SUSTAINABLE AGRICULTURE
Australia's fragile environment combined with past management practices
means that the natural resources (soil, water and vegetation) of many
areas are degraded. Natural resource degradation affects our environment
and the quality and quantity of natural resources available to current
and future generations.
People form landcare groups to work together to improve the management
of natural resources and to care for their local environment.
Landcare groups throughout NSW are working on a wide range of sustainable
agriculture issues. These include:
· Salinity (irrigation, dryland,
urban)
· Soil degradation (acid soils, soil erosion,
acid sulphate soils)
Salinity
Salinity results from groundwater rising to the surface of the land
and bringing with it salts that naturally occur in these water systems.
Native trees and plants with their deep roots were once effective at
using most of the water entering the soil from rainfall, thereby preventing
groundwater from rising.
Large amounts of native trees and plants have been cleared and replaced
with annual crops and pastures, irrigated agriculture and town gardens
and lawns that have shallower roots and different growth patterns. This
has allowed more rainfall to leak into groundwater, causing the watertable
to rise and bring salts to the surface.
Salts accumulating near the surface cause widespread land, water and
environmental degradation. Salinity can kill or stunt trees, crops and
pastures in rural areas, and damage buildings and other structures in
urban areas.
As water is diverted for irrigation, urban and industrial water supplies,
there is less flow to dilute the salt washing into rivers and streams.
Increased salinity levels in rivers limits the usefulness of water supplies
to towns, irrigation developments and aquatic ecosystems.
Irrigation salinity and waterlogging
The issue
In many irrigation areas, salinity problems have been increased by
the large amount of water which is applied to crops and pastures.
Waterlogging is a separate but related problem that occurs when soil
is saturated with water for longer than one day. Waterlogging contributes
to rising watertables. Shallow watertable areas are more prone to waterlogging.
Salinity and associated waterlogging problems are increasing in NSW
irrigation areas, particularly in the Murray and Riverina.
What can be done?
Improved soil, crop and water management combined with revegetation
on strategic sites can help prevent salinity problems and reclaim affected
land.
The amount and duration of water lying on the ground needs to be minimised
to prevent the development and spread of shallow watertables. This can
be done through better surface and sub-surface drainage, improved irrigation
systems, groundwater pumping, reuse of water and changes to the timing
of irrigation.
The planting of trees and use of salt-tolerant plants helps to manage
existing shallow watertable areas. Resting land from intensive irrigated
production can help to slow and prevent salinity problems.
Dryland salinity
The issue
Dryland salinity occurs when groundwater, and the salts it contains,
rise to the soil surface. It is mainly due to the clearing of deep-rooted
native vegetation for rain-fed crop and pasture production.
Dryland salinity causes vegetation loss and the formation of bare areas
that are susceptible to erosion. It occurs predominantly on the tablelands
and western slopes of NSW and is associated with less productive land.
What can be done?
The development of dryland salinity can be slowed by retaining native
vegetation, revegetating recharge areas in the upper parts of catchments,
and replacing annual shallow-rooted crops and pastures with perennial
deep-rooted pastures.
There are several ways to help repair land affected by dryland salinity,
including:
· fencing off affected areas and reducing stocking rates
· using salt-tolerant grasses, herbs, shrubs and trees to revegetate
affected areas
· surface mulching, surface tillage or deep ripping to assist
plant germination
· subsurface drainage
· changing land and water management to reduce the amount of
water seeping into the watertable.
Urban salinity
The issue
Urban salinity is caused by rising watertables. The replacement of
deep-rooted native trees and plants with lawns and gardens has allowed
more rainfall to leak into groundwater, causing the watertable to rise
and bring salts to the surface.
Salinity in urban areas results in bare patches of soil, unhealthy
or dead plants, corrosion of structures and waterlogged ground. It affects
the quality of drinking water, causes roads, bridges, buildings and
house foundations to crumble, corrodes plumbing and can have a serious
impact on native plants and animals.
Urban salinity occurs to some degree in most towns on the western slopes
of the Great Dividing Range.
What can be done?
