Effects of wheat straw and spruce sawdust on the decaying of urinary nitrogen in the presence of urease.

The fate of urinary nitrogen from cattle urine has been carried out during 7 days by measuring daily the concentration of ammonium and nitrate. The pH has been also performed. The experiments were conducted into polyethylene bags (1l, each) containing a buffered aqueous solution (pH 7.50), with 2 ml/l of cat tie urine and 20 IU/I of urease. This solution was allocated into 4 trials (S1; S2; S3; S4) splited in triplicate. The bags were placed into water bath maintained at 24-26 degrees C and continuously aerated. Nitrifying bacteria were added to the bags of 3 of 4 groups and wheat straw (10 g/l) or spruce sawdust (10 g/l) has been added to 2 of these groups. The solution with urine + urease (S1) showed a rapid increase of the concentration of ammonium after one day, and remained constant throughout the experimental period. Moreover, no nitrate accumulation was observed. The solution with urine + urease + nitrifying bacteria (S2) also induced an increase of the concentration of ammonium, followed, after one day, by a decrease of ammonium concentration with increasing of nitrate concentration. No consistent increase in ammonium and nitrate concentrations was found when the solution was incubated with wheat straw (S3). In contrast, the solution with spruce (S4) induced an increase of ammonium and nitrate concentrations. However, the rate of nitrate formation from S4 remained lower than that observed with S2. The nitrate formation recorded in trials S2 and S4 induced a decrease of pH significantly different from the pH values measured in the trials SI and S3. The results of the investigation suggested that wheat straw had a high capacity for binding of ammonium. Consequently, nitrification process could not be expected. With spruce sawdust, a slight but significant inhibition of urea hydrolysis and of the nitrification process was observed.