Resolution of the N-15 balance enigma?

The enigma of soil nitrogen balance sheets has been discussed for over 40 y ears. Many reasons have been considered for the incomplete recovery of N-15 applied to soils, including sampling uncertainty, gaseous N losses from pl ants, and entrapment of soil gases. The entrapment of soil gases has been w ell documented for rice paddy and marshy soils but little or no work appear s to have been done to determine entrapment in drained pasture soils. In th is study N-15-labelled nitrate was applied to a soil core in a gas-tight gl ovebox. Water was applied, inducing drainage, which was immediately collect ed. Dinitrogen and N2O were determined in the flux through the soil surface , and in the gases released into the glovebox as a result of irrigation or physical destruction of the core. Other components of the N balance were al so measured, including soil inorganic-N and organic-N. Quantitative recover y of the applied N-15 was achieved when the experiment was terminated 484 h after the N-15-labelled material was applied. Nearly 23% of the N-15 was r ecovered in the glovebox atmosphere as N-2 and N2O due to diffusion from th e base of the soil core, convective flow after irrigation, and destructive soil sampling. This N-15 would normally be unaccounted for using the sampli ng methodology typically employed in N-15 recovery experiments.