Effects Of The Inoculum Size Of A Commercial Bacterial Product And The Age Of Sawdust Bedding On Pig Waste Decomposition In A Pig-on-litter System

A 10 week study was carried out in an experimental farm in Hong Kong to examine the effects of the inoculum sizes of a commercial bacterial product imported from Taiwan on in situ composting of pig manure in a pig-on-litter (POL) system. The pig pens using fresh sawdust as bedding material were also compared with those employing aged sawdust (spent sawdust litter). The results show that high microbial populations were recorded in all pig pens. The organic matter released from the pig manure was mineralized and assimilated into microbial biomass. A process similar to mesophilic composting might have taken place. When comparing the pig pen using full dose of bacterial inoculum with that of half dosage, the densities of total aerobic heterotrophs, total fungi, nitrifying and denitrifying bacteria were not different from each other. However, the pig waste mixtures from a half-dosage pig pen had slightly lower contents of organic nitrogen, total protein, total P and total K, but wider C:N ratio. These small differences suggest that it would be possible to reduce the amount of bacterial inoculation to achieve similar "composting" results. In "fresh" and "aged" pens, the microbial population sizes were also similar. However, the waste mixtures collected from pens using fresh sawdust had lower contents of nutrients (including organic and inorganic N, P and K) but wider C:N ratios than the aged pig pen at the start of this investigation. During the 10 week study, total salts and nutrients of the fresh pens increased rapidly, but their C:N ratios dropped dramatically. On the other hand, in aged pens the changes of the nutrient and protein levels in the waste mixture were small. The bedding material of the aged pig pen was more stable and mature, rendering aged sawdust a better bedding material for the POL system.