Effects of commercial bacterial products on nutrient transformations of pig manure in a pig-on-litter system

A preliminary study was carried out in an experimental farm in Hong Kong to investigate the changes in microbial populations and nutrient concentrations of a pig waste mixture during a 10-week in-situ decomposition of pig manure in a pig-on-litter system. The effects of two commercially available bacterial products on this decomposition process were also examined. The results show that both heterotrophs and nitrifiers increased their populations to 10¹⁵ MPN (Most Probable Number) g⁻¹ waste mixture at the end of the 10-week study while the denitrifiers varied around 10¹⁰ MPN g⁻¹ during the period of investigation. By contrast, the fungal Colony Forming Units (CFU) declined rapidly within the first week and remained at 105 CFU g⁻¹ waste mixture throughout the rest of the study period. There was no accumulation of inorganic N in the pig waste mixture. The offensive odour of NH, was not detected in the pig pens. The C:N ratios of the waste mixture gradually declined reaching a final value of 22:1. The concentration of total Kjeldahl N, phosphorus and potassium in the final product were significantly higher when compared with the initial phase of the study. These findings suggest that a part of the organic nutrients released from the pig manure might have been mineralized and assimilated into microbial biomass similar to compost. In general, the nutrient concentrations of the two pig waste mixtures treated by two different bacterial products were similar. This indicates that the effects of these two products on the in-situ decomposition of pig manure were fairly similar. A control pen without the addition of bacterial products became foul within one week and had to be abandoned.