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State of the
Environment 2000 - Land Condition and Hazard Maps
Materials, methods and conclusions The NSW State Government produces State of the Environment (SoE) reports every three years to help monitor its land management objectives. The latest SOE reports are available from the Department of Environment and Conservation website, which includes the most recent 2003 SOE report. The soil and landscape information contained within the SoE reports come from general NSW soil survey records (Soil Landscape Mapping program) that are output through the Soil and Landscape Information System (SALIS). They also contain substantial amounts of information collected by soil scientists for many other purposes. The 2000 report was the first time in NSW that routine soil information from a point source database had been used for providing spatial views of soil information for the SoE report. The outputs indicated the best possible representation of the state of the soils environment in NSW. The following information relates specifically to the 2000 report. [Top] Materials, methods and conclusions Maps of each theme were produced and analysed, but there are many places in NSW where no formal record of measured soil attributes exists. This can be seen in the large blank areas shown on the maps. Knowledge of the condition of our soils is far from complete, but the NSW Soil Landscape mapping program continues to fill in the blanks. Data from over 31,000 profiles in SALIS was used to produce the six maps for the SoE 2000 report. The maps show Surface Soil Wind Erodibility, Inherent Sheet Erosion Risk, Salinity, Surface Soil pH, Surface Soil Acidification Hazard, and Sodicity. They identify point source data that has been described, sampled and/or tested and recorded in SALIS. [Top] Wind erodibility is the inherent propensity of soil to be entrained and transported by wind. Wind erodibility is independent of site conditions such as climate, vegetative cover or surface roughness. Wind erodibility is measured using a nine-class soil classification, based on the soil's resistance to wind erosion in cultivated areas (USDA 1993). Wind erodibility group allocation is based on soil texture, organic matter, calcium carbonate content, rock content and aggregate stability. Wind erodibility is high at 13% (3710 profiles) and moderate at 46% (13031 profiles) of the profiles recorded in SALIS. This indicates that there is a potential for large-scale loss of topsoil through wind erosion in NSW. View map. Inherent Sheet Erosion Risk (ISER) is the long-term susceptibility of a parcel of land to sheet erosion if the soil is left bare and no erosion control management is employed. ISER is a function of the intrinsic attributes of the land that contribute to potential soil loss (in tonnes of soil per hectare per year) including rainfall erosivity, topsoil soil erodibility and slope gradient, if there is no protective vegetation (Rosewell & Edwards 1988). Soil loss through sheet erosion of over 100 tonnes/hectare/year is predicted at 31% (5139 profiles) of the sites in SALIS. Such erosion would result in large-scale removal of topsoils and sedimentation of streams. View map. Saline surface soils are usually bare or have sparse plant cover. Saline soils have a high erosion hazard, are often poorly drained and are toxic to most plants. Three information sources have been combined to show land that is or has previously been effected by salinity. The sources are 1) soil profiles where surface expressions of salinity were recorded in the field; 2) soil samples where electrical conductivity in 1:5 soil:water was measured in the laboratory (electrical conductivity in 1:5 soil:water was converted to estimated electrical conductivity in saturated extract using the estimated clay percentage); and 3) Sodic and saline Great Soil Groups on the basis that sodic soils have previously been saline (Fitzpatrick et al. 2000). The Great Soil Groups include Solonchaks, Solonetz, Soloths, Solodized Solonetz and Solodic Soils (Stace et al. 1968). Salinity has been identified in the field at 3% (822 profiles) of locations where data is available. The lab data recorded in SALIS shows that 10% (744 profiles) of results are extreme, very high or highly saline. Such results suggest a reduction in plant growth. (It should be noted that there are significant problems with salinity in NSW that are not accurately shown by these results. This is due to limited data availability. View map. pH is a measure of acidity and alkalinity. Technically, it is the negative log of the concentration of hydrogen ions in a solution. 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 may also be soluble in toxic concentrations. Excessive soil alkalinity reduces the availability of some essential plant nutrients such as iron, manganese, copper, cobalt and zinc. Soil sample test results for surface soils that have both field and laboratory pH measurements were regressed and the relationship between Raupach, 1:5 soil:water and 1:5 0.1mol CaCl2 was established. The pH results in SALIS show that 90% (22484 profiles) of the sites are acidic (pH < 6.5) and 2% (473 profiles) are alkaline (pH > 7.5). Acidity and alkalinity may both result in a reduction of plant growth due to trace element deficiencies and toxicities. View map. Surface Soil Acidification Hazard Surface soil acidification hazard is the amount of acid that needs to be added to bring soil pH to critical level. Critical soil pH is considered to be 5.5 in 1:5 soil:water because below this pH level aluminium becomes increasingly soluble and toxic to plants (Isbell 1996). An equation using clay percent, organic carbon content and pH 1:5 Soil:Water (Bui 1998) was used to calculate acidification hazard. Of the profiles recorded in SALIS 35% (8688 profiles) are below the critical level of 5.5 and 33% (8153 profiles) are at a high or very high risk of reaching the critical level. Making their management important to avoid reaching the critical level and subsequently limiting plant growth. View map. A sodic soil contains sufficient exchangeable sodium to adversely affect plant growth and soil stability. Many sodic soils are sodic because they have been saline (Houghton et al. 1986). As the salt leached away some sodium remained attached to cation exchange sites on negatively charged soil particle surfaces. Today the sodium remains and these previously saline soils are still sodic. Sodic soils are prone to dispersion, are often highly erodible and have low wet bearing strength. Sodic soils are also relatively impermeable to water, reducing productivity and increasing run-off and erosion problems. When dry, sodic soils are often dense and set hard. As sodic soils collapse when wet, surface seals and crusts often inhibit seedling emergence. Sodic soils are prone to soil structure decline and require careful management. Exchangeable sodium percentages where calculated were laboratory test results were available. Great Soil Groups were also used to identify sodic soils. The results in SALIS show that 15% (1130 profiles) of the sites recorded with sodicity are strongly or very strongly sodic making them highly susceptible to dispersion, highly erodible, low wet bearing strength, impermeable to water, reducing productivity and increasing run-off and erosion problems. View map. [Top]
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Last modified: 14/09/2005 |
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State
of the Environment 2000 - Land Condition and Hazard Maps