REDUCING AMMONIA LOSS FROM CATTLE SLURRY BY THE USE OF ACIDIFYING ADDITIVES - THE ROLE OF THE BUFFER SYSTEM

An 8-month-old cattle slurry was analysed titrimetrically and the major buffer components were found to be ammonium, bicarbonate and a solid phase of carbonates. A simulation model was developed which explained the experimental results. pH stability in response to addition of HCl, superphosphate, FeCl3, Ca(NO3)2 and CaCl2 in increasing levels was investigated. Upon aeration, pH rose quickly by 0.4 to 1.5 units for all additives and levels, except where HCl was added equivalently to the total alkalinity of the slurry, which then kept a stable pH of 4.2. Ammonia volatilisation in response to the addition of either HCl or CaCl2 was found to decrease with increasing amount of additive, HCl being more effective than CaCl2. This confirms that the total alkalinity is an important factor regulating the potential ammonia loss from cattle slurry. Addition of HCl or CaCl2 close to the total alkalinity resulted in a reduction of the potential ammonia loss to 0 and 15% of the untreated loss, respectively.