Resumo

BRITO, L. M.; MOURAO, I.; TRINDADE, H.  e  COUTINHO, J.. Production of mineral nitrogen during composting of dairy cattle slurry solid fraction. Rev. de Ciências Agrárias [online]. 2009, vol.32, n.1, pp.323-334. ISSN 0871-018X.

Screw pressed dairy cattle slurry solid fraction (CSSF) was collected during 2004 and 2005 from two dairy farms with 30% and 22% -24% dry matter (DM) content and the effects of covered either with black polyethylene or with polypropylene, pile dimension, straw addition and of turning frequency on the fate of N were examined. The CSSF with 30% DM was collected at a rate of 1 m³ h^-1 and the material with 22% 24% DM was collected at the rate of 4 and 3 3 _h-1 min 2004 and 2005, respectively. Thermophilic temperatures were attained soon after separation of CSSF with 30% DM. In contrast, temperatures were much cooler in CSSF with 22% DM without straw. The pH ranged from 8 to 9 and C/N ratio was similar amongst treatments on each sampling occasion. Mineral N production was characterized - by high NH4⁺ and low NO3 contents during the thermophilic phase followed by a decrease of NH4⁺ and an increase of NO3 towards the end of composting. Higher DM, and straw addition were both associated with lower NH4⁺ compost concentrations. Therefore, to minimize the N loss as NH3 gas caused by the alkaline pH during the thermophilic phase of composting, it is suggested: i) to increase DM by slowing the rate of the screw dewatering mechanism; ii) to increase the C/N ratio of composting mixture; and iii) to reduce turning frequency.

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