Effects of 2004‐tsunami on the changes from 2005 to 2006 in salinity of soil profiles and groundwater wells and on mortality of garden fruit trees in Maldives

Most of the islands in the Republic of Maldives with an average elevation of 2 m above sea level was under the water during the 2004‐Tsunami. The objectives of this study were to assess the extent of damages to garden fruit trees in Maldives and their relative tolerance to salts after a tsunami on December 26, 2004, to assess initial salinization and residual salts in the soil and groundwater wells after the first monsoon, and to formulate practical field treatments to restore the health of salt‐affected fruit trees. After a series of four visits to 13 islands in Maldives in March, April, July, 2005, and February, 2006, it was found that majority of the salt‐sensitive fruit trees (mango, guava, and bilimbi) were killed or severely damaged, some intermediate‐tolerant trees (breadfruit, and corkwood) survived with some damages to shoots, sprouting species (banana and papaya) recovered with new shoots after initial shoot die‐back, moderately tolerant trees (areca nut, pond apple, screw pine, and drum stick) received less damages, and tolerant trees (coconut and sea hibiscus) had no damages. Salinization of soils was extensive in most of the local soils over‐topped by the tsunami. Electrical conductivity (EC) of soil profiles in some of the islands was 2.37 dS/m in average (range: 0.14–11.98 ds/m) in March, 0.36 dS/m in July, 2005 and 0.32 dS/m in February, 2006, suggesting that some salts were washed down from the soil profiles after the beginning of monsoon in May, 2005. Most of the soils would be suitable for annual crops with shallow root systems, while garden fruit trees with deep root systems would be adversely affected if the root tips hit the salty groundwater. The groundwater table in these islands was very shallow and had an average of 80 cm in the middle of a dry season in March, 2005. The EC of groundwater wells in some of the islands was 5.3 dS/m in average (range: 0.54–14.69 dS/m) in March, 4.06 dS/m in July, 2005 and 2.52 dS/m in February, 2006, suggesting that groundwater wells were still severely contaminated with salts even after the first monsoon in 2005 with a total precipitation ranging from 1,400 to 1,900 mm. Most of the groundwater wells were still salty in February, 2006 and were not suitable for drinking or irrigation. It was expected that additional monsoon in 2006 might further wash out salts from the soil profiles and might further dilute the groundwater wells to a level that might be safe for temporary irrigation, but not for drinking purpose. Stem injections that contained some minerals, vitamins, and plant hormones applied to salt‐affected mangos and breadfruits in March, 2005 failed to rescue the treated trees, possibly due to delayed late injections and a continued dry season for five months after the tsunami.

Key words:

• salinization
• salt residues
• salt tolerance
• electrical conductivity
• stem injection
• coconut
• sea hibiscus
• mango
• breadfruit
• guava
• banana
• papaya

Notes

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