Interactive effects of composts and liquid pig manure with added nitrate on soil carbon dioxide and nitrous oxide emissions from soil under aerobic and anaerobic conditions

The composting process results in immobilization of inorganic N. When high-Ndemanding crops are grown in compost- amended soils, additional N fertilizer is often applied. The combination of elevated nitrate levels from N fertilizer and high C inputs from the compost may result in enhanced greenhouse gas emissions. Hence, the objective of this laboratory incubation study was to characterize CO2 and N2O emissions from a Brookston clay loam soil that has received organic amendments in the presence or absence of added nitrate. The organic amendments included urban yard waste compost (YWC), liquid pig manure + wheat straw compost (PMC), and liquid pig manure (LPM). The nitrate treatments included added nitrate (100 mg KNO3-N kg soil^-1) or no added nitrate. Total CO2 emissions during aerobic incubation followed the pattern: YWC > LPM > PMC > control (no organic amendments) for both nitrate treatments. Nitrate addition increased CO2 emissions from the YWC- and LPM-amended soils by 9 and 43%, respectively, but had no significant effect (P < 0.05) on CO2 emissions from the control or the PMC-amended soil. All organic amendments increased N2O emissions compared to the control. When nitrate was added to aerobically incubated LPM-amended soils, N2O emissions were increased over seven times; however, N2O emissions were decreased by 93% for PMC-amended soils and by 50% for YWC-amended soils. These decreases in N2O production occurred when nitrate was added to the YWC and PMC treatments under aerobic conditions but not under anaerobic conditions. Composted liquid pig manure was found to be more environmentally friendly than raw liquid pig manure as it stabilized the manure C and reduced CO2 and N2O emissions compared to the liquid pig manure.