W8.1, Potassium (K) nutrition Flashcards
True or false?
We apply enough K in australian agriculture.
False. For much of the cropland in Australia, we’re in a negative K balance (removal exeeds input); i.e. we’re mining soil K.
Our soils currently have large quantities of K, so there hasn’t been much economic loss from not adding K (yet).
Where would you expect K to be concentrated on a farm?
Around stock water and rest areas.
Where crop stubble/biomass has been concentrated (e.g. in the same rows).
True or false?
Potassium uptake can contribute to rhizosphere acidification.
True. Potassium is taken up as K+, and to maintain charge balance, H+ can be exuded.
What is the role of potassium in plants?
- Osmoregulation
- Maintaining turgor
- Supporting expansive growth (e.g. stem elongation, fruit growth)
- helps with tolerance to drought, frost, etc.
- Major cation for maintaining charge balance
- Activates enzymes (i.e. they can only function properly in the presence of K)
- e.g. starch synthase
- = ↑ starch production in crops like potato, sweet potato, tomatoes, grapevines, and sugarcane.
- e.g. starch synthase
- Regulates photosynthate translocation
- higher [K] = higher rate of sap flow in phloem from leaves to fruits
- Defence against oxidative stress (free radicals)
- Tolerance to stress
- biotic and abiotic (net blotch, powdery mildew, frost, drought)
True or false?
More potassium = better stress tolerance.
True, but only to a point. Adding more K beyond that which would correct a deficiency is unlikely to have any beneficial effect.
True or false?
Potassium uptake is related to plant metabolism.
True.
Potassium uptake is via specialised K+ channels and relies on a proton pump to maintain charge balance, which is regulated by metabolic activity (so plants that are under stress, photosynthesising slowly, growing slowly, etc. will take up less K than those growing prolifically).
Where is most of the K located in a cereal crop, and what are the consequences of this (especially in terms of management)?
In the straw.
Means that if you crop in the same row year after year you will get banding of K as the straw breaks down.
Also means that if you export the straw you’re removing a lot of K.
True or false?
Potassium availability limits the effectiveness of other nutrients.
True (think Liebig’s law of the minimum).
True or false?
Potassium deficiency is more common in finely textured soils (clays).
False; it’s more common in coarsely-textured soils (it’s adsorbed more readily in clays).
True or false?
Potassium and calcium interact negatively (high Ca2+ reduces uptake of K+)
False. Potassium and sodium interact strongly, and a high [Na+] will result in reduced K+ uptake. Calcium mediates the antagonism.
What kinds of crops need to be supplied with lots of K?
Horticultural crops.
True or false?
Potassium deficiency is more common in high rainfall areas.
True.
What other cationic nutrients are antagonistic with potassium?
Sodium.
- Increasing the ability of a plant to exclude sodium will increase it’s uptake of potassium (and vice versa; i.e. the lower the [leaf K], the higher the [leaf Na]).
Magnesium
- Potassium reduces the uptake of magnesium.
- The cause of grass tetany (hypomagnaesia (magnesium deficiency)) in ruminants.
What are the two potential negative effects of increasing K concentration in citrus?
Increased rind thickness and less colour.
Everything else (size, weight, rind creasing, pugging, and splitting, post-harvest storage, and juice quality) are all improved.
How does potassium influence grain filling?
Starch synthesis in grain depends on potassium (starch synthase), so inadequate K means inadequate grain filling = small grains = higher screenings.
