Use of CaCl2 to decrease ammonia volatilization after application of fresh and anaerobic chicken slurry to soil

Abstract

SUMMARYAmmonia losses after surface application of fresh chicken slurry (15% solids) and anaer‐obically stored chicken slurry (10% solids) to a silty clay soil (pH 6.9) at a rate equivalent to 34 m3 ha−1 were studied in a laboratory incubation experiment. Total NH3‐N losses amounted to 29% of the initial uric acid‐N+urea‐N+NH+4‐N content of the fresh slurry and 28% of the initial NH+4‐N content of the anaerobic slurry. Peak rates of ammonia volatilization took place between 24 h and 48 h after application of the fresh slurry and within 5 h of application of the anaerobic slurry. The addition of CaCl2 at a rate of 36 mg Ca g−1 (dry wt) slurry decreased peak rates of ammonia volatilization from the fresh slurry by 73% and total losses by 37%. The decrease in total ammonia losses through CaCl2 addition to the anaerobic slurry was only 8 %. The addition of CaCl2 decreased CO2 output from both slurries through precipitation of HCO3− as CaCO3, thereby removing a source of alkalinity from the solution. The failure of the CaCl2 addition to decrease significantly ammonia losses from the anaerobic slurry suggested that HCO3− was an important source of alkalinity driving ammonia volatilization in the fresh slurry, but not in the anaerobic slurry.CaCl2, addition did not affect urea hydrolysis, nor net nitrogen mineralization. The decrease in ammonia loss achieved through CaCl2 addition was however not associated with a parallel increase in ammonium concentrations in the soil. Further experiments showed that the ammonia retained by the CaCl2, was probably fixed by the soil and rendered non‐extractable by KCl.