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Biology > Soils and Plant Nutrients > Flashcards

Soils and Plant Nutrients Flashcards

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1
Q

Give a summary of soil

A
  • Soil contains a living, complex ecosystem
    » Living organisms play an important role in these soil layers
  • Plants obtain most of their water and minerals from the upper layers of soil
  • This complex ecosystem is fragile, takes centuries to form but can be destroyed by human mismanagement in just a few years
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2
Q

What are the basic properties of soil?

A

» Texture

» Composition

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3
Q

How is the soil separated into layers?

A
  • Soil is stratified into layers called soil horizons
    » A horizon = “topsoil”
    » B horizon contains less organic matter and is less weathered
    » C horizon composed of partially broken-down rocks
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4
Q

What is topsoil?

A
  • “A horizon”

- Topsoil consists of mineral particles, living organisms, and humus (decaying organic material)

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5
Q

What determines soil texture?

A
  • Texture determined in part by the size of inorganic soil particles which affect soil characteristics
  • Soil is usually a mix of the three
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6
Q

What are the inorganic soil particles which affect soil characteristics

A

» Sand: largest particles (0.05 – 2 mm) → larger space b/w particles → well oxygenated, but does not retain water
» Clay soil: small particles (<0.002 mm) → particles tightly packed → poor oxygen, but good water retention
» Silt: in between (particles 0.002 – 0.05 mm)

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7
Q

What is soil solution?

A
  • Soil solution consists of water and dissolved minerals in the pores between soil particles
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8
Q

What happens to water in soil?

A
  • After a heavy rainfall, water drains from the larger spaces in the soil, but smaller spaces retain water because it is attracted to negatively charged surfaces of clay and other particles
  • The film of loosely bound water is available to plants
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9
Q

What are Loams?

A
  • Loams are the most fertile topsoils and contain equal amounts of sand, silt, and clay
    » Good balance between aeration, drainage and water storage capacity
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10
Q

What does soil composition mean?

A
  • A soil’s composition refers to its inorganic (mineral) and organic chemical components
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11
Q

What is the first type of inorganic components of soil?

A
  • Clay particles in productive soils are negatively charged
  • Some nutrients are negatively charged ions (“anions”, such as phosphate H2PO4- , nitrate NO3- and sulphate SO4 2- ); they do not bind with soil particles and can be lost from the soil by leaching when water percolates through the soil
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12
Q

What is the 2nd type of inorganic components of soil?

A
  • Clay particles in productive soils are negatively charged
  • Positively charged ions (“cations”, such as potassium K+, calcium Ca2+ and magnesium Mg2+) adhere to negatively charged soil particles; this prevents them from leaching out
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13
Q

How do cations such as potassium enter the plants?

A
  • During cation exchange, cations are displaced from soil particles by other cations (eg, H+) → displaced cations enter the soil solution and can be taken up by plant roots
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14
Q

What is the first step of Cation exchange in soil?

A
  • Roots acidify the soil solution by releasing CO2 from respiration and pumping H+ into the soil.
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15
Q

What is the second step of Cation Exchange in soil?

A
  • CO2 reacts with H2O to form H2CO3, Which releases H+ upon disassociation
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16
Q

What is step 3 of Cation Exchange in soil?

A
  • H+ ions in the soil solution neutralise the negative charge of soil particles, causing the release of mineral cations into the soil solution.
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17
Q

What is step 4 of Cation Exchange in soil.

A
  • Roots absorb the released cations
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18
Q

What is the main organic compound in soil?

A
  • Humus (organic material from decomposition of fallen leaves, dead organisms, faeces and other organic material from bacteria and fungi) builds crumbly soil that retains water but is still porous
  • It also increases the soil’s capacity to exchange cations and serves as a reservoir of mineral nutrients
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19
Q

What else is in the topsoil that is beneficial to other plants? Why?

A
  • Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots
  • These organisms help to decompose organic material and mix the soil
20
Q

Why are living organisms important in soil?

A
  • A variety of living organisms inhabit the soil and are important for recycling of nutrients
  • They include:
    » Beetles, termites, millipedes, ants and cockroaches
    » Slugs, snails, earthworms, fungus(mushrooms) and soil fungi (the parts below the mushrooms)
    » Spiders, slaters, cicada nymphs and pseudoscorpions
    » nematodes and soil protozoans
21
Q

What is Australian soil like?

A
  • Old continent
  • Soils are heavily leached often with low levels of nutrients - farming and grazing have added to problem
  • Australia soils: not a lot of A and B horizon, not much humus in soils, lots of nutrients leached out over long time
22
Q

How many classes of soils are in Australia?

A
  • 14 different classes of soils in Aus

- Range of other soil types in local area

23
Q

What are the most common soil types in QLD?

A

» Vertosols: abundant clay texture; floodplains; shrink and crack when dry, expand when wet → cracking
» Kandosols: rich in quartz; little texture and weak B horizon; abundant clay texture

24
Q

What effect has land use and farming had on Australian soil?

A
  • Land use influences structure, nutrient status, and salinity of soils
  • Farming practices of the colonists that were not suited to Australian conditions had significant environmental impact
  • Grazing and tilling broke up the delicate mat of algae and lichen that held the topsoil together
25
Q

What impact does erosion have of soil?

A
  • Topsoil from thousands of acres of farmland is lost to water and wind erosion each year
  • Erosion of soil causes loss of nutrients
26
Q

What is salinisation?

