Nitrate leaching from organic farms and conventional farms following best practice

Abstract

Abstract. This paper compares nitrate leaching losses from organic farms, which depended on legumes for their nitrogen inputs (66 site years) with those from conventional farms using fertilizers under similar cropping and climatic conditions (188 site years). The conventional farms were within Nitrate Sensitive Areas in England, but sites following special practices associated with that scheme were excluded. Nitrate losses during the organic ley phase (including the winter of ploughing out) were similar (45 kg N ha –1 ) to those from conventional long‐term grass receiving fertilizer N inputs of less than 200 kg N ha –1 (44 kg N ha –1 ) and from the grass phase of conventional ley‐arable rotations (50 kg N ha –1 ). Losses from conventional grass receiving higher N inputs were greater than from organic or less intensive grass. Nitrate losses following arable crops averaged 47 and 58 kg N ha –1 for the organic and conventional systems respectively, with part of the difference being due to the greater proportion of non‐cereal break crops in the latter. Thus under similar cropping, losses from organic systems are similar to or slightly smaller than those from conventional farms following best practice.