Effects of Composted and Raw Organic Amendments on N2o Emissions in a Horticultural Cropping System.

Reducing the amount of synthetic fertiliser inputs and promoting the storage of soil organic carbon through the use of organic amendments can be an effective pathway to reduce greenhouse gas (GHG) emissions and improve Nitrogen (N) use efficiency. High temporal resolution GHG sampling (sub-daily), using automated gas chambers, was employed to observe the effect of raw (CM) and composted (CCM) chicken manure in combination with conventional (CONV, 100% of standard N application) or reduced (100% - N_{[org amend]}) nitrogen fertiliser rates on N₂O emissions in an intensive, irrigated vegetable production system on a black Vertosol in sub-tropical Australia. Three consecutive crops (Phaseolus vulgaris L., Brassica oleracea L. var. Italica and Lactuca sativa L.) showed no significant differences in yield and biomass production between treatments at any rate of synthetic fertiliser applied. The highest N₂O emissions were measured in the CM plus reduced fertilizer (Rd) regime (3.5 t ha^-1 of CM plus 252 kg N ha^-1 urea) with a total emissions value of 1748 g N₂O-N ha^-1 yr^-1. CCMRd and zero nitrogen (0N) treatments emitted the lowest amounts of N₂O with 967 and 854 g N₂O-N ha^-1 from 19 t ha^-1 of CCM plus 249 kg N ha^-1 urea and zero N respectively. Application of organic amendments prior to the first crop in the rotation triggered N₂O emissions for both CM treatments and for CCM plus 100% fertiliser treatment. Emissions from CCMRd and CONV during that period were not significantly different to 0N.  In the subsequent crops, the incorporation of crop residues had a significant impact on the annual N₂O budget. The results showed that fertilizer induced emissions were low, and that use of raw organic amendments increases N₂O emissions. The application of composted rather than raw organic amendments integrated with nitrogen fertiliser can be an effective pathway to reduce GHG emissions and improve N use efficiency.