Studies on the humus forms of forest soils

Brown forest soil samples previously employed (1, 2) were incubated for 20 weeks and analyzed for the patterns of nitrogen transformation when 10 mg of nitrogen per 100 g of dry matter as ammonium sulfate were added. The result obtained are summarized as follows. 1) In the case of L layer samples, the addition of nitrogen restrained ammonification but accelerated the immobilization of nitrogen, while in the later periods ammonification was ac.celerated. 2) In the F-H-A layers, the effect of the treatment differed among different soil types. In samples from the dry type soil, the acceleration of ammonification in the middle stages of incubation was the most significant effect caused by the treatment, and in the samples from the wet type soil, the acceleration of nitrification and restraint of ammonification from early stages to the middle was the most important effect. 3) The addition of nitrogen to the samples from the A-A-B horizons caused the acceleration of nitrification and restraint of ammonification for samples of the wet type soil, but there was no significant effect in the case of dry type soil samples. 4) The repetitions of rise and fall of the levels for total inorganic nitrogen, NH4-N and NO3-N observed for the non-treated samples were reversed with the addition of nitrogen.