ORGANIC NITROGEN MINERALIZATION IN TEMPERATE HUMID-ZONE SOILS AFTER 2AND 6 WEEKS OF AEROBIC INCUBATION

The N mineralization rate in 11 soils was studied by aerobic incubatio n at 28 degrees C and at a moisture content of 75% of field capacity f or 2 weeks (short term) and 6 weeks (medium term). Relationships betwe en the N mineralization indices for each period were evaluated. Ammoni fication largely predominated during the first 2 weeks of incubation, whereas nitrification was the predominant process between weeks 2 and 6. The net N mineralized in the different soils varied from 0 to 2.85% of the organic N after 2 weeks of incubation and from 0.32 to 3.36% o f the organic N after 6 weeks of incubation, the mean values for each period being 0.82 and 1.51% of the organic N, respectively. The quanti ties of NH4+-N, NO3--N, and total inorganic N produced and the percent age of organic N mineralized after 2 weeks of incubation were highly a nd positively correlated with the corresponding values after 6 weeks o f incubation. These results showed that either length of incubation co uld be used to determine the potential N mineralization capacity of th e soils. Information obtained from the two incubation periods was larg ely supplementary for the kinetic study of N mineralization, ammonific ation, and nitrification; therefore a medium-term incubation with inte rmediate measurements of N mineralization over a short term may be mor e useful than a single measurement using either of the two incubation periods.