Effect of successive rotations of eucalyptus on nitrogen and carbon mineralization of the soil and nitrogen supply in the Southwest of Bahia, Brazil

The aim of this study was to evaluate the effect of successive rotations of eucalyptus cultivation on: (a) organic reserves of nitrogen and carbon potentially mineralizable of the soil and (b) the nitrogensupply from these reserves in Eucalyptus urophylla plantations without nitrogen fertilization. The studywas conducted in commercial plantations of Eucalyptus urophylla on the first, second and third rotation, with reference to Submontane Deciduous Seasonal Forest area. Four experimental units of 400 m(2) were allocated in each area, where samples of deformed and undisturbed soil samples were collected, accumulated litter and tree biomass. From the nitrogen and carbon mineralized amounts during 24 weeks of incubation, the N and C mineralization potential of the soils was estimated. In addition, total soil N, litter and tree biomass levels were determined. To estimate the share of organic reserves in the N supply for eucalyptus plantations, two prediction models were adopted. Soils under eucalyptus by different rotations and native forest have been similar mineralization capacity of N and C, with average mineralization potentials of 47.6 and 597.2 mg kg(-1) of soil, respectively. The nitrogen and carbon mineralization potential of the soil were not altered by eucalyptus cultivation in up to three consecutive rotations. The nitrogen organics reserves of the soil, according to the prediction models, are sufficient to provide the demand of N by eucalyptus between three to eight rotations.