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Soils in NSW

What does soil do for us?

Soils are living systems that are vital for producing our food and fibre as well as for maintaining the ecosystems on which almost all life ultimately depends. Soil directly and indirectly affects agricultural productivity, water quality and the global climate through its function as a medium for plant growth, a regulator and partitioner of water flow, and an environmental buffer.

A greater variety and quantity of living creatures, especially microorganisms, usually exist in fertile soil compared to any other environment above ground.

Soil provides a physical matrix, chemical environment and biological setting for water, nutrient, air and heat exchange for living organisms.

Soil controls the distribution of rainfall or irrigation water to runoff, infiltration, storage or deep drainage. Its regulation of water flow affects the movement of soluble materials such as nutrients or pesticides.

Soil regulates biological activity and molecular exchanges among solid, liquid and gaseous phases. This affects nutrient cycling, plant growth and decomposition of organic materials.

Soil acts as a filter to protect the quality of water, air and other resources.

Soil provides mechanical support for living organisms and their structures. People and wildlife depend on this function.

Three special functions of soil

Soils make it possible for plants to grow. Soils mediate the biological, chemical and physical processes that supply nutrients, water and other elements to growing plants. The micro–organisms in soil transform nutrients into forms that can be used by growing plants. Soils are the water and nutrient storehouses on which plants draw when they need nutrients to produce roots, stems, and leaves. Eventually, these become food and fibre for human consumption. Soils–and the biological, chemical and physical processes that they make possible–are a fundamental resource on which the productivity of agricultural and natural ecosystems depend.

Soils regulate and partition water flow through the environment. Rainfall in terrestrial ecosystems falls on the soil surface where it either infiltrates the soil or moves across the soil surface into streams or lakes. The condition of the soil surface determines whether rainfall infiltrates or runs off. If it infiltrates the soil, it may be stored and later taken up by plants, move into groundwater, or move laterally through the earth, appearing later in springs or seeps. If it runs off, it may remove the soil itself and attached nutrients causing loss of soil depth and off–site pollution. This “partitioning” of rainfall between infiltration and runoff determines whether a storm results in soil water replenishment or a damaging flood. The movement of water through soils to streams, lakes and groundwater is an essential component of recharge and base flow in the hydrological cycle.

Soils buffer environmental change. The biological, chemical and physical processes that occur in soils buffer environmental changes in air quality, water quality and global climate. The soil matrix is the major incubation chamber for the decomposition of organic wastes including pesticides, sewage, solid wastes and a variety of other wastes. The accumulation of pesticide residues, heavy metals, pathogens or other potentially toxic materials in the soil may affect the safety and quality of food produced on those soils. Depending on how they are managed, soils can be important sources or sinks for carbon dioxide and other gases that contribute to the greenhouse effect (greenhouse gases). Soils store, degrade or immobilise nitrates, phosphorus, pesticides and other substances that can become pollutants in air or water.

Adapted from: National Research Council 1993, Soil and Water Quality: An agenda for agriculture, National Academy Press, Washington DC.