Nitrogen leaching losses from mixed organic farming systems in the UK

Food production conforming to organic standards (UKROFS, 1991) relies on supplying plant nutrients through management of biologically regulated processes within a rotation. In the UK, organic farming systems are based primarily on mixed ley-arable crop rotations that allow nutrients to be: recycled within the farm. The ley-arable rotation offers an opportunity to use nitrogen supplied by biological fixation to support animal production and subsequent arable cropping. Within such rotations the relative proportion of ley and arable not only are a fundamental determinant of total N input but also critically affect the character of livestock production and the amount of farmyard manure produced. Although reliance on external inputs is reduced in organic systems, losses of nutrients still occur, primarily following the cultivation of leys for arable production. This paper presents nitrogen leaching data from mixed organic farming systems in the UK and examines whether such systems can meet the requirements of EU directive 80/778 on water quality (European Economic Community, 1980). In the UK, Nitrate Sensitive Areas (NSAs) were designated by the Ministry of Agriculture, Fisheries and Food (MAFF) in a Pilot Scheme in 1990, before the EU Nitrate Directive (MAFF, 1990).