Effects of addition of urea on organic matter decomposition in matured compost
2006
Takahashi, M.(Ishikawa-ken. Livestock Research Center, Hodatsushimizu (Japan))
Urea was added to compost that had long matured and contained little easily decomposable organic matter. This study intended to clarify the effects of addition of urea on the subsequent compost maturation process. Three kinds of campost used as test materials were; poultry feces and wood chips; cattle feces and rice hulls; and swine feces, rice hulls and wood chips. The composts were obtained from a manufacturer in Ishikawa Prefecture where production was done at different facilities. Changes in the chemical constituents of the test compost with added urea (about 10g/kg (DM) nitrogen) were monitored during the 24-month maturation process. After three months, urea had decomposed into ammonium and as the temperature increased, it was converted into nitrate-nitrogen. In the poultry manure, the maximum nitrate-nitrogen and nitrite-nitrogen (NOx-N) contents were 8.7 g/kg (DM) for the urea added sample and 1.5 g/kg (DM) for the control. The organic matter decomposition (OMD) of the former after 24 months was 7%, whereas that of the latter was 31%. Interactions for the elapsed time and the effect of addition were significantly different (P0.01). As to the cattle manure, the NOx-N maximum was 4.3g/kg (DM) for the sample with added urea, and 0.6 g/kg (DM) for the control. The OMD of the former after 24 months was 7%, whereas that of the latter was 15%. Interactions for the elapsed time and the effect of addition were significantly different (P0.01). In the swine manure, the NOx-N maximum was 2.5g/kg (DM) for the urea added sample, and 1.0 g/kg (DM) for the control. The OMD of the former was 12%, whereas that of the latter was 15%. Interactions for the elapsed time and the effect of addition were not significantly different. Results indicate that OMD in the compost was suppressed as the NOx-N content increased to more than 3g/kg.
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