Net nitrogen mineralization in soils under six indigenous tree species, an abandoned pasture and a secondary forest in the Atlantic lowlands of Costa Rica

Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species, Stryphnodendron microstachyum Poepp. et Endl. (1.1-1.9 mg kg⁻¹ day⁻¹) and Dalbergia tucurensis Donn. Smith (0.7-1.5 mg kg⁻¹ day⁻¹), than under the non-N-fixing trees in the plantation, Vochysia guatemalesis Don. Sm., Vochy sia ferruginea Mart, Dipteryx panamensis (Pittier) Record and Meli and Hyeronima alchorneoides Fr. Allemao (0.2-0.8 mg kg⁻¹ day⁻¹). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.