The College of Agriculture, Food, and Rural Enterprise (CAFRE) has said that using lightweight expanded clay aggregate (LECA) as a slurry store cover can reduce reduce ammonia emissions by 60% compared to stores with no cover.
CAFRE said it had recently added LECA to its uncovered above-ground slurry stores at its Hill Farm Centre in Glenwherry.
Air technologist at CAFRE, Stephen Gilkinson said: “LECA is naturally produced clay sphere aggregate that is 1cm in size.
“The purpose of the product is to reduce ammonia emissions from uncovered slurry stores. Applying LECA to uncovered slurry storage at Greenmount Campus will lessen the likelihood of ammonia deposition on nearby sensitive environmental sites.”
LECA product comes in large 2.2m3 bags and is applied to a store with a long reach telescopic handler and emptied via a pull cord from ground level.
The LECA spheres find their own level, with a recommended application depth of 10cm.
The amount of product needed is calculated by multiplying size of the store in square metres by 0.1, which will result in a 10cm layer volume. This value is then divided by the volume of the bags to give the number required for the store.
On installation, the Hill Farm Centre tank held a 300mm minimum depth of slurry and was thoroughly agitated with no surface crust.
A naturally occurring crust can reduce ammonia emissions, but this is largely dependent on thickness and may not readily form due to tanks being mixed.
CAFRE said there are a number of options available to mitigate ammonia emissions from stores, such as impermeable covers – which are mandatory for new covers – floating covers, and hexa tiles.
The cost of LECA will vary depending on the surface area of the store; however, a rough guide is £330/bag based on CAFRE’s installation amounts.
CAFRE advised those using LECA to not agitate the tank during extraction to avoid spheres being drawn into the pump system.
When extracting, farmers should ensure that a vortex does not develop above the outlet (which is generally from 200mm to 450mm above the outlet, but can be higher), as this will also draw LECA product into the pumping system.
