The efficiency of two nitrogen fertilizers, ammonium sulphate and urea, labelled with 15N, in two major Central-Amazonian soils (Yellow Latosol - an Oxisol and Red-Yellow Podzolic - an Ultisol), was studied in greenhouse experiments in Nancy, France, 1992. Italian rye-grass (Lolium multiflorum L.) was used as the test plant. Rye-grass nitrogen uptake of ammonium sulphate ranged from 44 to 49%, and of urea from 60 to 70%. Immobilization and losses of nitrogen were dependent on the fertilizer type. Microbial nitrogen immobilization was higher in the presence of urea, while losses were higher with ammonium sulphate. Since losses of nitrogen fertilizers from leaching were practically nil under the experimental conditions, they might have occurred mainly through gaseous form.
15N; nitrogen fertilizer; Oxisol; Ultisol; Central Amazon