Nitrous oxide production from urea granules of different sizes

Three laboratory experiments were conducted to determine if urea granule si ze or a high concentration of urea prills influence N2O production in soil. Urea hydrolysis results in a localized increase in soil pH and an increase in ammonia concentration. Such conditions may adversely affect the nitrifi cation process, thereby increasing the N2O to NO3- product ratio. Also, if anaerobic conditions should occur, the N2O to N-2 product ratio during deni trification may increase. In general, under aerobic conditions, increasing the urea granule size from a powder to prill (commercial granules) and to l arger granules resulted in increased N2O production. The increase in N2O pr oduction as granule size increased was accompanied by an increase in NO2- c oncentration. The accumulation of NOS and the lower rates of disappearance of NH4+, or appearance of NO3-, indicated that the nitrification process wa s adversely affected. The appearance of N2O was delayed with increasing gra nule size. A high concentration of urea prills produced a similar but great er effect than large granules. The appearance and rapid production of N2O w as closely related to the rapid disappearance of hydroxylamine and the pres ence of NO2-. The failure to detect hydroxylamine in urea granule-treated s oil may have been due to its rapid oxidation to N2O. The proportion of the added urea N transformed to N2O increased with granule size but did not exc eed 1.24% of the urea added. A high concentration of urea prills resulted i n 2.80% converted to N2O-N.