Effects of swine manure fertilization on autotrophic ammonia oxidizing bacteria in soil.

Molecular and biochemical investigation methods have been exploited to evaluate the effects of pig slurry, used for three years as a fertilizer in intensive agriculture, on the presence and activity of chemolithotrophic ammonia oxidizing bacteria, the biocatalysts of the first step in the nitrification process. The evaluation was carried out, on bulk soil, comparing data from the first and the third year of fertilization. Oligonucleotide sequences selected from the 16S rRNA genes of autotrophic ammonia oxidizers have been used as specific PCR amplification primers and probes. The potential nitrification activity (PNA) has been used to determine the effects of swine manure fertilization on the ammonia oxidizing activity. Members of the genera Nitrosomonas and Nitrosospira were always detectable, but the genus Nitrosospira was more represented than Nitrosomonas. The differences between the hybridization signals were correlated with the doses of pig slurry and the number of applications. The mineral (urea) and organic fertilizations showed similar effects on the ammonia oxidisers investigated by molecular and biochemical methods. It was found that additions of swine manure to soil plots increased both potential ammonia-oxidise activity and ammonia oxidiser sequences. Stimulation of the soil ammonia-oxidise activity was due mainly to its effects on the indigenous bacterial population.