Analyse the processes of soil and water degradation, including erosion, structural decline, salinity, acidification and nutrient pollution, and the management practices that influence them

What this dot point is asking

NESA wants you to identify the main processes that degrade the soil and water resource, explain the cause of each, and connect them to specific management practices that either accelerate or slow the damage. The verb "analyse" means you must break each process into cause, mechanism and effect, then show how a farm decision feeds into it. The strongest answers name a real Australian landscape and a real practice rather than talking in generalities.

The answer

Soil erosion

Erosion is the removal of topsoil by water or wind, and it strips the most fertile, nutrient-rich layer. Water erosion progresses from sheet erosion (a thin uniform layer lost across a slope), to rill erosion (small channels), to gully erosion (deep, unrecoverable channels such as those scarring parts of the NSW central west). Wind erosion lifts fine particles from bare paddocks, as seen in dust storms off the Mallee and western plains. The single biggest driver is loss of groundcover: overgrazing, over-cultivation and bare fallows leave soil exposed to raindrop impact and wind. Maintaining at least 70 percent groundcover, retaining stubble and using contour banks dramatically reduce erosion.

Structural decline

Structure degrades when aggregates collapse and pores close. Compaction from heavy machinery and from stock trampling wet soil (pugging) reduces infiltration and restricts roots. Surface crusting forms when raindrops shatter bare aggregates and the surface seals on drying, which then increases runoff and erosion. Working soil when too wet or too dry, and the loss of organic matter, both accelerate structural decline. Controlled traffic, reduced tillage and maintaining groundcover and organic matter protect structure.

Salinity

Salinity is the accumulation of salts in the root zone or in waterways. Dryland salinity occurs when deep-rooted native vegetation is cleared and replaced with shallow-rooted annual crops and pastures: less water is used, the watertable rises and carries stored salt to the surface, killing plants and scalding land. This is widespread across the Murray-Darling Basin. Irrigation salinity occurs when irrigation adds water faster than it drains, raising watertables and concentrating salt. Reversing it means restoring deep-rooted perennials and trees, improving drainage and using water more efficiently.

Acidification

Australian agricultural soils acidify naturally over decades. Nitrate leaching below the root zone leaves acidity behind, ammonium and legume-based nitrogen add hydrogen ions, and product removal exports alkalinity. Below about pH 5 (calcium chloride), aluminium becomes toxic and roots are stunted. The granite-derived soils of the southern and central tablelands are strongly affected. The correction is regular liming, but because acidity stratifies down the profile, subsurface acidity can persist even under a limed topsoil.

Nutrient pollution of water

Nutrients lost off-farm degrade water resources. Phosphorus bound to eroded soil and dissolved nitrogen wash into rivers and dams, where they fuel eutrophication and toxic blue-green algal blooms, such as the major Darling River blooms. Over-application of fertiliser, poor effluent management at intensive piggeries and dairies, and erosion all contribute. Nutrient budgeting, buffer strips and fencing stock out of waterways reduce the load.

How to use this in the exam

Treat each process as cause, mechanism, effect, then management. For full marks, link a specific practice to the process: "removing deep-rooted vegetation reduced water use, so the watertable rose and brought salt to the surface." Anchor at least one process in a named landscape such as Murray-Darling Basin dryland salinity or central west gully erosion, and finish by judging whether the practice is preventing or merely treating the damage.