Abstract

CARNEIRO, J.P.; BRANCO, S.; COUTINHO, J.  and  TRINDADE, H.. Nitrogen mineralization from different organic residues in long-term laboratory incubation. Rev. de Ciências Agrárias [online]. 2007, vol.30, n.2, pp.159-173. ISSN 0871-018X.

The aim of this study was to evaluate, through a long-term incubation experiment (443 days) conducted under laboratory conditions, the N net mineralization progress after addition to soil of different amendments: sewage sludge, cattle slurry, municipal solid compost and pulp mill sludge. Excluding pulp mill sludge, the residues were applied at two rates (80 and 160 kg total N ha^-1). Treatments with the same rates of mineral N fertilizer and a control were also included. N net mineralization was evaluated using the mineral N content (NH4⁺-N and NO3^--N) accumulated in the mixtures of soil+residue. Measurements were performed at 1, 2, 3, 4, 8, 11, 15, 22, 29, 36, 46, 59, 74, 88, 120, 144, 186, 249, 338 and 443 days after residues application. Highest values of soil mineral content at the beginning of the experiment were obtained on the treatments with cattle slurry and sewage sludge amendments. After 443 days of incubation, the treatments with cattle slurry and sewage sludge released respectively, 50 and 76% of the total N applied (two rates mean). Pulp mill sludge and municipal solid compost treatments originated N immobilization, with this effect lasting for a period of 4-5 months and one month respectively. After 443 days of incubation, the treatment with pulp mill sludge showed an immobilization of 43%, relatively to the amount of total N added. And the treatment with municipal solid compost showed a mineralization of 26% of the total N added. The organic amendments showed a very diverse N mineralization behaviour, which may imply distinct practical results. Application of cattle slurry and sewage sludge should be accompanied by reduction of the amounts of mineral fertilizer applied in a short-term period, while the addition of municipal solid compost and, mainly, the addition of pulp mill sludge may need a reinforcement of the rate of the mineral N fertilizers applied.

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