Credit for the photos: Ahmed Shaheen (Egypt)
Review: Abdel Rahman El Gamal (Founder of the website)
A relatively recent farm survey (NACA, 1996) revealed that about 90% of Thai shrimp farmers spray lime to tackle the low pH associated problems especially those related to health and survival of farmed shrimp.
The application of lime is done to correct the soil pH and stabilize water pH. Moreover, lime is also applied to disinfect the pond and control disease (especially external parasites), while a secondary effect of liming is the release of trapped nutrients that become unavailable under acidic conditions. Liming is of particular importance in shrimp farms which were constructed on previous mangrove areas whereas acid sulphate soils are common in these farms. Liming of shrimp ponds is usually done prior to stocking and occasionally during the grow-out season.
Lime is spread evenly over pond bottom, and also spread along dikes and water supply canals as shown in the photos. The four types of lime used in Thailand are “agricultural lime”, “hydrate lime”, “quicklime”, and “dolomite”. Even though, the use of particular type(s) of lime is favored over others in specific situations, lime quantities used are often based on accumulated experiences with few cases on laboratory analysis and recommendations. It could be said that the agriculture lime is used in relatively large quantities compared to other types of lime. For guidance only, the recommended quantity of agricultural lime (CaCO3) is 1-2 ton/ha when soil pH is higher than 6, and 2-3 tons/ha when the soil pH ranges from 5-6, and 3-4 tons/ha when the soil pH is lower than 5.
In general, lime requirement for clay soil is higher than that for sand. This is due to the low porosity of clay, the presence of acid producing minerals, and to the higher concentrations of pyrite that continues to release acid. It may worth mentioning that excessive use of lime that could lead to high water pH which in turn makes ammonia more toxic to farmed shrimp.