Action of glyphosate ammonium (GPA) on the nitrification potential of soiltreated with two different slow-release N-fertilizers.

The purpose of this work was to determine the effect on the soil nitrificat ion potential of Glyphosate Ammonium (GPA) and two oxamide N-fertilizer and changes in microbial activity following the possibility of using N-fertili zers more efficiently. Samples incubated at 15 degrees C and 27 degrees C were taken every 15 days during 120 days to determine NO3- production from soils fertilized with an d without GPA. Generally, the addition of GPA did not significantly affect soil enzyme act ivities. The highest nitrification, in fact, was from the 90(th) to the 105 (th) day for all the fertilizers; the oxamidic tertiary complex 15.24.12 re sulted in a more efficient nitrification than conventional fertilizers (ure a and ammonium sulphate), while the microbial activity of the soil, under e quivalent rates of N-addition, resulted in this order: at 15 degrees C: 15.24.12 > Urea = (NH4)(2)SO4 28.14 > Control at 27 degrees C: 15.24.12 > 28.14 = (NH4)(2)SO4 = Urea > Control The gradual hydrolysis of oxamide in 15.24.12 led to NH,I fixation by organ ic colloids in the soil, suggesting that exchangeable NH4+ is released when soluble NH4+ ions are depleted by nitrification or plant uptake.