Changes in chemical properties during composting of spent pig litter at different moisture contents

Abstract

An ordinary pig pen employing the pig-on-litter system was set-up and 40 pigs were placed inside. After 12 weeks, the pigs were removed from the pen and the spent litter was collected and piled up in an open shed for further composting and maturation. Three piles of the spent litter were set up with moisture content adjusted to 50% (Pile A), 60% (Pile B) and 70% (Pile C). During further composting, the changes in temperature and chemical properties of the piles were monitored. Results of the study revealed that moisture content affected the changes in temperature and chemical properties (i.e., concentrations of NH+/4-N, [NO-3 + NO-/2]-N, C:N ratio, cation-exchange capacity [CEC], total and water extractable K and pH value) of the spent litter. Pile C, the pile adjusted to 70% moisture, had a delay in reaching peak temperature values and the temperature never dropped back to the ambient level. Piles A and B, the piles adjusted to 50 and 60% moisture content respectively, had very similar changes in temperature and chemical properties and had faster decomposition rates than pile C suggesting that moisture content between 50 and 60% is the suitable moisture content for an efficient further composting of spent litter. The maturation of spent litter was accompanied by changes, with periods of composting in pH, total C, ash, various forms of N, CEC and C:N ratio. Results of the regression analysis showed a curvilinear relationship between these chemical parameters with period of composting and temperature. Moreover, changes in these chemical parameters were found to be either positively or negatively correlated with temperature.