SIMULTANEOUS DETERMINATION OF NITROGEN TRANSFORMATION RATES IN SOIL COLUMNS USING 15-N - N-MODEL OF A TERRA FUSCA-RENDZINA SOIL

Rates of ammonification, nitrification, immobilization, and denitrification were determined in undisturbed columns of a Terra fusca Rendzina soil. A steady input of 15-N labelled ammoniumsulfate with the irrigation water created a steady state of the turnover processes in the soil resulting in a constant output of 15-N-nitrate. In this state the rate constants (8-degrees-C) were K1 = 0.64 for the netto-N-nitrification, K2 = 0.11 for the netto-N-denitrification, and K3 = 0.25 for the netto-N-immobilization. 64% of the nitrate was leached, 25% immobilized in organic matter, and 11% denitrified. Relating these rate constants to the turnover of the soil nitrogen one can calculate the mean annual rates for the different processes of a forest soil, using the mean annual temperature. For the Gottinger Wald situation (T = 6.9-degrees-C) the following rates were calculated; Ammonification = 183 kg N.ha-1.a-1, immobilization = 44 kg N.ha-1.a-1, netto N-denitrification = 19 kg N.ha-1.a-1, and netto-N-mineralization = 120 kg N.ha-1.a-1.