A novel indicator of environmental risks due to nitrogen management on grasslands

An agro-ecological indicator IN losses was introduced in order to estimate the risks of air and water pollution through nitrogen management on grasslands. The IN losses score in this study corresponded to the lowest score of four sub-indicators (INH3, IN2O, INO and INO3) which, respectively, provide information on volatilisation, nitrous and nitric oxide emissions in the air and nitrate leaching in groundwater. The score of each sub-indicator was obtained by comparing nitrogen losses to a threshold which corresponded to the maximal level acceptable for the environment (e.g. 50 mg NO3 L−1 for the leaching sub-indicator INO3). The losses in air of NH3, N2O, NO were calculated by means of emission coefficients. Nitrate leaching was estimated from the residual mineral nitrogen in grassland soil found at the beginning of the drainage period. A validation of the indicator by comparing calculated data with measurements of nitrate leaching by ceramic cups was carried out on grazed and hay grasslands. A discrepancy between observed and calculated data was observed when using data from ceramic cups to validate the indicator. Nevertheless, the indicator gave realistic results and is valid for use in order to indicate the degree of pollution risk in agricultural management.