Week 12 - Nutrient Cycling

Question 1

What are the processes which remove nutrients from the soil solution and eventually return them?

Answer 1

• immobilisation followed by mineralisation
• removal from solution to exchange sites and return
• chelation by organic matter and release
• chemical adsorption by soil solids and release, for example phosphate.

Answer 2

What do inputs to the nutrient cycle include?

• nutrients dissolved in the rain (i.e. NH4+ or SO42-);
• nutrients applied as fertiliser (either inorganic or organic);
• nutrients fixed from the atmosphere by microbes or microbial symbionts (i.e. leguminous plants trap atmospheric N2 as NH4+);
• nutrients derived from the breakdown of parent materials.

Question 3

What do losses from the nutrient cycle include?

Answer 3

Losses from the system include;

• nutrient losses to the atmosphere via volatilisation of volatile elements (for example NH4+ is lost as NH3 gas under alkaline conditions);
• nutrient leaching with drainage water (for example NO3-, SO42-, Cl-);
• nutrient loss due to the export of farm produce off farm as animal or plant products.