Abstract
A new in situ method was proposed for investigating chemical and biochemical reactions at micro-sites in the submerged soil. The method as applied to denitrification study was described in detail. Four kinds of solution could be injected into the desired small region of the submerged soil through a tube with a needle at its tip. The soil solution in this region was collected by a tube with a porous cap and analyzed for N_2O by a gas chromatograph. The 4 solutions were (1) distilled water (activity of natural N_2O formation), (2) C_2H_2-dissolved water (total activity of natural denitrification), (3) C_2H_2-dissolved water containing NO_3 (activity of denitrification which was not limited by NO_3 content), and (4) C_2H_2-dissolved water containing both NO_3 and organic compound (activity of denitrification which was not limited by contents of NO_3 and organic substrate). If these 4 kinds of solutions were injected successively, 4 different denitrifying activities could be measured for the desired small region in the submerged soil. Two preliminary experiments were carried out to demonstrate usefulness of the new method. The one was to clarify the relation between soil Eh and ratio of N_2O/N_2+N_2O in denitrification product. The other was to test which organic compound was effective as a substrate for denitrification. In the second experiment, it was found that alanine, histidine, sodium tartrate, etc., were favourable and sucrose, raffinose, sodium citrate, etc., were not favourable for denitrification.
