W1, Intro + Nutrient movement through soils Flashcards
What’s the mobility and method of movement (% of uptake) for:
Boron (B)
- Mobile
- Mass flow = 65%
- Diffusion = 32%
- Root interception = 3%
Describe the pattern of nutrient uptake for wheat during the growing season.
Explain the differences between the way nutrients can move to the roots (mass flow, diffusion, interception)
MASS FLOW
- nutrients in solution move with that solution
- driven by transpiration
- the greater the transpiration, the greater the movement of water to the root, and therefore the greater the movement of nutrients (because they’re in solution)
- = [concentration in soil solution] * [water transpired]
- e.g.
- water use = 1.5 ML/ha = 1,500,000 L/ha
- [soil solution] = 25 mg/L = 0.000025 kg/L
- plant uptake (required by plant) = 60 kg/ha
- % uptake by mass flow = 0.000025 * 1,500,000 = 37.5 kg/ha = 62.5% uptake
DIFFUSION
- nutrient movement is based on a concentration gradient (i.e. nutients move from a region of [high] to [low]
- the greater the concentration gradient (difference), the faster the movement
- slower than mass flow
- roots will create a depletion zone in/around the rhizosheath, which gets replenished from the bulk (surrounding) soil
INTERCEPTION
- nutrient doesn’t move, but rather, the root moves to the nutrient (basically just bumps into it).
Explain the antagonistic interactions in ion uptake by roots.
Sometimes, the uptake of one ion affects the uptake of another ion.
e. g. large uptake of Na = ↓ uptake of Ca, so a reduction in growth might not be because of high sodium concentration but because of low [Ca].
e. g. applying lots of Ca decreases uptake of Mg
e. g. high Cl uptake = ↓ nitrate uptake
What’s the mobility and method of movement (% of uptake) for:
Phosphorus (P)
- Immobile
- Mass flow = 6%
- Diffusion = 91%
- Root interception = 3%
True or false?
Sodium is an essential nutrient.
True, but only for some plants.
List the 6 essential macronutrients
- Nitrogen (N)
- Phosphorus (P)
- Potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Sulphur (S)
Explain what a transient nutrient deficiency is and how it might come about (and be resolved)
Transient deficiencies are those that correct themselves when conditions change.
e.g. a period of prolonged cool, dry conditions could induce transient P, B, Zn, K, Fe, and/or Mn deficiencies due to low rates of diffusion and mass flow, which would be rectified once the soils warms- and wets-up.
K uptake is also related to metabolic activity, so during a period of low/reduced metabolic activity (stress, low light, etc.), a transient K deficiency can develop.
True or false?
Silicon (Si) is an essential nutrient.
True; it’s essential for some plants, and beneficial for others.
What’s the mobility and method of movement (% of uptake) for:
Sulphur (S)
- Mobile
- Mass flow = 95%
- Diffusion = 0%
- Root interception = 5%
Explain what the rhizosheath is and its importance.
- The rhizosheath is the column of soil that adheres to the root as you extract it from the soil.
- The soil sticks because of root hairs and exudates, so its no wonder that the size of the rhizosheath is related to the density and size of the root hairs.
- there’s some evidence to suggest that plants with a greater rhizosheath have the ability to take up more P when it’s limiting (probably due to root hair morphology).
How can compaction affect nutrient movement and uptake in soil?
- Interception:
- if root growth is restricted due to compaction, nutrient uptake will also be restricted
- if root growth isn’t restricted, nutrient uptake will be increased due to greater soil-root contact
- Mass flow:
- Compaction will reduce water movement and therefore nutrient movement (and uptake) via mass flow
- Diffusion:
- If compaction increases the distance between the nutrient and the root surface, nutrient movement and uptake will be reduced.
What’s the mobility and method of movement (% of uptake) for:
Nitrogen (N)
- Mobile
- Mass flow = 98%
- Diffusion = 0%
- Root interception = 2%
Is Selenium (Se) an essential, beneficial, or toxic nutrient?
It’s essential for animals and humans, but not plants.
What’s the mobility and method of movement (% of uptake) for:
Magnesium (Mg)
- Mobile
- Mass flow = 87%
- Diffusion = 0%
- Root interception = 13%
Explain the 4 R concept of nutrient management.
Right rate
- Applying enough to meet plant needs (i.e. critical levels) without applying in excess
- To determine what the right rate is, use soil and plant tissue testing and economic assessments (ferts are expensive!)
Right time
- Nutrient requirements change during the growing season
- Therefore, nutrients should be supplied at varying concentrations throughout the season to match demand
- Could include strategic applications of nutrients throughout the season and/or soil/fert management strategies that allow for varied nutrient release
Right place
- Putting nutrients where uptake will be maximised (i.e. foliar, rhizosphere).
- Need to recognise that soil is heterogenous, so need to match fert application with spatial variability
Right source
- Characteristics of the soil determine the availability of nutrients, and therefore which source would be best.
- can overcome this with new formulations or delivery systems (e.g. liquid vs granular, surface vs in-furrow, etc.)
- Influenced by price and availability
What are the consequences of fertiliser form, soil properties, and the mobility of nutrients on diffusive transport?
- The greater the solubility, the greater the concentration gradient created, and therefore the greater the rate of diffusion (and uptake)
- Soil texture, moisture, and temperature affect diffusion and influences uptake
- ↑ clay content = ↓ tortuosity (impedance) = ↑ diffusion rate
- soil texture also influences the CEC and buffering capacity of the soil, which will effect the rate of diffusion (↑ CEC/buffering capacity = ↓ diffusion)
- ↓ moisture = ↑ tortuosity (pathway distance) = ↓ diffusion rate
- ↓ soil temp = ↓ diffusion rate
- ↑ clay content = ↓ tortuosity (impedance) = ↑ diffusion rate
- immobile nutrients are more likely to move via diffusion, and the amount that they’re affected by these other properties (e.g. moisture and temp) is affected by their mobility
- For example, P relies on diffusion as the means of transport more than K (they’re both immobile), and the rate of P diffusion is affected by temperature more than the rate of K diffusion.
What’s the mobility and method of movement (% of uptake) for:
Calcium (Ca)
- Mobile
- Mass flow = 72%
- Diffusion = 0%
- Root interception = 28%
What’s the mobility and method of movement (% of uptake) for:
Copper (Cu)
- Immobile
- Mass flow = 20%
- Diffusion = 10%
- Root interception = 70%
True or false?
The concentration of nutrients in the vacuole is greater than in the cytosol.
False. The vacuole is used for nutrient storage so the plant can buffer growth against changes in nutrient supply.
What’s the mobility and method of movement (% of uptake) for:
Potassium (K)
- Immobile
- Mass flow = 20%
- Diffusion = 78%
- Root interception = 2%
Why are higher amounts of phosphorus (P) required to maintain production in Australia compared to the rest of the world?
Because many soils in Australia are very low in P or are highly P fixing.
True or false?
Plant roots can modify the environment around them.
True; they can create localised changes in pH to enhance the uptake of nutrients in that area.
There’s considerable genetic variation between species in their ability to change the rhizosphere pH.
Is Aluminium (Al) an essential, beneficial, or toxic element?
Potentially toxic.
