Sustainable Agriculture – Background Information

Biosecurity is important to the productivity, sustainability and resilience of agriculture in the Northern Agricultural Region. Weeds, pests and diseases can reduce crop and livestock production, increase management costs, affect market access and cause environmental damage.

Preventing the introduction and spread of harmful organisms is generally more effective than managing them once they have become established. Biosecurity is therefore a shared responsibility involving governments, agricultural industries, landholders and the wider community. On farms, good biosecurity practices can include monitoring crops, livestock and pastures for unusual pests or disease symptoms; managing weeds; maintaining appropriate hygiene for vehicles, machinery, livestock and plant material; and reporting suspected exotic or declared pests and diseases.

Climate and land-use change can also influence the distribution and impacts of pests, weeds and diseases, making surveillance, preparedness and adaptive management increasingly important.

More information about invasive plants, animals and diseases occurring in the NAR, and their management, is available on the Biosecurity & Invasive Species background page.

Climate change presents an increasing challenge for agriculture in the Northern Agricultural Region. Rising temperatures, changes in rainfall, more variable seasonal conditions and extreme weather can affect crop and pasture growth, water availability, livestock, soils and the timing and reliability of agricultural operations.

Changes in rainfall and temperature can also interact with existing land-management pressures. Reduced or unreliable rainfall can make it more difficult to maintain protective groundcover, increasing the risk of wind and water erosion, particularly on sandy soils. Changes in soil moisture and water balance can also influence salinity, waterlogging and the effectiveness of crop and pasture production.

Building climate resilience involves adapting farming systems to changing conditions through appropriate crop and pasture selection, soil and water management, maintenance of groundcover, improved water-use efficiency, farm planning and the adoption of new knowledge and technologies.

More information on observed and projected climate change in the NAR, its impacts on agriculture and other natural resources, and adaptation and mitigation options is available on the Climate Change background page.

Dryland salinity is a major form of land degradation affecting agricultural landscapes in south-west Western Australia, including parts of the Northern Agricultural Region. Salts occur naturally in many Western Australian soils and groundwater systems, but changes to vegetation and water balance following agricultural development have increased salinity in susceptible landscapes.

The replacement of deep-rooted perennial native vegetation with predominantly annual crops and pastures can increase the amount of water draining below the root zone. Over time, this can cause groundwater levels to rise, bringing dissolved salts closer to the soil surface and into the root zone. Where salt concentrations become sufficiently high, plant growth and agricultural production decline.

Dryland salinity can result in the loss of productive agricultural land and can also affect native vegetation, wetlands and waterways, water quality and infrastructure. Salinity and waterlogging frequently occur together where shallow groundwater and poor drainage affect low-lying areas.

The extent and severity of salinity vary considerably across the landscape. Although dryland salinity has been recognised as a significant problem in Western Australia’s agricultural regions for decades, current information on its total extent and rate of change is limited. Historical estimates and projections should therefore be interpreted with caution.

Managing salinity requires approaches suited to the individual landscape and farming system and is most effective when considered at whole-farm or catchment scale. Management may include reducing groundwater recharge, maintaining or establishing perennial vegetation where appropriate, managing surface water, protecting remnant vegetation and waterways, and using salt-tolerant plants and pastures on affected land. In severely saline areas, management may focus on stabilising and rehabilitating saltland and preventing further degradation rather than returning the land to conventional cropping.

Soil acidity is a major constraint to agricultural production across south-west Western Australia, including the Northern Agricultural Region. Many Western Australian soils are naturally acidic, but agricultural production can accelerate soil acidification through processes including the removal of agricultural products, nitrate leaching and the use of some nitrogen fertilisers.

As soil pH declines, nutrient availability can be affected and aluminium can become increasingly soluble. At sufficiently low pH, aluminium can become toxic to plant roots, restricting root growth and reducing plants’ ability to access water and nutrients. Acidity below the topsoil can be particularly difficult to identify and manage and may substantially restrict crop and pasture growth.

Soil pH should therefore be monitored through the soil profile rather than only at the surface. For Western Australian agricultural soils, recommended minimum targets are pHCa 5.5 in the surface soil (0–10 cm) and pHCa 4.8 in the subsurface soil. Maintaining soil pH at or above these levels helps prevent soil acidity and aluminium toxicity from constraining agricultural production.

Agricultural lime is the principal treatment used to manage soil acidity. Appropriate lime application can maintain or increase soil pH, although correcting established subsurface acidity can take considerable time because lime applied at the surface moves slowly through many soils. Soil testing at different depths, appropriate lime application and ongoing monitoring are therefore important components of long-term soil acidity management.

Soil compaction occurs when soil particles are compressed, increasing soil strength and reducing the pore space available for air, water and root growth. Both surface and subsurface soils can become compacted, although susceptibility varies between soil types.

In agricultural systems, repeated traffic from farm machinery is a major cause of subsurface compaction, while machinery and livestock can also compact surface soils. Sandy agricultural soils, which occur extensively across parts of the Northern Agricultural Region, can be particularly susceptible to compaction.

Compacted soil can restrict crop and pasture root growth, reducing plants’ ability to access water and nutrients and potentially reducing productivity. Restricted rooting depth can be particularly important in dry conditions, when access to moisture stored deeper in the soil profile can help sustain crop growth.

Management depends on the soil type and the depth and severity of the compacted layer. Deep ripping and other forms of strategic tillage can alleviate subsurface compaction in suitable soils, but these treatments are not appropriate for every soil type or constraint. Soil assessment is therefore important before undertaking amelioration.

