W6, Uptake of nutrients by leaves + diagnosing nutritional disorders Flashcards
What’s the problem, what causes it, and how would you prevent or fix it?
Bitter pit in apple.
Caused by calcium deficiency
Contributing factors: poor watering and dry conditions + exacerbated by high N
Prevented by foliar applications of calcium during flowering.
(calcium is relatively immobile in plants and is transported in xylem, but fruit don’t transpire, so calcium isn’t transported to them easily)
What causes split seed in lupins, and how can it be prevented or corrected?
- Results from a manganese (Mn) deficiency which impairs the development of the seed coat
- Develops during flowering, pod set, and grain fill (high growth = high Mn demand)
- More common after dry weather
- Can be prevented by foliar applications of Mn just leading up to flowering and early pod set
- Mn is immobile in plants
What causes pollen blast in apples and pears, and how can it be prevented or corrected?
- The result of boron deficiency
- Flowers and pollen have a high boron requirement
- B is immobile in plants
- Apply as a foliar spray in Autumn.
What would the effect be on a wheat crop that had its foliage sprayed with 13 kg N/ha as urea at flowering?
A significant increase in grain protein (~2.5%).
By around 25 days after flowering though, there’s no longer any positive effect to be gotten from foliar fertilising.
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Why is the uptake of cations through leaves quicker than anions?
Because the cuticle is highly negatively charged, and that negative charge increases further into the leaf, which attracts cations and allows them to move easily through.
True or false?
Nutrients applied to the leaves enter through the stomatal openings.
False.
Nutrients don’t move in or out of the stomata, but rather through pores that surround them (and trichomes).
The greater the number of stomata and trichomes, the greater the density of pores, and the greater the rate of nutrient uptake through the leaves.
What is the primary driver of nutrient uptake through the leaves?
A concentration gradient.
The greater the gradient, the faster the uptake.
How can you improve the effectiveness of foliar sprays?
- Maximise the amount of contact with the leaf surface and the length of time contact is maintained
- spray when humidity is high (vapour pressure deficit is low), temperature is low, and wind speed is low.
- early morning/evening
- cool cloudy days
- shortly after rain
- = ↓ evaporation
- = ↑ uptake (high leaf turgor improves uptake)
- use adjuvents
- = ↑ droplet retention
- = ↑ solubility (and uptake)
- = ↓ surface tension = ↑ spread over leaf
- use appropriate sprayer nozzle to achieve good coverage
- want to cover as much of the leaf area as possible, including the undersides of leaves - most plants have more stomata (and therefore pores) on the undersides of their leaves.
- spray when humidity is high (vapour pressure deficit is low), temperature is low, and wind speed is low.
- Add sucrose (urea)
- can reduce the amount of leaf burn and increase uptake for foliar urea considerably
- Add urea (micronutrients)
- adding a small amount of urea can increase the uptake of micronutrients
- Ensure pH between 4.5-6.5
- too acid or alkaline = leaf damage
- charge of cuticle is affected by pH, and if you screw with the pH too much you can affect the relative amounts of positive and negative charge, thus affecting nutrient transport.
- Ensure chemical compatibility
- e.g. cheap options for applying calcium and zinc = Ca(NO3)2 and ZnSO4, but if you applied those together you’d end up with CaSO4 (gypsum) precipitating.
What are the risks associated with using foliar sprays that have a high salt index (e.g. potassium chloride, ammonium nitrate, or urea), and how can the risk(s) be managed?
The main risk is leaf burn caused by osmotic shock (i.e. rapid localised dehydration). The risk of this can be overcome with higher dilution.
True or false?
Chelated Zn, for example, will have a greater positive effect on the maximum potential yield that can be achieved, and will achieve it faster than using zinc sulfate (ZnSO4)
False.
Chelated Zn will achieve the maximum potential yield quicker, but it won’t increase the max potential.
What is the most likely cause of these symptoms?
Nitrogen (N) deficiency (entire leaf chlorosis)
What is the most likely cause of these symptoms?
Iron (Fe) deficiency (interveinal chlorosis)
What is the most likely cause of these symptoms?
Potassium (P) deficiency (tip chlorosis and necrosis)
What is the most likely cause of these symptoms?
Zinc (Zn) deficiency (parallel necrotic strips)
What is the most likely cause of these symptoms?
Nitrogen (N) deficiency (stunted, chlorotic, large production of anthocyanin (red pigment)).
What is the most likely cause of these symptoms?
Potassium (P) deficiency (necrotic leaf tips).
Which nutrient deficiencies appear in the oldest leaves first?
Mobile nutrients (N, P, K, Mg)
Which nutrient deficiencies appear in the newest leaves first?
Immobile nutrients (Ca, S, B, Fe, Zn, Mn, Mo, Cu)
What is the most likely cause of these symptoms?
Iron (Fe) deficiency (interveinal chlorosis of younger leaves).
What is the most likely cause of these symptoms?
Phosphorus (P) deficiency (thick rind).
