Biological Properties of soil Flashcards
Soil Biomass
The total mass of living organisms in the soil
Soil Biomass
The total mass of living organisms in the soil
Humus
The plant and animal material which has been decomposed.
Humification
The process by which soil organic matter is converted to humus.
Microbiome
A community of microorganisms (e.g. bacteria and fungi) that inhabit a particular environment.
Symbiotic relationship
Where different species of living organisms live in a close relationship and both
organisms benefits.
Rhizosphere
The rhizosphere is the area around the roots of a plant occupied by unique microorganisms influenced by the chemicals released from plant roots.
Endorhizosphere
Area of the cortex and endodermis of root where microorganisms can occupy spaces between cells and makes use of nutrients by roots
Rhizoplane
The external surface of the roots and adhering soil particles.
Ectorhizosphere
The area of the rhizosphere which extends from the rhizosphere to the bulk soil.
Calculating soil organic carbon
(SOC)
% SOC = mass of soil organic matter (SOM) X 0.58
Carbon Cycle (KNOW DIAGRAM)
Is the way carbon is used, reused and recycled in nature by living organisms converting it from carbon dioxide (photosynthesis) to carbohydrate and in the soil to carbonate ions.
Nitrogen Cycle (KNOW DIAGRAM)
Is the way nitrogen is recycled in nature, being converted from atmospheric nitrogen to ammonia and then to nitrates and nitrites before being converted back into nitrogen gas.
Nitrogen fixation
Is the process by which nitrogen gas is converted into nitrates which can be used by plants.
Nitrification
Conversion of ammonia or ammonium compounds into nitrite or nitrate
Denitrification
Nitrates are converted to nitrogen gas and nitrogen oxide
Macro-organisms
Organisms that can be seen by the naked eye. E.g. earthworms
Microbiome
A community of microorganism (Bacteria & Fungi) that inhabit a particular environment.
Mineralization
Process in which carbon (C) and nutrients are transformed to CO2 and plant-available forms of nitrogen (N), Phosphorus (P), and sulphur (S).
Bacteria
- Single celled organisms,
- Bacteria in the soil are responsible for fixing nutrients into forms that can be absorbed by plants (e.g. nitrogen and phosphorus)
- Bacteria in the soils also act as decomposers, breaking down organic matter in humus. This recycles nutrients so they can be absorbed by plants.
Fungi
- Fungi in soil act as decomposers, breaking down organic material in humus. This recycles nutrient so they can be absorbed by plants.
- Range from microscopic in size to large mushrooms.
- Responsible for humification of soil organic matter.
- Some fungi form symbiotic relationship with other living organisms.
- Some fungi are parasitic and can damage crops.
parasite
A parasite is an organism that lives on another organism (called a host) causing it harm
EG.) Liver-fluke on sheep
what happens in the rhizosphere
-As plants grow, they release amino acids and sugars into the soil.
- These compounds provide a nutrient supply for the soil micro-organisms.
- This results in a high concentration of microbial activity in the rhizosphere.
- The bacteria and fungi in the rhizosphere create a nutrient rich zone around the roots.
- Symbiotic relationship
- The fungus benefits from the energy produced by the plant, and the plant benefits from mineral nutrients and water supplied by the fungus
Mycorrhiza fungi
- Found in symbiotic relationship within the roots of plants.
- They increase the surface area of the roots for absorption and help dissolve nutrients so they can be absorbed by plants.
- They also enhance the water-holding capacity of the soil and helps bind soil particles together.
-The presence of these fungi increase productivity of crops by improving nutrient uptake.
Earthworms
-One of the most important macro-organisms for the soil.
- Prefer pH 7 , and warm and moist soils <12C
Benefits of earthworms
-Improves nutrient availability by breaking down organic material to humus which has more nutrients that can be taken up by plants.
- Improve soil structure by creating stable aggregates.
- Burrow, creating channels that improve aeration and drainage.
- Overall productivity is improved, minimum cultivation improves earthworms populations as ploughing reduces their population.
Organic matter & benefits
Formed when organic material is broken down by decomposers into a stable state. This decomposed organic matter can also be called humus.
