EVOLUTION OF DINITROGEN AND NITROUS OXIDE FROM NITROGEN-15 FERTILIZED SOIL CORES SUBJECTED TO WETTING AND DRYING CYCLES.

A laboratory study was conducted to establish trends in evolution of dinitrogen (N//2) and nitrous oxide (N//2O) associated with the wetting and drying of soils and to assess the relative significance of nitrification and denitrification as sources of the N//2O evolved from NH//4** plus //-fertilized soils. Mass spectrometric procedures were used to analyze atmospheric samples collected each day during a 6-week period from intact soil cores treated with **1**5N-labeled KNO//3 (65. 6 atom % **1 5N) or (NH//4)//2SO//4 (81. 4 atom % **1**5N) at a rate equivalent to 100 kg N hA** minus **1 and periodically treated with water to simulate rainfall. Data reported show that N//2 and N//2O were evolved only if enough water was applied to increase the soil moisture content to a level above the 0. 03-MPa moisture percentage, that these gases were evolved concurrently, that maximal evolution occurred 2 to 9 D after the water had been applied, and that more N//2 was usually evolved than N//2O.