Quick questions on Soil and water degradation explained: HSC Agriculture Plant Production

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.

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.

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.