Lecture % Reactions at surfaces

Question 1

Montmorillonite

Answer 1

layers with negative charges connected by positive charges
solid clay surface and cations
more nutrients at surface

Question 2

humus

Answer 2

negatively charged and attracts cations

Question 3

cation exchange

Answer 3

weak bonds between cations and charged surfaces
dynamic equilibrium
cations determine soil acidity

Question 4

soil texture

Answer 4

high cation exchange capacity so more nutrients and more acidic

Question 5

cation exchange with OA

Answer 5

root exudates release CO2 and OA
H+ makes soil acidic

Question 6

soil acidification

Answer 6

mineral composition of parent material and weathering

Question 7

processes that cause acid soil

Answer 7

rainfall and acid rain
plant growth
root respiration and OM decomposition
fertiliser
oxidative weathering

Question 8

processes that cause alkaline soils

Answer 8

weathering of silicates
adding limestone
high bicarbonate water

Question 9

problems with pH

Answer 9

changes nutrient availability
higher pH=more negative charge sites=high CEC

Question 10

anion exchange

Answer 10

bind to positively charged clay surface impurities of minerals

Question 11

soil nutrient mobility

Answer 11

entry (anthropogenic, degradation, weathering)
leave (leaching, uptake)
dynamic equilibrium

Question 12

negative charge

Answer 12

clay and humus

Question 13

positive charge

Answer 13

iron and aluminium oxides

Question 14

what is soil dominated by

Answer 14

negative surfaces

Question 15

phosphate and nitrate

Answer 15

mobile as cannot stick so plants uptake but also leach

Question 16

ammonium

Answer 16

attracted to low mobility clays
enters dynamic equilibrium
not always bioavailable

Question 17

depletion zone

Answer 17

surrounding roots
mass flow