Norwegian Journal of Agricultural Sciences : ammonia exchange between crops and air

Abstract

The chemical, biochemical and physiological factors that govern the exchange of NH3 between plants and air are reviewed together with methods for measuring the gas exchange. The NH4• concentration and pH in plant cells differ between organelles. NH4• concentrations in the range of 1-50 mM and apoplast pH in the range of 5.3 - 7.0 have been reported. Physiochemical calculations indicate that such NH4• concentrations enable crops to emit NH3 under most circumstances during daytirne when stomata are open. The amounts emitted depend on interacting environmental and physiological factors. High temperatures enhance emission of NH3. The studies reviewed indicate thai crops are net emitters of NH3 to the atmosphere. Whilst losses are highly variable between crops and seasons it is suggested that for arable crops in temperate regions net losses of NH3 to atmosphere are of the order of 1-2 kg NH3N ha' y-'.