Bart Schultz
The country has a tropical climate, with rainfall patterns influenced by monsoon winds from the Indian Ocean and the Bay of Bengal. Tropical cyclones occasionally bring rain to the southwest, northeast, and east of the island.
The country has extensive lowland areas and several polders. An area of approximately 70,000 hectares, the vast majority of which has been reclaimed, is prone to flooding. The Muthurajawela polder, covering approximately 2,450 hectares on the west coast, is one of the largest. The polder is traversed by a channel known as the Old Dutch Canal. This canal originated in 1767 when the area was reclaimed at the initiative of Iman Willem Falck, then the Dutch governor of Ceylon (the former name of Sri Lanka).
In the following years, several attempts were made to reclaim the area, but usually with little success, as acidic sulphate soils (in Dutch known as "katteklei", which means "cat clay") often developed.
Acidic sulphate soils are a well-known problem with land reclamation projects in humid tropical lowland areas. As long as these types of soils remain underwater, there's little to worry about. However, if they are reclaimed and the groundwater level is lowered - allowing oxygen to enter - they can become extremely acidic, making them virtually uncultivable. The problem with this is that it can take decades for the acids to be washed away and the soils to become suitable for agriculture. Only with very careful water management, where the groundwater level is only lowered when there are no crops on the land, is agriculture possible on these soils, even in the initial stages. However, yields are then lower than in the final situation.
One of my PhD students once developed a method based on a computer model to accelerate acid leaching. During crop growth, the groundwater level was kept high, and during the rest of the growth period, it was kept as low as possible, thus accelerating acid leaching. While the soil improvement was faster, it still took several years before the soil was suitable.
Besides the Muthurajawela polder, several other polders in Sri Lanka are worth mentioning. These are: Karavaku (810 hectares), Kiralekele (972 hectares), Thampalakaman (81 hectares) in the Mahaweli River delta, and Thondamannar (2,000 hectares). I don't know to what extent acidification has also been a problem in these polders.
