Soil 364 - Exam 2

potassium (K)

highly soluble macronutrient that doesn’t precipitate, mobile, used in gradients, catalysts, hydraulic gradients

K accessibility in soil

only 1% is found in soil solution, of that 2% is available to plants

adsorbed forms of K

exchangeable (K+ on CEC sites of clay and OM), non-exchangeable (fixed inside clay minerals and resistant to weathering)

% base saturation

the extent to which the absorption complex of a soil is saturated with base forming cations (not Al or H)

egg carton effect

clay has spaces between layers that match the size of K, traps K and only NH4+ can displace cations

luxury consumption

Plants take up K as much as they can even if its not needed, which displaces other cations (Mg, Ca). Leads to deficiencies in other cations with lower affinities

K deficiency symptoms

In older leaves, chlorosis and necrosis on leaf edge, white necrotic spots, plants fall over

problems with K in the environment

Excess K on exchange sites lead to luxury consumption. Milk fever from Ca displacement causes low clotting and livestock can bleed to death, Grass tetany due to Mg displacement causes death, convulsions, and pedaling motion

What environmental variables effect K?

Low O2 levels decrease K uptake, low soil moisture increases K fixation (needs to move in soil solution), high rainfall/irrigation leaches K

When is the best time to apply K?

Apply around rooting/germination, annually in the spring

Extraction Theory

Extract K from clay by exchanging it with NH4+, 90% is extracted which is a source of error, analyze using flame photometry

saline soils