2.01 - Mapping pasture zones

1. Construct a plan that defines grazing land into pasture and cropping zones based on the limits set to determine the best options for establishing and managing pasture for optimum growth, quality and sustainability. The features and options for the various landclasses are shown in the following table adapted from NSW Agriculture.

Base the initial description of zones on physical properties of the landform and soil type that cannot be altered over time through management.

Further demarcate the zones based on major pasture growth or management limiting factors, such as occasional cropping, that can be changed over time but need to be factored into pasture species and fertiliser decisions. This includes saline affected areas or acid soils with high aluminium content.

Identify zones that are not adjoining but have similar characteristics and group them for farm planning purposes. Their identity should, however, be preserved to assist utilisation practice and analysis to ensure balanced growth, quality and species diversity across pasture based grazing lands.

* All pH measured by CaCl₂

Landclass 1 – very slight to negligible limitations, no special land management practices required

• Onsite impacts of land management practices are minor and may include some effects that can be readily managed such as nutrient depletion.
• Off site impacts of land management are minor.
• Prime agricultural land, capable of a wide variety of agricultural uses that involve regular cultivation.
• Have low slopes (<1%) with no erosion.
• Soils have sufficient clay content to inhibit wind erosion and offer some resistance to soil structure decline even under regular tillage.
• Land is free of rock outcrop and large stones that would restrict farm machinery operations.
• It has good drainage, with sufficient water holding capacity to supply growing crops and pastures.

Landclass 2 – slight but significant limitations – can be managed by readily available, easily implemented management practices

• Onsite impacts are slight – soil and land condition can deteriorate due to minor water and wind erosion.
• Off site impacts of land management are slight.
• Land is capable of a wide range of uses and management practices – cropping with cultivation, grazing, forestry, vegetables, horticultural production.
• Includes gently sloping land that is capable of a wide range of agricultural uses that involve cultivation.
• Can be subject to sheet, rill and gully erosion as well as wind erosion and soil structure decline.
• Limitations can be controlled by management practices – sowing with minimum disturbance, rotational grazing, maintaining windbreaks and groundcover in areas prone to wind erosion.
• Salinity can be a slight hazard due to deep drainage.
• Acidity can be a slight hazard.

Landclass 3 – moderate limitations – can be managed by more intensive management practices

• Onsite affects on soil and land condition can be moderate if limitations are not managed.
• Off site impacts of land management practices can be significant if limitations are not managed – salinity, leachate from acid sulphate soils, water erosion, water quality.
• Includes sloping lands (3–10%) that can erode when cultivated if runoff is not controlled.
• Included are lands that can be subject to wind erosion when cultivated and left bare.
• Land is capable of sustaining some cultivation on a rotational basis.
• Productivity will vary with soil fertility.
• Land can be subject to sheet, rill and gully erosion, as well as wind erosion and soil, structure decline.
• Severe soil erosion can be caused by regular cultivation without effective erosion control measures.
• Poor water quality can be caused by water erosion and dust storms may result from wind erosion.
• Wind breaks and ground cover should be retained in areas prone to wind erosion.
• Salinity can be a moderate hazard.
• Acidity can be a moderate hazard – soil acidity levels should be monitored and lime added.

Landclass 4 – moderate to severe limitations

• On site impacts on soil and land condition can be moderate if limitations not managed.
• Off site impacts of land management practices can be significant if limitations not managed.
• Includes sloping lands (10-25%).
• Land is generally used for grazing and is suitable for pasture improvement.
• Can be cultivated occasionally for sowing of pastures; however, it has cropping limitations because of erosion hazard, weak structure, salinity, acidification, shallowness of soils, stoniness or a combination of these.
• Erosion problems encountered include sheet, rill, gully and wind erosion.
• Ensuring plant growth is adequate to maintain evapotranspiration rates and maintain perennial pastures minimises salinity risk.

