Effects of a urease inhibitor and aluminium chloride alone or combined with a nitrification inhibitor on gaseous N emissions following soil application of cattle urine

• The effects of NBPT or AlCl3 alone or combined with DMPP on emissions were evaluated.
• DMPP with either NBPT or AlCl3 had the same effect on nitrification as DMPP alone.
• Increasing the concentration of NBPT or AlCl3 did not significantly reduce gaseous N emissions.
• DMPP with either NBPT or AlCl3 increased NH3 emissions and reduced NO and N2O emissions.
• NBPT, with or without DMPP, was more effective at reducing gaseous N emissions than AlCl3.

Addition to soil of separated cattle-urine obtained from housing with urine-faeces segregation systems is an important source of gaseous nitrogen (N) emissions. This study aimed to evaluate the effect of adding different concentrations of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and aluminium chloride (AlCl3), alone or combined with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), on gaseous N losses and N transformations in soil amended with cattle-urine.Using laboratory incubations soil was amended with cattle-urine (200 kg total N ha−1) containing NBPT (0.1 or 1.0%) or AlCl3 (0.5 or 1.0%) either as a single additive or combined with 0.5% DMPP. Three additional treatments were included: soil only (Control), soil amended only with cattle-urine and soil amended with cattle-urine and DMPP.The addition of NBPT at 1% significantly delayed urea hydrolysis during the first 4-d after urine application comparatively to treatments receiving AlCl3. Nitrification was inhibited by addition of DMPP, with no further effect (P > 0.05) when DMPP was combined with NBPT or AlCl3. The AlCl3 treatment had no effect on urea hydrolysis or nitrification. The combination of DMPP with NBPT or AlCl3 increased (P < 0.05) NH3 emissions and reduced (P < 0.05) NO and N2O emissions compared with urine alone. It was concluded that NBPT was more effective at reducing gaseous N emissions from cattle-urine applications than AlCl3, and that NBPT alone was more effective than NBPT combined with DMPP. No advantages were gained from the combination of one of these additives with DMPP on total gaseous N emissions.