Increased growth of ryegrass exposed to ammonia

Abstract

Fluxes of ammonia (NH3) between the soil/plant system and the atmosphere are components of the nitrogen cycle, but knowledge of them is inadequate1,2. Grassland in the UK annually receives 8.4 ×l05 tonnes of fertilizer nitrogen3 and 5 × 105 tonnes of nitrogen through the excreta of grazing ruminants4. Emissions of NH3 from these sources may be 105 tonnes annually5 and, apart from the loss of a plant nutrient, they may pollute the air. We report here that NH3 has beneficial effects on growth of perennial ryegrass (Lolium perenne L.), apparently through leaf sorption. In air containing NH3 at 16µgm−3, similar to the level above a grazed pasture6, sorption would be 48–224 ng m−2 leaf area s−1, depending on the density of leaves in the canopy. For grass with a leaf area index of 4, this process would add nitrogen at 6–28 g ha−1 h−1. These results support the suggestion7 that some of the flux of NH3 from soil may be sorbed by overlying plants.