Preventing re-compaction is also important. Controlled traffic farming, which confines machinery to permanent traffic lanes, can reduce the area of a paddock exposed to repeated wheel traffic and help maintain the benefits of soil amelioration. Managing compaction alongside other soil constraints, such as acidity and water repellence, can also improve the effectiveness and longevity of treatment.

Soil erosion occurs when soil particles are detached and transported by wind or water. Both wind and water erosion affect agricultural land in the Northern Agricultural Region, although wind erosion is a particularly important risk across the region’s extensive sandy soils.

Wind erosion occurs when strong winds move exposed or poorly protected soil. Sandy soils are particularly susceptible, especially when vegetation, crop residues or pasture cover are insufficient. Loss of groundcover following dry seasonal conditions, grazing, cultivation, fire or poor crop and pasture establishment can increase the risk. Wind erosion can remove valuable topsoil and nutrients, damage emerging crops and pastures, reduce long-term soil productivity and transport soil, nutrients, seeds and other material beyond the affected paddock.

Water erosion occurs when rainfall and surface runoff detach and transport soil. The risk increases during intense rainfall where groundcover is insufficient, soils have been disturbed, slopes encourage runoff or water becomes concentrated in drainage lines or other landscape features. Water erosion can remove topsoil, form rills and gullies, damage crops and infrastructure and transport sediment, nutrients and other material into dams, wetlands and waterways.

Maintaining adequate groundcover is one of the most important ways of reducing erosion risk. Retaining crop residues, minimising unnecessary soil disturbance and managing grazing to protect groundcover can help reduce wind and water erosion. On land susceptible to water erosion, appropriately designed surface-water management structures and vegetated waterways may also be required to safely manage runoff.

Erosion risk varies with soil type, landscape position, seasonal conditions and land management. Maintaining year-round groundcover and adapting management to changing seasonal conditions are particularly important for protecting the sandy agricultural soils of the NAR.

Many agricultural soils in the Northern Agricultural Region are naturally low in one or more nutrients required for crop and pasture production. Nutrient availability varies considerably between soil types and can also be affected by rainfall, soil pH, organic matter, previous land use and farming practices.

Agricultural production removes nutrients from the soil when grain, livestock and other products are taken from the farm. Nutrients may also be lost through leaching, runoff, erosion or other processes. Fertilisers, legumes and the recycling of organic materials can help replace nutrients and maintain soil fertility, but nutrient inputs need to be matched to crop and pasture requirements.

Insufficient nutrients can limit plant growth and agricultural productivity, while applying nutrients in excess of plant requirements can increase production costs and the risk of nutrient loss to the environment. Nutrients transported from agricultural land can contribute to declining water quality and ecological impacts in susceptible waterways, wetlands and groundwater systems.

Effective nutrient management therefore aims to provide crops and pastures with the nutrients they require while minimising unnecessary inputs and losses. Regular soil and, where appropriate, plant testing can help identify nutrient constraints and guide fertiliser decisions. Nutrient requirements should be considered alongside soil type, seasonal conditions, crop or pasture requirements and expected production.

Maintaining soil fertility is a long-term process. Monitoring nutrient status and adjusting management as farming systems and environmental conditions change can improve nutrient-use efficiency, maintain agricultural productivity and reduce impacts on surrounding natural resources.

Soil water repellence, also known as non-wetting soil, is an important constraint to agricultural production in parts of the Northern Agricultural Region, particularly on sandy soils. Water repellence occurs when hydrophobic compounds derived largely from organic material coat soil particles and reduce their ability to absorb water.

Instead of wetting evenly after rainfall, water-repellent soils can remain dry in patches or allow water to enter through preferential pathways. This can result in uneven germination and crop or pasture establishment, reduced access to soil water and nutrients, and lower productivity. Poor establishment can also leave soil inadequately protected by vegetation, increasing susceptibility to wind erosion.

Water repellence is particularly associated with sandy soils that have a low clay content. It is an important constraint in the sandy agricultural soils between Gingin and Geraldton, and its expression can be influenced by farming practices and seasonal conditions.

Management depends on the severity of the problem, soil characteristics and farming system. Options can include seeding techniques that concentrate water within the crop row, wetting agents and, where appropriate, soil amelioration practices such as claying, deep soil mixing, rotary spading or soil inversion.

Soil amelioration needs to be carefully matched to the soil and landscape. Deep cultivation can leave soil loose and exposed and substantially increase the risk of wind and water erosion if adequate groundcover is not quickly re-established. Managing soil water repellence should therefore be considered alongside other soil constraints and erosion risk.

Waterlogging occurs when soil in the plant root zone becomes saturated for long enough to reduce the oxygen available to plant roots. It can affect agricultural land in parts of the Northern Agricultural Region and may occur before water becomes visible at the soil surface.

Waterlogging develops where water enters the soil or landscape faster than it can drain away or be used by plants. Risk is influenced by rainfall, topography, soil type and drainage. Low-lying areas and soils with slowly permeable subsoils can be particularly susceptible.

Reduced oxygen in waterlogged soil restricts root growth and function, reducing plants’ ability to access water and nutrients. This can delay crop and pasture development, reduce productivity and, where waterlogging is prolonged or severe, result in plant death. Waterlogging can also interact with salinity and increase the impact of salt on susceptible plants.

Management depends on the cause, soil type and position in the landscape. Options may include maintaining or improving soil structure, managing surface water and runoff, using appropriate drainage systems or raised beds in suitable areas, and selecting crops, pastures or varieties better suited to waterlogging-prone land.

Water management should be planned at the paddock, farm and, where appropriate, catchment scale. Drainage needs to consider where water will be directed and the potential impacts on neighbouring land, waterways, wetlands and saline areas.