EFFECTS OF UREASE AND NITRIFICATION INHIBITORS APPLICATION ON UREA FATE IN SOIL AND NITRATE ACCUMULATION IN LETTUCE

The effects of amendment of urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and the nitrification inhibitor dicyand iamide (DCD) on urea transformation in soil and nitrate accumulation i n winter lettuce were studied in a cold greenhouse experiment. The DCD inhibited remarkably the nitrification process for more then two mont hs, maintaining significantly higher levels of ammonium in soil soluti on compared to normal urea. The DCD did not decrease the ammonia volat ilization but determined a significant reduction of plant nitrate conc entration at final harvest. The treatment urea + NBPT showed a behavio r slightly different from normal urea with a higher level of soil nitr ate three weeks after nitrogen (N) fertilization. No effects on NO2 pl ant accumulation were observed, but losses of NH3 were significantly r educed.