Landclass 5 – severe limitations

• On site impacts on soil and land condition can be severe if not managed.
• Off site impacts of land management practices can be severe if limitations not managed.
• Land only suitable for grazing – with some limitations.
• Includes sloping lands that can be severely eroded by runoff.
• Not capable of supporting cultivation due to a range of limitations including slope, soil erosion, shallowness and stoniness, or other limitations.
• Soil erosion can be severe without adequate erosion control measures.

Adapted from Land and Soil Capability – How we safely manage the land, Central West Catchment Management Authority, 2008.

2. Use the following observations and previous table and descriptions to define changes in landclass and capability. A new zone should be created whenever maximum acceptable limits are exceeded.

•  Soil texture class in A and B horizons. Refer to Tool 2.3 for methodology to assess soil texture. Create a new zone when texture changes more than one class, for example from sand to loam.

• Depth to impermeable layer and/or to subsoil layers with low soil pH as an indicator of potential rooting depth. Base initial assessments of soil depth on existing knowledge gained from digging post holes or soil pits and the presence of perched water tables. Then assess current pasture species and growth potential to identify shallow soils.
• Slope as an indicator of the risk of excess run-off and soil erosion. When available, use contour maps for precise measurement. Initially map out all land that you regard as steep and prone to higher rates of run-off. Look for evidence of soil erosion.
• Aspect as a measure of ambient temperature and its impact on grazing patterns, exposure to sunlight and degree of evapotranspiration. Separate north facing slope land from all others. South facing slopes can also have lower pasture production potential especially in combination with steep slopes and shading.
• Location of streams and naturally confined watercourse drainage lines.
• Soil salinity (EC) and acidity (low pH). Use the results of the comprehensive soil testing carried out for Procedure 3.
• Indicators of saline discharge areas and salt affected land (see Tool 2.4). This enables you to map out areas for reclamation for special stabilisation or reclamation treatment.
• Cropping or specialty fodders, such as lucerne, as the primary land use.

3. Use the mapped results to guide the development of infrastructure and to allow differential management of pasture zones. If the cost of changes to infrastructure is likely to be significant, conduct an economic assessment. Give highest investment priority to the management of identified fragile zones to ensure environmental protection is not compromised. The following are examples of fragile areas with recommended management approaches:

•  Riparian areas. Maintain a minimum of five metres of thickly grassed and unfertilised land along stream banks where water flows are likely to enter, and a minimum of 10m where periodic flows are likely.

• Problem aspects and slopes. Develop the capacity to differentially manage aspect to avoid overgrazing of warmer north facing slopes, undergrazing of cold south facing slopes, and landclasses 3, 4 and 5 to maintain high levels of ground cover, litter and pasture mass, especially during expected periods of high evapotranspiration, low soil moisture and risk of high intensity rainfall.
• Factors that limit pasture growth. Use species that are tolerant of any limiting factors. For example, use salt-tolerant species in saline discharge areas. Use species that tolerate long periods of soil saturation in zones prone to water logging as identified from indicator species and avoid grazing these areas while water logged.
• Natural features will affect grazing patterns and mustering ease.

4. Sources of planning assistance.

Whole farm planning packages are available from various agencies. Visit state agency websites (see Tool 2.5), or contact your nearest planning office.

• Mapping software is available from agricultural software suppliers (usually as part of farm database packages).
• Aerial photos (scanned if using computer mapping software). Use clear plastic overlays on aerial photos when the cost of mapping software is not justified.
• Commercially available contour maps of local area district (1:25,000 or better).
• Maps and photos are available from state planning and mapping authorities:
  • NSW – Land and Property Information, 1300 052 637, www.lpi.nsw.gov.au
  • Tasmania – Service Tasmania, (03) 6233 2654, www.tasmap.tas.gov.au
  • South Australia – Mapland, (08) 8463 3999, www.environment.sa.gov.au/Do_It_Online/Mapland
  • Western Australia – Landgate, 1300 556 224, www.landgate.wa.gov.au