Abstract: With a simulated brown soil column experiment under constant temperature and humidity, using single application of urea as the control, this paper studied the effects of different treatments, including reduced-amount urea, reduced-amount urea combined with corn stalk, reduced-amount urea combined with NBPT urease inhibitor and DMPP nitrification inhibitor, and reducedamount urea combined with corn stalk and inhibitor, on ammonia volatilization characteristics. The correlation of NH₄⁺-N, NO₃^--N, pH and the ammonia volatilization rate was analyzed. The results showed that the ammonia volatilization rate was effectively restrained by different reducedamount urea combined application treatments, with a peak appearing 2-8 days later than the single application of urea. Under the treatment of reducedamount urea combined with corn stalk and inhibitor, the ammonia volatilization rate peak value and the accumulation loss during 18 days of incubation decreased by 74.27% and 43.96%, respectively. The ammonia volatilization rate had a positive correlation with NH₄⁺-N concentration and pH value, and had a negative correlation with NO₃^--N concentration. The treatment of reducedamount urea combined with corn stalk and inhibitor could maintain a high level of NH₄⁺-N (>350 mg·kg^-1) for a long time after peak appearing, and could also effectively reduce the NO₃^--N accumulation in soil.

Key words: paddy soil, upland, the Second National Soil Survey, spatial variation, soil acidification