GREENHOUSE GAS EMISSIONS DURING SWINE MANURE COMPOSTING IN A RECTANGULAR BED WITH DAILY TURNING

Composting is an effective management practice for converting animal waste to a valuable soil amendment that has the potential to reduce pollution. Rectangular bed composting with daily turning is widely used in China, but gas emission from this method has not be reported. The goals of this study were to evaluate seasonal differences in greenhouse gas (GHG) emissions and the relative contributions of the GHGs from a commercial swine manure composting facility with daily turning. The compost mixture of swine manure and mushroom residues was turned and moved forward 2 m every day, and it took approximately 20 d to move the raw materials from the head side to the end side of the composting bed. The gases were sampled daily with the static chamber method, and gas concentrations were measured with a gas chromatograph. Compost and air temperatures were monitored. The compost was sampled every 3 d for nitrogen and carbon contents. Cumulative emissions in spring, summer, autumn, and winter were 14.1 +/- 4.0, 24.1 +/- 2.2, 10.5 +/- 0.8, and 11.9 +/- 3.4 kg CO2 m(-2), respectively; 311 +/- 106, 482 +/- 44, 113 +/- 9, and 105 +/- 21 g CH4 m(-2), respectively; and 2.1 +/- 0.3, 2.7 +/- 0.4, 0.5 +/- 0.2, and 1.3 +/- 0.4 g N2O m(-2), respectively. Averaged over the four seasons, greenhouse gas flux was 12.38 +/- 8.90 g CH4 m(-2) d(-1) and 0.083 +/- 0.048 g N2O m(-2) d(-1). The reason for the lowest emission in autumn was unclear. Excluding CO2, methane contributed approximately 87.5% to 94.9% of the CO(2)e emissions, whereas N2O contributed the rest. Because the static chamber did not capture emissions during turning, it is recommended that more robust methods (such as dynamic plume or mega dynamic chamber) should be applied to measure the emissions for inventory studies. The high temperatures in the last few days indicated that composting was still ongoing and the duration should be increased.