Achmad Rachman, Subikse, Deddy Erfandi and Peter Slavich
Seawater inundation after the tsunami on December 26, 2004 has changed 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 mix 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 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 appears to be more saline compared to those inundated for only 1-3 days. In most areas, soil salinity has returned to normal level 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 is 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, <5 for Ca/Mg ratio and <0.04 for K/(Ca+Mg) ratio, may have caused low P and K availability for plant uptake. Farmers are encouraged to apply inorganic fertilizers, especially potassium and phosphorus besides nitrogen, and organic matter from crop residues and manures to improve nutrient and water holding capacity of soils; improve soil structure to allow effective root development for non-rice crops.