The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 278

S. Fortuneet al. N, P and K Budgets for Some UK Organic Farming Systems

4.8

N, P and K Budgets for Some
UK Organic Farming Systems -
Implications for Sustainability

S. F ORTUNE 1 , J.S. C ONWAY 2 , L. P HILIPPS 3 ,
J.S. R OBINSON 4 , E.A. S TOCKDALE 1

AND C.A. W ATSON 5

1
Soil Science Department,IACR-Rothamsted,Harpenden,
HertfordshireAL5 2JQ; 2 The Royal Agricultural College,
Cirencester, Gloucestershire GL7 6JS; 3 Elm Farm Research
Centre,HamsteadMarshall, Newbury, Berkshire RG20 0HR;
4
Soil Science Department, University of Reading,Whiteknights,
PO Box 233, Reading RG6 6GW; and 5 Environment Division,
Scottish Agricultural College,Craibstone,Bucksburn, Aberdeen
AB21 9YA, UK

Introduction

The economic and environmental sustainability of organic farming is
dependent on the efficient use of nitrogen (N), phosphorus (P) and
potassium (K). Organic farmers aim to maintain and increase the long-term
fertility of soils while minimizing nutrient losses (International Federation
of Organic Agriculture Movements (IFOAM)). The emphasis of organic
farming is to encourage the efficient cycling of nutrients rather than rely on
fertilizers and purchased manure (Lampkin, 1990). On many conventional
farms, large inputs of fertilizers and animal feeds, at levels above those
removed in outputs, have led to an accumulation of nutrients, such as P,
to a degree that many soils have been classified as over-fertilized (Sharpley
and Smith, 1989; Mäder et al ., 1999). N is brought into organic farming
systems through the inclusion of N-fixing crops in the rotation and, as a
result, N balances for organic farms are usually positive (Nguyen et al .,
1995). The potential for large losses of N when leguminous leys are
ploughed led the Royal Commission on Environmental Pollution (1996) to
conclude that 'organic systems are inherently liable to nitrogen leaching'.
The often reduced inputs of P and K to organic farming systems are
believed to lead to negative P and K balances. Johnston (1991) suggested
that organic systems are not inherently more sustainable than conventional
farming, especially with regard to the long-term availability of P and K.