Nitrate leaching risk is increased under exercise grazing in organic farming

There is a trend in organic dairy farming towards higher milk yields associated with more concentrates and less grazing. Grazing is usually compulsory but grass intake from grazing varies greatly. This has consequences for nitrogen (N) transfer from stable to field and for the risk of N leaching. Our aim was to compare different management options for grazing in moderate to intensive organic farming. In a 2-year study, five differently managed fields on three farms in northwest Germany were compared. We analysed parameters of milk production and grassland management, calculated N balances and quantified residual soil mineral N (SMN) as an indicator for N leaching. Residual SMN (0-90 cm) varied on average from 33 to 84 kg N ha(-1)in grazed areas and from 71 to 180 kg N ha(-1)in functional areas like watering places. Soil mineral N increased with higher stocking rate, more grazing days and higher N surpluses. Consequently, SMN was higher in pastures used for exercise grazing or night grazing and around watering places. We conclude that intensifying organic dairy farming when associated with a massive N transfer from stable to field, little fodder uptake on pasture, and higher stocking rates increases N leaching risk.