General Flashcards
Accessibility of nutrients - Mass flow
Mass flow is the movement of dissolved ions withthe flow of water (water is flowing into the plant as water moves upwards by evaporation, and into the root by transpiration - water is therefore flowing and has ions in it). Sometimes this is enough, sometimes it isn’t
Accessibility of nutrients - diffusion
Movement from high to low concentrations, to equalise concentration gradients. If plant is taking out nutrients faster than mass flow replenishes them, thenthere is a depletion zone around the root (i.e. if uptake> replenishment) - leads to depletion (e.g. P, Zn).
Accessibility of nutrients - interception (by roots)
Root growth towards nutrients. Depends on:
- How much roots expand through the soil
- Efficiency of absorption by root haris
But, for e.g. P, don’t get enough by this method alone
Distance moved by diffusion
The distance a nutrient can move by diffusion will increase with increasing soil water content. With increased water content, nutrients such as K+, NO3- can take straight path. If water content low, pathway longer (tortuosity). NO3- moves furthers because nearl all of it is in solution, whereas other compounds are on exchange sites, or sorbed tightly
Accesibility of nutrients - relative importance varies
- P not much in soil solution, so mass flow low, relies heavily on diffusion
- With Ca, Mg, Su, N lots in solution, so lots of mass flow
Soil physical properties which affect movement of water and nutrients
- Texture - particle size distribution, surface area
- Structure - paths for water and air movement, root growth and nutrient movement. Biological activity 0 if you change amount of water, you also change how quickly microbes move nutrients between pools
- Structural stability - confers resistance to structural breakdown by rainfall and tillage. (surface crusts, impeded water infiltration, runoff, erosion)
- Soil strength - (affects penetration of roots)
how does soil minimise changes in soil solution chemistry?
Buffering using CEC. When cation added, it quickly equilibrates with exchange cations, removing K+ solutions from solution. If plant removes cation, it is replenished from cation exchange site pool
How is soil pH buffered?
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For CEC and pH buffering what soil components contributed most to CEC?
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Plants access nutrients via 3 methods?
interception, mass flow, diffusion
Soil physical properties play important role in chemical fertility through:
- Effect on root growth (soil strength)
- Aeration (number and size of pores)
- Water movement
- Erosion
Soil fertility
What is the concentration called at which yield is maximised?
the lower critical concentration
Soil fertility
Will a deficiency of non essential elements result in a decrease in crop yield/ plant growth?
No, for non essential elements only have second part of graph. Only problem is potential toxicity, plants can grow to maximum without these elements. At the ‘critical concentration’ the concentration of a non essential element (or essential element) becomes too high, and the yield decreases due to toxicity
Micronutrients (trace elements)
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The availability of most trace metals is low at a pH of 8 because their hydroxide salts are very insoluble?
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