Ammonia volatilization of soil after doses of urea with urease and nitrification inhibitors in pineapple culture

ABSTRACT

The urease inhibitor N-(n-butyl) thiophosphorictriamide (NBPT) and nitrification inhibitor dicyandiamide (DCD) can minimize nitrogen (N) losses by ammonia (NH₃) volatilization, decreasing the speed of urea hydrolysis and ammonium to nitrate conversion, respectively. The objective of this study was to evaluate the soil N losses by volatilization after the addition of N doses in the form of urea combined with urease and nitrification inhibitors in the Minas Gerais semiarid. A randomized complete block design was used with three replications and a 4 × 5 × 7 factorial scheme - four combinations of urea inhibitors (common urea, urea + NBPT; urea + DCD; and urea + NBPT + DCD), five N levels (0.0; 3.7; 7.4; 11.1; and 14.8 g/plant), and seven evaluation times (3, 6, 9, 12, 15, 18, and 21 days) - after topdressing in irrigated pineapple crop. The losses of ammonia and pH around the urea granule were evaluated. The urease inhibitor (urea + NBPT) was more efficient in the lower N levels; in addition, it decreased and delayed the periods of N-NH₃ volatilization and also decreased the pH of the soil, probably due to the higher nitrification and/or increase of the decomposition rate of soil organic matter by the greater availability of N compared with the urea and urea + DCD treatments. The relative N losses were reduced with the increase of N levels, because of the greater saturation of the enzyme urease action sites.

Keywords:
nitrogen; stabilized fertilizers; NBPT; DCD