Nitrous oxide and carbon dioxide emissions during initial decomposition of animal by-products applied as fertilisers to soils

The recycling of organic wastes as soil amendments is notably promoted in sustainable agricultural systems. However, for many animal by-products approved by organic farming regulations little is known about their effects on the greenhouse gas balance of the soil, in particular on N(2)O emissions. In this work we report on the N(2)O and CO(2) emissions from six animal-derived wastes (horn and hoof meal, blood meal, hydrolysed leather, meat bone meal, chicken manure and a commercial organic mixed fertiliser). We compared these emissions to those from a mineral fertiliser (calcium ammonium nitrate) in a sandy and a loam soil during a three month laboratory incubation study. N(2)O flux dynamics varied strongly with residue category and soil type. In the sandy soil, cumulative N(2)O emissions correlated with soil NO(3)(-) content. Although the mineral fertiliser produced the highest total N(2)O emissions (5.7 mg N(2)O-N kg(-1) soil), the commercial organic fertiliser mixture led to statistically similar emissions (5.3 mg N(2)O-N kg(-1) soil). The other by-products emitted between 1.3-3.0 mg N(2)O-N kg(-1) soil, and only blood meal emitted less than 1 mg N(2)O-N kg(-1) soil. In the loam soil. N(2)O emissions never exceeded 1.0 mg N(2)O-N kg(-1) soil, and did not correlate with NO(3)(-) in soil. With regard to CO(2) emissions and C storage potential, chicken manure was the only residue that significantly accumulated C in both soils during the course of our experiment. The addition of an extra easily available source of C (glucose) or N (NO(3)(-)) influenced N(2)O emissions differently depending on the residue applied. Our results showed that despite the extra amount of C added with the organic amendments, N(2)O emissions from animal-derived wastes were never higher than those from the mineral fertiliser. (C) 2010 Elsevier B.V. All rights reserved.