SOILSCI221 EXAM MIDTERM QUESTIONS AND
ANSWERS LATEST UPDATE
In what forms can K be found in?
exchangeable form (adsorbed onto the colloid)
fixed between the clay layers
In weathered primary minerals
Is there a gaseous form of K?
Nope (just like P)
Does K have to change form in the decomposition process?
Nope
What roles does K play in the plant?
required for opening and closing of stomata by guard cells, increases size and quality of
fruits, grains and veggies--essential to quality of forage crops, accelerates growth of
meristem tissue, encourages root growth and increases crop resistance to disease, and
winter hardiness
Is K incorporated into the plant molecules themselves?
Nope, stays in the cytoplasmic solution
Does K have to be mineralized outside of plant when it dies?
Nope, just leaches out
Is K mobile?
Yep!
Where do you see K deficiencies appear?
yellowing along edges or margins of the leaves
What is luxury consumption in terms of K?
when K is taken up more than that needed for optimum growth. (can make animals sick
if they consume plants with too much K). So if there's too much K in the soil, plants can
take up way too much and be wasteful (especially with grain)
What are the pools of K in the soil?
primary minerals-- need to be weathered (feldspars, micas), secondary minerals
(vermiculites illites--from mica), K adsorbed in the colloid/water = readily available
What is the most readily available form of K?
absorbed in the soil solution: concentrations range from 1-10 ppm. But anything in the
soil solution is subject to loss (and when K is adsorbed to a soil colloid)
Is there organic K?
Nope
What does the size of readily available K depend on?
primarily CEC (soil texture, mineralogy), concentrations: 20 to 1000 ppm
How do plants release K+ from the cation exchange complex?
K has a large hydrated radius but is weakly held so the root exudates carbonic acid
(containing H+ )and shares it with the clay particle forcing the K+ to move away from the
colloid and onto the root
So in other words, H+ is produced by root, replaces K+ on colloid, pushing it into the soil
solution and onto the root where it is absorbed.
ANSWERS LATEST UPDATE
In what forms can K be found in?
exchangeable form (adsorbed onto the colloid)
fixed between the clay layers
In weathered primary minerals
Is there a gaseous form of K?
Nope (just like P)
Does K have to change form in the decomposition process?
Nope
What roles does K play in the plant?
required for opening and closing of stomata by guard cells, increases size and quality of
fruits, grains and veggies--essential to quality of forage crops, accelerates growth of
meristem tissue, encourages root growth and increases crop resistance to disease, and
winter hardiness
Is K incorporated into the plant molecules themselves?
Nope, stays in the cytoplasmic solution
Does K have to be mineralized outside of plant when it dies?
Nope, just leaches out
Is K mobile?
Yep!
Where do you see K deficiencies appear?
yellowing along edges or margins of the leaves
What is luxury consumption in terms of K?
when K is taken up more than that needed for optimum growth. (can make animals sick
if they consume plants with too much K). So if there's too much K in the soil, plants can
take up way too much and be wasteful (especially with grain)
What are the pools of K in the soil?
primary minerals-- need to be weathered (feldspars, micas), secondary minerals
(vermiculites illites--from mica), K adsorbed in the colloid/water = readily available
What is the most readily available form of K?
absorbed in the soil solution: concentrations range from 1-10 ppm. But anything in the
soil solution is subject to loss (and when K is adsorbed to a soil colloid)
Is there organic K?
Nope
What does the size of readily available K depend on?
primarily CEC (soil texture, mineralogy), concentrations: 20 to 1000 ppm
How do plants release K+ from the cation exchange complex?
K has a large hydrated radius but is weakly held so the root exudates carbonic acid
(containing H+ )and shares it with the clay particle forcing the K+ to move away from the
colloid and onto the root
So in other words, H+ is produced by root, replaces K+ on colloid, pushing it into the soil
solution and onto the root where it is absorbed.
