What Remote Sensing (Optical) can tells us about Salinization
James Cook University
School of Environmental and Earth Science
With the current growth population, the production of food is critical for future survival. To produce high quantities of food, we need fertile soils and keep them fertilize. Soils are the most important resource in earth. Quality soils vary and we need to classify them and protect them. In situ qualification is slow and expensive. Advances in remote sensing gives the opportunity to assess soil in large scale in remote areas and monitor changes easily and cheaply compare to field-testing. One of the biggest dangers to soil fertility in Australia and the world is soil erosion. Erosion degrades soils, however its long terms effects can be more severe than short-term effects like crop productivity loss (Rengasamy, 2002).
Soil erosion needs to be monitored specially salinization. In Australia and the world salinization is a major source of degradation. There are 230 million ha of irrigated land in the world, and 45 million ha of those are salt-affected (19.5 percent) and of the 1,500 million ha under dry land agriculture, 32 million are salt-affected to varying degrees (2.1 percent) (Rengasamy, 2002). Careful monitoring of soil salinization is needed to reduce degradation and protect sustainable land use and management.
Salinity is a natural process that occurs when dissolved salts accumulate in soil water, this affects plant growth and a way to monitor soil degradation with emphasis on salinization is through the use of remote sensing techniques. Remote sensing with technological improvements in the last decade is becoming important and a valuable tool. Remote sensors are quick instruments that can be used to identify and produce map soils checking their degradation. Airborne geophysics and ground based-electromagnetic induction meters combine with ground data have shown potential for mapping depth of salinity occurrence (Metternicht, 2003). Even though the advances in remote sensing in the last decade had improved greatly, still is not a substitute for field data collection. Discussion
In the past Australia has suffered from salinization. Creating saline and sodic soils in the present time (Northcote and Skene, 1972). Salinity and sodicity of the soil, reflects the balance between hydrology, soil properties and vegetation. This balance depicts the agricultural potential of the area and where salinity may be an issue.
Salinity can occur naturally (figure 1) or man made (figure 2), it reduces and even prohibits plant growths. Plus it can cause soil dispersion, increase soil erosion and engineering problems. Salinisation has increase dramatically in Australia due to man mismanagement of the land. Figure 1: Natural salinization process before and after clearing Source: "Water: A Finite Resource," 1995, http://www.fao.org/docrep/u8480e/u8480e0c.htm
Secondary salinisation cost in Murray-Darling Basin in Australia was estimated at US$ 208 million per year (Ghassemi et al., 1995). This cost regularly do not count property loss of farm land value due to land degradation, plus other effects like eutrotiphication of rivers and estuaries, and
road damage, building or other infrastructure. Australia (National Land and Water Resources Audit, 2000) calculates around 20,000 km of major roads and 1,600 km of railways at risk of damage due to salinization.
Salt come from many sources, for example; Salt has accumulates since early times in parental material, when it rains or other form of weathering the salt leaches out, this happens specially in warm climates. Another for of salt movement is through...