Ammonia Loss and Associated Reactions of Urea in Calcareous Soils

Abstract

Urea in soil is a mobile compound which can be lost by leaching or ammonia (NH3) volatilization. This research examined the contributions of water additions and chemical reactions in explaining the behavior of applied urea.Urea [CO(NH2)2] initially moves undissociated into the soil with added water. Ammonia losses from surface‐applied urea thus decreased with increasing amounts of applied water. Ammonia losses from urea were minimal if injected into the soil 2.5 cm or more, whereas NH3 losses from (NH4)2SO4 (AS) were still high when placed 7.5‐cm deep. Application of AS produced chemically equivalent amounts of Ca and Mg whereas urea and NH4OH precipitated Ca and Mg. The amount of Ca and Mg precipitated increased with decreasing NH3 losses. Precipitation of divalent cations enhanced adsorption of NH4 on soil cation exchange sites, thereby reducing upward movement of NH4 and subsequent NH3 losses. The presence of Ca from reaction of AS with CaCO3 enhanced upward movement of NH4 and increased NH3 losses.

Nitrogen Management in Calcareous Soils: Problems and Solutions

“…Dissolution of ammonium containing fertilizers does not occur when water contents are between 0 to 8%. Maximum losses of NH3 are observed with 8% water content when N was applied as (NH4)2SO4, and 55% water contents show lower ammonia losses as compared to 8% to 30%, while at 0% all of the applied NH4 + -N fertilizer is retained in soil (Fenn and Miyamoto , 1981). Fertilizer placement: Losses of ammonia volatilization are decreased as soon as the fertilizer is incorporated into the soil (Grant, 1996).…”

“…Sources of N fertilizers: Loss of N through volatilization was estimated highest from ammonium containing fertilizers when applied to the calcareous soils (Turner et al, 2012). Fenn and Miyamoto (1981) evaluated that ammonia volatilization losses were lowest from NH4-NO3 and NH4-Cl as compared to ammonium sulphate. Black et al, (19854) reported that NH3 volatilization losses are 5-15% higher when urea is applied compared to other N sources.…”

Balanço do nitrogênio (15N) da uréia nos componentes de uma pastagem de capim-marandu sob recuperação em diferentes épocas de calagem

“…Entretanto, mesmo em solos tropicais ácidos, quando se exaurem os cátions das proximidades do grânulo de uréia para trocar e reter o amônio, ocorre a volatilização, pois, uma vez desencandeado o processo de hidrólise da uréia, há elevação do pH em torno do grânulo de uréia em níveis suficientes para provocar perdas de amônia (Fenn & Miyamoto, 1981;Fenn & Richards, 1986;Tisdale, 1984;Sengik, 1993). Kiehl (1989) exemplificou o efeito alcalinizante decorrente da hidrólise da uréia aplicada em um solo do tipo areia quartzosa (Neossolo Quartzarênico), com pH ácido.…”

Adubação de soqueira de cana-de-açúcarcom soluções de carbonato/bicarbonato de amônio em mistura com sais de potássio e de fósforo

“…2+ e Mg 2+ com o carbonato proveniente da hidrólise da uréia ou carbonato/bicarbonato de amônio, em valores de pH acima de 7, diminuindo o valor máximo de pH atingido e liberando sítios de adsorção para o cátion amônio (Du Plessis & Kroontje, 1966;Fenn & Miyamoto, 1981). Em função do pH exigido para a precipitação dos cátions divalentes, a adsorção do NH 4 + resultante é mais efetiva em solos alcalinos.…”