Macronutrient cycling

Question 1

Nitrogen cycle stages

Answer 1

mineralisation
nitrification
denitrification
volatilisation

Question 2

chemical process of mineralisation

Answer 2

organic N —> ammonium

Question 3

Chemical process of nitrification

Answer 3

Ammonium—> NO2- —> NO3-

Question 4

Chemical process of Denitrification

Answer 4

NO3- —> N2/N2O under anaerobic conditions

Question 5

Chemical Process of volatilisation

Answer 5

Ammonium —> NH3 gas loss in high pH soils

Question 6

how mobile is N

Answer 6

N is highly mobile especially as NO3-

Question 7

Features of Phosphorus in sool

Answer 7

mainly exists as H2PO4- and HPO4,2-
strongly bings to Fe and Al oxides or precipitates as calcium phosphate in high pH soils
immobile in soil, highly dependent on pH to be available
Olsen P test is used to measure P availability

Question 8

Features of sulphur in soil

Answer 8

Inorganic form: SO4 2- which is mobile
Organic sulphur: C-S bonds in amino acids
Redox Reactions: FeS2 (pyrite) forms in anaerobic conditions- oxidation of pyrite leads to acidity
Mineralisation and immobilisation are microbial and dependent on C:S ration

Question 9

Features of Potassium

Answer 9

Exists in multiple forms:
Solution K+, immediately available
exchangeable K+, readily available
Fixed K+, slowly released from clay layers

Illite and Vermiculite clays have high K fixing capabilities
losses can occur via leaching or export in hay/milk