Prevention and treatment of urban salinity includes:
· growing mainly native plants which require less water
· minimising vegetation clearing
· revegetating key areas
· identifying areas susceptible to rising watertables.
For further information on all forms of salinity please click here.
(Information courtesy of the NSW Government)
Soil Degradation
Acid soils
The issue
Some soils are naturally acid, and others become acid from many years
of intensive agriculture, especially the growing of annual shallow rooting
legume pastures, production of hay and use of ammonium fertilisers.
Soil acidity affects a pasture's ability to establish good ground cover
and deep roots. This lack of cover and plant vigour causes the land
to be susceptible to weed infestation and erosion.
Soil acidity also makes it difficult to manage other degradation problems
¾ it is hard to grow perennial pastures to slow dryland salinity
and obtaining sufficient groundcover to slow erosion is difficult on
acid soils.
What can be done?
There are several measures which can be taken to prevent or repair
acid soils, including:
· using less acidifying farming systems
· applying lime to reduce and prevent soil acidity
· using deep-rooted perennial pastures.
Soil erosion
The issue
Sheet erosion is the removal of
soil on sloping land by rainfall and flowing water.
Rill erosion is the removal of soil
by rainfall and flowing water, forming channels up to 30cm deep.
Gully erosion is the removal of
soil by water flow forming channels deeper than 30cm, down which sediment
and suspended materials flow.
Wind erosion occurs when soil particles
are detached from the soil surface and are blown away by wind.
Sheet, rill and gully erosion cause soil, nutrients and plants to be
removed and washed into rivers or onto other land. Eroded land becomes
less productive because the soil and nutrients are lost. Chemicals can
spread from the eroded material and pollute waterways or affect marine
life.
Wind erosion removes fine soil particles leaving only larger particles.
This reduces the amount of nutrients left in the soil and the soil's
ability to hold moisture for plant growth. Wind erosion can also lead
to dust storms, causing air pollution.
Erosion occurs when the soil is bare and not covered by plants. This
often results from surface soil problems such as salinity, sodicity
and structural degradation. It frequently occurs as a result of excessive
cultivation, overclearing, overgrazing and drought. Wind erosion occurs
in areas that are exposed to wind, especially on sandy soils.
What can be done?
Methods for preventing and treating erosion include:
· ensuring soils are covered with vegetation
· contour farming and strip cropping
· conservation farming, including reduced tillage, stubble retention
and improved crop rotations
· reduced stocking rates and pasture improvement
· soil and water conservation earthworks.
Wind barriers and groundcovers on bare areas help to slow down wind
velocity and therefore reduce wind erosion.
Acid Sulphate Soils
The issue
Development in estuarine floodplains of coastal NSW for agriculture,
urban development and sand mining has exposed soils which are naturally
waterlogged and rich in iron sulphides. When these soils are exposed
to air, sulphuric acid is produced, hence the name acid sulphate soils.
This sulphuric acid moves through the soil, acidifying soil water,
groundwater and eventually surface waters, having a severe impact on
the environment.
Soil can become so acid and toxic that few plants will grow from it
and the surface can become bare and scalded. This affects agricultural
productivity and the natural environment. The acid also corrodes concrete,
iron and steel, damaging pipelines, bridges, floodgates and other structures.
Heavy rain in areas of acid sulphate soils can cause the acid water
to flow into estuarine environments, resulting in fish kills and degrading
of estuarine habitats. Acid sulphate soils also affect fish by lowering
growth rates and damaging their skin and gills.
What can be done?
Measures to prevent acid sulphate soils from occurring and to repair
affected areas include:
· research into the distribution of soils which contain iron
sulphides.
· avoiding disturbance or drainage of soils containing iron sulphides.
· applying lime to neutralise the sulphuric acid (costly for
large areas)
· covering land with water to prevent the soils from being exposed
to air
· use of wide, shallow drains to drain quickly from the surface
of low-lying land without exposing the iron sulphide layer beneath the
soil.
For further information on acid sulphate soils please click here.
(Information courtesy of the NSW Government)
For further information on all forms of soil degradation please
click here.
(Information courtesy of the NSW Government)
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