- Avg. soils have 5% OM
1. Provides nutrients to the soil
2. Increases water retaining capabilities
3. Improves soil structure by contributing to aggregate formation.
4. Helps prevent soil erosion
Large VS small particles of OM
Large particles :
Improve drainage & do not contribute to ion exchange
Small Particles:
Source of nutrients for plant growth
important in ion exchange.
How to increase OM in soils
-Minimum cultivation and No-till practices encourage the building-up of organic matter.
-Cover crops can reduce soil erosion and so help maintain the organic matter in topsoil
- Soils with high OM have more stable aggregates
- Aggregates can be broken down with rainfall if they have low OM
Function of Soil Organic matter
BIOLOGICAL:
Nutrient reservoir - Humus stores carbon and other mineral nutrients.
Biodiversity - Provides nutrients and energy for macro and micro-organisms.
CHEMICAL:
- Soil pH buffer - Keeps pH at optimum levels for plants and organisms
- Cation exchange - Humus = increase in cation exchange.
Nutrient Supply - N & P can be released from soil OM
PHYSICAL:
- Soil structure - aggregation
- Water retention- OM has a high ability to absorb and retain water.
- Reduction of soil capping
- Reduction/Prevention of soil erosion
-Reduction of soil compaction
Methods of proving Soil OM
- Catch crops
- Crop roatation
- FYM/ Organic fertilisers
- Straw
- Min TILL
- Return to permanent pasture
Nitrogen cycle (detailed)
- Nitrogen moves through the atmosphere , soil, plants and animals in a cycle.
- The nitrogen cycle is the way nitrogen is recycled in nature, being converted from atmospheric nitrogen to ammonia and then to nitrites and nitrates before being converted back to nitrogen gas.
- Plants can absorb nitrogen in the form of nitrate ions (NO3-) but they cannot absorb nitrogen in the form of ammonium ions (NH4+) or urea
- Nitrogen fixing bacteria convert atmospheric nitrogen to nitrates. Nitrates can also be directly added to soil by lightening and by artificial fertilisers.
- These nitrates can be taken up by plants and converted to plant proteins, these are then consumed by animals which convert them to animal proteins.
- When animals die or produce waste, decomposers produce ammonia from the animal protein that they break down.
- Nitrosomonas bacteria convert this ammonia to nitrites and Nitrobacter bacteria convert the nitrites to nitrates.
- This process is called nitrification
- If there is a surplus of nitrates in the soil, denitrifying bacteria will convert the nitrates back into nitrogen gas. This process is called Denitrification.
Carbon Cycle (know Diagram) Role of organisms
PLANTS: remove the carbon from the air through photosynthesis., This carbon is consumed by animals when they feed on plants.
PLANTS & ANIMALS: produce carbon dioxide during respiration which returns to the atmosphere.
MICRO-ORGANISMS: When living things die and decay, carbon dioxide is produced by decomposers which returns to the air. The remaining carbon is stored in humus in the soil.
RUMINANTS: produce methane (CH4) during digestion which is released into the atmosphere.
- Over millions of years, dead plants and animals have built up to form fossil fuels underground, this acts as a carbon store.
-The combustion of these fossil fuels produces carbon dioxide which contributes to the levels in the air.
Carbon sequestration
The long term capture of carbon dioxide from the atmosphere
Carbon source
If carbon levels in soil are decreasing because the output of carbon is lower than the inputs, but is considered a carbon source.
Carbon sink
Carbon levels in soils are increasing because output is lower than input = carbon sink
input = output soil, Carbon is in a steady state
Management to maintain soil carbon levels
- Reducing deforestation
- Afforestation
- Min/no-till practices
- Use FYM
Rhizobium and clover
- Some bacteria are extremely beneficial in agriculture
- Rhizobium is a rod-shaped bacteria that has a symbiotic relationship relationship with clover.
- Live in the roots nodules of clover plants.
- Rhizobium changes atmospheric nitrogen into nitrates, which can be used by the plant.
Rhizobium and clover
- Some bacteria are extremely beneficial in agriculture
- Rhizobium is a rod-shaped bacteria that has a symbiotic relationship relationship with clover.
- Live in the roots nodules of clover plants.
- Rhizobium changes atmospheric nitrogen into nitrates, which can be used by the plant.
