Previous PageTable Of ContentsNext Page

Catchment Management – the relevance of soils in management and planning.

A.J.E. McGaw, R.G. Banks, H.B Milford, G.A. Chapman, C.L. Murphy, K.J. Nixon, J.A. Edye and N.A. Simons

Resource Information Systems
Department of Land and Water Conservation
PO Box 3720, Parramatta, NSW 2124
(Phone) 02 9895 6204, (Fax) 02 9895 7985


The disturbance of soil by land use impacts on the quality of our environment. Salinity, soil acidification and erosion are some of the problems. These impacts can also cause financial and ecological losses.

Soil landscape maps and soil profile information provide an understanding of the formative processes of the soils and landscapes and their qualities and limitations. Soil landscape mapping is routinely used to determine capability of lands for particular uses before or in tandem with developing industries.

Soil landscape information is also being used to model environmental and financial factors for optimised land use and to address land degradation problems in a profitable and sustainable way. For example, on the Liverpool Plains soil landscape information has been combined with deep drainage research data, to develop a sustainable land use plan that presents both the most sustainable and profitable land uses for each landscape. Catchment wide changes are most likely to occur with precise and prescriptive recommendations, which can stabilise or increase farm income. Soil landscapes have provided the vehicle for spatially managing catchment wide change.

Understanding the distribution and capabilities of various soils and landscapes is an important part of ensuring a stable, productive and sustainable catchment. Soil Landscape Maps can precisely indicate where new or changed industries will help maximise productivity in a sustainable way.


The general purpose of collecting soil information is to "study, classify, describe and map soils so that predictions can be made about their behaviour for various uses and their response to defined management systems" (USDA, 1950).

The collection of soil data from general NSW soil survey (Department of Land and Water Conservation Soil Landscape Mapping program), which is stored in the NSW Soil and Land Information System (SALIS), can be used for many purposes well beyond those for which it was originally collected. Example of derivative products used in soil management and planning are Soil Landscape Mapping for sustainable and profitable salinity control planning – Case study – the Liverpool Plains and the production of soil point source maps for the Catchment Management Boards.

Using Soil Landscape Mapping for sustainable and profitable salinity control planning – Case study – the Liverpool Plains.


Salinity in the highly productive Liverpool Plains is recognised as a major threat to agricultural production and ecosystem health. As such the Liverpool Plains has been a focal catchment in NSW for salinity research and for setting precedents for determining drainage friendly land uses which are profitable and sustainable. Soil landscape mapping has been used to identify soils and landscapes, which contribute to the salinity problem in the region, and to target research and extension of research.

Modelling was carried out using the CSIRO Agricultural Production Systems Simulator (APSIM) and was based on soil data collected during soil landscape mapping and measured deep drainage under different permutations of land use practices. The results have been used to predict the most profitable and sustainable land uses for the agricultural and grazing lands of the Liverpool Plains.


123 soil profiles were chosen out of the large data set available for the Liverpool Plains. The profiles where sampled for Bulk Density and onsite saturated hydraulic conductivity (Ksat) measurements where determined. At two key research sites, on representative regionally dominant soils, NSW Agriculture measured the deep drainage occurring for as many as 40 different permutations of different representative land use types over 5 years. These results were used to calibrate APSIM so that deep drainage values could be determined for the whole suite of representative soils in the Liverpool Plains under different land use practices. This was done by running the model using 40 years of real rainfall data, for different areas of the Liverpool Plains.


Findings were basically that the practice of long fallowing on plains and footslopes dominated by Vertosols was very ‘leaky’ regardless of crop type (Figure 1). In terms of the most cost-effective ways to respond to these results, APSIM modelling showed that response cropping, or sowing crops when there is approximately 60 cm of stored soil moisture, will almost emulate pasture and tree water use on these lands. This means that back to back summer cropping becomes a viable option for many areas, reducing the need for an eighteen-month fallow between crops and avoiding deep drainage.

Figure 1: Land Use practices and deep drainage on vertosols.

On the plains and footslopes dominated by Red Chromosols (and to a lesser extent Sodosols), no type of cropping practice effectively reduced deep drainage (Figure 2). Pasture based land use is the recommendation for these lands, with occasional cropping (1 year in 4 – 7).

Figure 2: Land Use practices and deep drainage on Chromosols and Sodosols.


Having determined profitable and sustainable ways of avoiding deep drainage, soil landscape mapping has been used to extend the results of the modelling (Figure 3). Land use recommendations or drainage values can be attached to soil landscape polygons to produce a map of appropriate land use at a paddock scale showing where changes can be implemented and what their effect will be.

Figure 3: Profitable Land Use Practices for Deep Drainage Control.

This data is now the basis for a broad-scale process of land use change that should be profitable for all. This study has been an innovation in the management of salinity in that the ‘plant trees’ response has not really been considered as an option, although the effect of tree planting has been modelled as part of this study. The most important result of this work is that we can show not only where land use needs to change but we can also demonstrate that it is almost immediately profitable for many land owners to make such changes. If this is the case then landholders are not left with the perception that they are investing money and time and Government funds in fixing someone else’s problem.

Soil Point Maps for Catchment Management Boards


Data from over 31,000 profiles in SALIS was used to produce six maps for the Catchment Management Boards. The maps show Inherent Sheet Erosion Risk, Salinity, Surface Soil pH, Surface Soil Acidification Hazard, Wind Erodibility and Sodicity. The maps identify point source data that has been described, sampled and/or tested and recorded in SALIS.

