything tied into living organisms or freshly dead OM, animals can use organic or inorganic

mineralization

process of converting an organic nutrient to an inorganic one

immobilization

converting inorganic nutrient to an organic one

nitrogen plant nutrient

34,500 in atmosphere over every acre, not useful to plants in air but certain algae and actinomycetes can use it

nitrogen fixation

N2 → NH4+ (ammonia) plants use nitrogen in ammonia or nitrate (NO3-) form, some plants host bacteria that can fix nitrogen in a symbiotic relationship (bacteria get food home and minerals and the plant gets excess nitrogen)

rhizobium

most important bacteria in crop production, can add up to 300 lbs. of nitrogen per acre per year, symbiotic with legumes (soybeans, peas, peanuts) non crop plants can also use them to fix nitrogen (clover, alfalfa, locust trees, alders, blue green algae) alders can be used to reclaim lands

nitrogen amount needed for crops

1 lb for one bushel of corn, 5 lb for one bushel of soybeans

nitrification equation

NH4+ → NO2 → NO3-

nitrification information

soil cannot be fully saturated as the process requires oxygen, hydrogen replaced with oxygen

nitrosomonas

H leaves the nitrogen and O takes its place

nitrobactar

more oxygen joins to nitrate

denitrification equation

NO3- → NO2 → N2O, NO, N

denitrification information

occurs as various microorganisms steal oxygen to survive in anaerobic conditions (when the soil is saturated)

microbes and soil structure

fungi and actinomycetes have thread like hyphae that hold soil particles together to form a loose aggregate, secretions of other microbes act as a glue that holds particles together, resist falling apart during rain and tillage

mycorrhizae

fungi that form symbiotic relationships with plant roots, M’s get food nutrients and a home and the plants get better ability to absorb; phosphorus, zinc, copper and water, some also protect plant roots against diseases

other benefits of soil microbes

breakdown chemicals, produce organic acids that make nutrients more available to plants (kelation), make vitamins and hormones that improve plant growth, suppress the growth of harmful parasites (antagonism)

inoculation

purposefully infecting a soil with helpful organisms, provide good soil conditions, constant supply of fresh organic matter, aeration, adequate moisture, good soil temp (77 to 99), near neutral pH, good fertility levels

controlling harmful organisms

chemicals (methyl bromide), use disease free seed and plants, dont drag in infected soil, use certified seed, control pH, quarantine, crop rotation, incorporate residue, plant plants that repel certain organisms

allelopathy

plants producing a substance that inhibits the growth of other organisms (cereal rye to corn and marigolds to nematodes)

nematodes

most saprobic, microscopic eel like worms, many are parasites and attack roots to suck nutrients from plants, creates entry points for diseases

soil microfauna

cant be seen with the naked eye

athropods

hard body with jointed legs, insects, many eat decaying OM, other bugs, or plant roots, ants and termites along with others create tunnels that improve aeration and drainage

earthworms

feed on intact organic matter and excrete it as casts which make nutrients more available to plants and hold lots of water, greatly improve soil infiltration and improve soil structure

soil mesofauna

soil organisms that can be seen with the naked eye but are still small

soil macrofauna

mammals

mammals in soil

gophers, rodents, prairie dogs, beneficial due to burrowing, mix the subsoil with topsoil which counters the ageing process by interfering with clay leaching

micro vs macro flora

microflora is unicellular and macro is multicellular

organic matter in soil

the portion of soil that includes animal and plant remains in various stages of decomposition, made up of many complex carbon containing compounds

carbohydrates

long chains of simple sugars- include; starches- food we get from plants, cellulose- long fibers in plant tissue, break down quickly into CO2 and H2O

Lignin

makes plants more stiff, binding agent holding cellulose fiber together, 10-30% of plants tissue, resists breakdown and accounts for much of soil humus

proteins

resist breakdown, long chains of nitrogen containing compounds called amino acids (short carbon chains with N and sometimes sulfur atoms) residue from protein degradation becomes a part of humus and supplies nitrogen

decomposition process

soil flora digest organic compounds releasing CO2 and H2O, carbs are the first to be consumed and simple compounds react further to from humus, lignin remains but changes slightly to form humus, humus itself decays at a very slow rate

humus characteristics

amorphus (no uniform molecular shape) composed of 50% carbon, 5% nitrogen and 0.5% phosphorous along with many other plant nutrients and elements

4 major of humus accumulation

vegetation, climate, soil texture and tillage