Sutton MA, Milford C, Nemitz E, Theobald MR, D. F, Schjoerring JK, Mattsson ME, Nielsen KH, Husted S, Erisman JW, et al. Biosphere-atmosphere interactions of ammonia with grasslands: experimental strategy and results from a new European initiative. Plant and Soil . 2001 ;228 (1):131-145.