Bentonites and layered double hydroxides can decrease nutrient losses from spent poultry litter

Manure by-products of intensive livestock industries, such as spent poultry litter are a considerable nutrient resource. This study sought to improve the environmental characteristics of spent poultry litter, through the addition of hydrotalcite and bentonite, to decrease likely nutrient losses to the environment.Three experiments were conducted. An incubation trial sought to identify the effect of bentonite addition (0 to 158% m/m of dry spent-litter mass) on exchangeable retention of ammonium-N in poultry litter. A column leaching trial (33 pore volumes over 11 days) sought to determine the effect of varied hydrotalcite additions (0 to 50% m/m) and a fixed rate of bentonite (127% m/m) on phosphorus release. Rainfall simulations were conducted on turf-applied spent poultry litter to determine the effect of alum (0 to 11% m/m), bentonite (0 to 158% m/m), and hydrotalcite (0 to 50% m/m) addition on overland losses of phosphorus.The addition of bentonite (0 to 158%) increased the proportion of mineral N retained in exchangeable form from 19% to as much as 54%. The additions of hydrotalcite at 30% of the mass of dried litter resulted in 90% decreases in the quantity of phosphorus leached. However, under rainfall simulation, the 10% hydrotalcite addition combined with bentonite (127%) was sufficient to effectively eliminate run-off phosphorus losses that occurred with untreated spent litter. The combination of hydrotalcite (10%) and bentonite appeared to exceed the performance of conventional rates (2 to 11% m/m) of alum addition. Only a small proportion of the decrease in phosphorus losses was attributable to bentonite addition.

Research Highlights
► 10% hydrotalcite addition to spent poultry litter eliminated run-off phosphorus.
► 30% hydrotalcite addition to poultry litter decreased phosphorus leaching by 90%.
► Bentonite treatment increased the proportion of exchangeable mineral N.
► Hydrotalcite + bentonite out-performed conventional rates (2 to 11%) of alum treatment.