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Rachman et al.

DYNAMICS OF TSUNAMI-AFFECTED SOIL PROPERTIES Achmad Rachman1, I G. M. Subiksa1, Deddy Erfandi1 and Peter Slavich2 1 Indonesia Soil Research Institute, Jl. Ir. H. Juanda 98 Bogor 16123 Indonesia, 2 NSW Department of Primary Industries, 1243 Bruxner Highway, Wallongbar NSW 2477 Australia

Abstract Seawater inundation after the tsunami on December 26, 2004 changed the soil chemical properties of agricultural land along the coastal areas of Aceh, Indonesia. It was approximated that 90,000 ha of paddy fields, 25,000 ha of mixed gardens, and 90,000 ha of estate crops were inundated. The objective of this study was to study the changes in soil chemical properties on the selected areas affected by the tsunami and access constraints to crop performance. Twenty monitoring sites have been established to regularly assess soil chemical properties and crop performance. Crops which have been assessed include rice, corn, peanut, soybean, onion and chillies. At each site, composite soil samples were collected from 4 depths at 20 cm interval for selected soil chemical analyses. The level of soil salinity in tsunami-affected areas appears to be related to the duration of inundation by the sea water and the permeability of the soils. Soils that were inundated for up to 6 days after the tsunami appear to be more saline compared to those inundated for only 1-3 days. In most areas, soil salinity has returned to normal levels within less than one year period especially in areas with relatively high rainfall, sandy soils or peat soils. However, in areas where lateral water flows are prevented by damaged drainage systems, salinity is still too high for most crops (ECe>4 dS/m). Where farmers had access to irrigation water, the vegetative growth of rice crops established after the tsunami appeared unaffected, but grain formation has been severely affected causing up to 50% yield loss. The lack of grain formation on rice and empty pod of peanut appeared to be related to high soil salinity that cause osmotic stress and nutritional imbalance. The low Ca/Mg and K/(Ca+Mg) ratios, 27 mg/kg P), high potential potassium (200 – 2560 mg/kg), and high exchangeable Ca, Mg, K, and Na. The ECe ranged from 19,8 dS/m in Mire Aceh Besar to 84,2 dS/m in Keneuneu Aceh Besar. These mud characteristics suggest that there is a potential for nutrient enrichment into the soil. However the muds were highly saline so the benefits of these nutrients would only become available once the soluble salts have been flushed from the field. Soil salinity is an important growthlimiting factor for most non-halophytic plants. Soil samples collected from a filed where paddy field dominated the landscape had higher salinity level as compared to a filed where dry land agriculture dominated the landscape (Figure 1). The paddy field tended to hold deposited mud inside the bunds, therefore, increased the chance to elevate soil salinity, while in the dry land, the heavy rain received after tsunami had washed off the salts in soils. In addition, results showed that top soils had more salt concentration that subsoils. The EC for the top soils had been elevated from