The information contained on the maps will assist Catchment Management Boards to assess and rate the extent and importance of various soil issues within the Catchments. This information could also be used to justify the allocation of resources for addressing key issues. This could well include the direction of individual projects/resources towards rectification of specific causes of a Catchment's natural resource problems.

Inherent Sheet Erosion Risk Map

Inherent Sheet Erosion Risk (ISER) is the long-term susceptibility of a parcel of land to sheet and rill erosion if the soil is left bare and no erosion control management is being used in tonnes of soil per hectare per year (Rosewell et al., 1988). Figure 4 shows an example of this type of map.

Soil erosion is a major land degradation issue in Australia, as it depletes productivity in soils that are already marginal and will make them completely worthless in the long-term. Soil loss of greater than ten tonnes per hectare per year is considered to be unacceptable for deep, fertile soils. This figure is lower for shallow, infertile soil. The main causes of soil erosion are cultivation, overgrazing, clearing and land use change.

Figure 4: Inherent Sheet Erosion Risk in the Murrumbidgee Catchment Management Board Area.

Soil Salinity Map

Saline soils generally have a high erosion hazard, are often poorly drained and are toxic to most plants. Figure 5 shows areas of salinity in the Murrumbidgee Catchment Management Board Area. The soil salinity map shows areas where salinity has been observed at the soil surface and where soil tests results have indicated salinity in the soil profile.

Figure 5: Salinity in the Murrumbidgee Catchment Management Board Area.

Surface Soil pH Map

pH is a measure of acidity and alkalinity. Technically it is the negative log of the concentration of hydrogen ions in a solution. Figure 6 shows an example of this type of map for the Hunter Catchment Management Trust Area.

Acidity - Extremely or strongly acid soils have a pH values less than 5.5 in 1:5 Soil:Water. Acid soils are often leached of many soluble ions and are commonly deficient in major plant nutrients such as calcium, magnesium, nitrogen, phosphorus and molybdenum. Metal ions, such as aluminium and manganese may also be soluble in toxic concentrations. Whilst many native species are tolerant of acid conditions, those that are not tolerant may require heavy applications of lime or dolomite to raise the pH (and nutrient supply) to a satisfactory level.

Alkalinity - Alkaline soils are those that have pH values greater than 8.5 in 1:5 Soil:Water. Soil alkalinity reduces the availability of some essential plant nutrients such as iron, manganese, copper, cobalt and zinc and as such may inhibit the growth of plants.

Figure 6: Surface Soil pH in the Hunter Catchment Management Trust Area.

Surface Soil Acidification Hazard Map

Surface soil acidification hazard is the amount of acid added to bring soil pH to critical level. Critical soil pH is considered to be 5.5 in 1:5 soil:water, below which aluminium becomes increasingly soluble and toxic to plants (Isbell 1996), thus limiting the types of crop and pasture that can be grow. Figure 7 shows an example of this type of map for the Hawkesbury-Nepean Catchment Management Trust Area, where the risk of acidification of the soil is high. Soils with a high acidification hazard should be carefully managed.

Figure 7: Surface Soil Acidification Hazard in the Hawkesbury-Nepean Catchment Management Trust Area.

Soil Sodicity Map

Sodic soils contain sufficient exchangeable sodium to adversely affect plant growth, are prone to dispersion, and are often highly erodible with low wet bearing strengths. Sodic soils are also relatively impermeable to water, thus reducing productivity through lack of available soil moisture and increasing run-off and erosion. The map of sodic soils shows locations where at least one soil layer has been shown by soil testing to be sodic or belonging to a sodic Great Soil Group. Figure 8 shows an example of this type of map for the Murrumbidgee Catchment Management Board Area, where there are considerable problems with sodic soils.

When they are dry, sodic soils are often dense and hardsetting. Since sodic soils collapse when wet, surface sealing and crusting often inhibits seedling emergence. Sodic soils are prone to soil structure decline and require careful management.

Figure 8: Soil Sodicity in the Murrumbidgee Catchment Management Board Area.

Surface Soil Wind Erodibility Map

Wind erodibility is the inherent propensity of bare and dry soil to be caught up and transported by wind. Wind erodibility is independent of site conditions such as climate, vegetative cover or surface roughness. Wind erosion can be avoided or minimised by following recommended land management practices. Figure 9 shows an example of this type of map for the Murrumbidgee Catchment Management Board Area.

Figure 9: Surface Soil Wind Erodibility in the Murrumbidgee Catchment Management Board Area.


These maps have helped the Catchment Management Boards to consider the extent and magnitude of soil issues within their catchment and instigate projects that will address the major issues.

Understanding the distribution and capabilities of various soils is an important part of ensuring use in a productive manner that is sustainable well into the future. Many soil degradation processes can be somewhat difficult to directly observe, which means that they are often overlooked and ignored. Yet many of these processes need to be properly and directly addressed if we are to have healthy and sustainable catchments.


Stable and healthy soils are vital in the production most of our food and fibre and as such can be considered our most valuable non-renewable natural resource. By using landscape and profile information to better understand our soils, we can better manage their use and avoid the degradation of a resource that is very slow to form. Soil degradation is often difficult and costly to reverse but is preventable with appropriate land use and management.


Isbell R.F. (1996). Australian Soil and Land Survey Handbook: The Australian Soil Classification, CSIRO, Australia.

Rosewell, C.J. and Edwards, K. (1988). SOILOSS: A Program to Assist in the Selection of Management Practices to Reduce Erosion, Technical Handbook No. 11, Soil Conservation Service of NSW, Sydney.

USDA (1950). Handbook of Soil Survey Investigation: Field Procedures, United States Department of Agriculture.

Previous PageTop Of PageNext Page