A
  • The replacement of deep rooted native plants with shallow-rooted crops has led to the loss of productive land to salinity
  • This means that as the rain falls, less of it is being absorbed and so the water table under the soil rises and pushes the salt to the surface of the soil
27
Q

Water, air and soil all contribute to plant growth, how do they do this and what happens if they are not there?

A

» Carbon and oxygen come from the atmosphere; nitrogen comes from the atmosphere (N-fixing symbiont)
» Water comes from the ground
» Other mineral nutrients originate mostly from weathering of soil and rock
- Lack of nutrients hinders plant growth and reproduction

28
Q

What are macro-nutrients?

A
  • Macronutrients are essential elements plants need in relatively large quantities
29
Q

Why are macronutreints important?

A
  • Major components of organic compounds that form the plant’s structure: carbon, oxygen, hydrogen, nitrogen, phosphorous and sulphur
    • Nitrogen contributes the most to plant growth and crop yield, as it is a required component of proteins, nucleic acids, chlorophyll and other important organic compounds
  • Inorganic catalysts needed to facilitate biochemical reactions: potassium,
    calcium and magnesium
30
Q

What are Micronutrients?

A
  • Micronutrients are essential elements needed in relatively small amounts:
    » Chlorine, iron, manganese, boron, zinc, copper, nickel and molybdenum
    » Often act as cofactors (nonprotein helpers in enzymatic reactions)
31
Q

What are Symptoms of deficiency and how do they work?

A
  • When a plant is lacking in a certain mineral or nutrients they will display different signals which shows that they are deficient in something
  • Symptoms of deficiency depend on the mineral’s function
    » Macronutrient deficiency more common than micronutrient deficiency
32
Q

provide an example of symptoms of deficiency

A
  • In corn plants, the leaves will start to go brown from the tips and down the center of the plant if it is deficient in nitrogen.
  • Similarly it will demonstrate a purple colour on the edges of its leaves if it is lacking in phosphorus.
33
Q

What are some of the benefits of soil in relation to plants?

A
  • Nutrient absorption
  • Anchorage and stability
    » Grow to great heights
    » Withstand wind, storms, etc
  • Presence of mutualistic symbionts:
    » Bacteria and fungi provide mineral nutrients and fixed nitrogen
    » Some fungi form mycorrhizal associations, increasing the surface area through which plants absorb water and minerals
34
Q

What is the mutualistic relationship plants have with microorganisms?

A
  • Mutualistic relationship between plants and microorganisms
    » Plants provide microorganisms with photosynthetic products for energy and as a carbon source
    » Microorganisms provide plants with mineral nutrients and fixed nitrogen
35
Q

What is the relationship between plants and fungi and how does the plants nutrition benefit from fungi?

A
  • Mycorrhizae are mutualistic associations of fungi and roots
  • The fungus benefits from a steady supply of sugar from the host plant
  • The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption
  • Mycorrhizal fungi also secrete growth factors that stimulate root growth and branching
36
Q

What is a root nodule?

A
  • A swelling on a root of a leguminous plant, containing nitrogen-fixing bacteria.
37
Q

What is the relationship between bacteria and nodules?

A
  • Bacteria in root nodules help legumes by fixing nitrogen in exchange for “a place to live” and food (sugars)
38
Q

draw the role of soil bacteria in nitrogen nutrients diagram

A

Google doc

https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing

39
Q

What is the main form of soil management that is assisting in sustainable agriculture?

A
  • Soil management by fertilisation and other practices helped establish modern societies
40
Q

Why is irrigation unsustainable

A
  • Irrigation is a huge drain on water resources when used for farming in arid regions
    » 75% of global freshwater use is devoted to agriculture
    » Agriculture = 62% of Australia’s water consumption, most used for irrigation (cotton growing = 17%)
41
Q

What effects does irrigation have on the land?

A
  • The primary source of irrigation water is underground water reserves called aquifers
  • The depleting of aquifers can result in land subsidence, the settling or sinking of land
  • Irrigation can also lead to salinisation, the concentration of salts in soil as water evaporates
  • Drip irrigation requires less water and reduces salinisation
42
Q

Why is fertilisation important?

A
  • Soils can become depleted of nutrients as plants and the nutrients they contain are harvested
  • Fertilisation replaces mineral nutrients that have been lost from the soil
43
Q

What are commercial fertilisers?

A
  • Commercial fertilisers are enriched in nitrogen (N), phosphorus (P), and potassium (K)
    » Excess minerals (especially anions like N and P) are often leached from the soil and can cause algal blooms in lakes
44
Q

What are Organic fertilisers?

A
  • Organic fertilisers are composed of manure, fishmeal, or compost
    » They release N, P, and K slowly as they decompose
45
Q

Why is soil pH important?

A
  • Soil pH affects cation exchange and the chemical form of minerals
  • Cations are more available in slightly acidic soil, as H+ ions displace mineral cations from clay particles
  • The availability of different minerals varies with pH
    » For example, at pH 8 plants can absorb calcium but not iron
46
Q

How can erosion be controlled and why must it be controlled?

A
  • Considerable amounts of topsoil are lost to water and wind erosion
  • Erosion of soil causes loss of nutrients
  • Erosion can be reduced by
    » Planting trees (windbreaker, root stabilisation)
    » Terracing hillside crops
    » Cultivating in a contour pattern
    » Practicing no-till agriculture (growing crops from year to year without disturbing the soil through tillage) completely eliminates soil erosion

Biology (27 decks)

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