Nitrogen losses from the field: denitrification and leaching in intensive winter cereal production in relation to tillage method of a clay soil

Losses of soil and fertilizer nitrogen by leaching and denitritication from a clay soil in southern England have been measured over four years. Nitrate losses in drainage water from direct‐drilled land averaged 20–30 kg N ha ‘a’ with wide seasonal variation. Ploughing and conventional cultivations increased this loss. Denitritication from direct‐drilled land averaged 5–10 kg N ha ‘a’ with wide seasonal variation. Ploughing and drainage both diminished denitritication losses but cultivation had the greater effect. These nitrogen losses occurred mainly in autumn and spring. Nitrogen losses, in drainage water or by denitritication after spring fertilizer applications, were related to the rainfall in the 28 days following top dressing. Approximately 40 mm rain was needed to cause a loss of 10% of the nitrogen applied but in practice losses were quite variable.