Studies on the humus forms of forest soils

Abstract

The non-dried samples from each layer and horizon of the 29 brown forest soils which were analyzed for elementary composition in the previous paper (5), were examined for nitrogen minerallzation by the determination of inorganic nitrogen before and after 20 weeks' incubation. The findings obtained about the inorganic nitrogen contents of the samples after 20 weeks' incubation are summarized as follows. 1) The higher the NT (total nitrogen) level of the sample was, the greater was the amount of N₁ (total inorganic nitrogen) contained in it. 2) In general, both the Nt level and the nitrogen minerallzation rates (N_I/N_T × 1(0) showed a tendency to increase with movement downward from the L layer to the F-H layer, and thereafter there was decrease with increasing depth. 3) The N₁ contained in the L-H-A layers was between 4.7 to 331 mg with one exception (924 mg), and most of it existed as NH₄-N in the majority of the samples except that remarkably large amounts of NO₃-N were found in the F-H-A layers of some wet type soils which had Cryptomeria japonica or broad-leaf tree vegetation. 4) The A-A-B horizons of the wet type soils were distinguished from those of the dry type soils by their higher Nllevels and higher values of the NO₃-N/N_I ratio. 5) The rate of NO₂-N to N_I (NO₃-N/N_I × 100) was found to be generally higher in the A-A-B horizons than in the L-H-A layers with some exceptions.