The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 286

L.Philipps All-arable Organic Rotations

4.9

The Effects of All-arable
Organic Rotations on Soil
Organic Matter Levels and the
Phosphorus and Potassium
Status Over the Period
1987-1998

L. P HILIPPS

Elm Farm Research Centre,HamsteadMarshall, Newbury,
Berkshire RG20 0HR, UK

Introduction

With the growth of the organic sector in Europe, it is inevitable that there
will be an increasing number of conventional specialist arable farmers
considering conversion to organic methods of production. Von Fragstein
(1996) found that the proportion of stockless farms in Germany varied
between 20 and 50%. Similarly, David et al . (1996) and Stopes et al .
(1996a) reported that the stockless system is becoming increasingly
important in organic farming systems in France and the UK, respectively. It
is stated in organic farming principles that organic farming systems should
sustain or build soil fertility. In temperate climates such as in Northern
Europe, mixed ley-arable rotations are the primary means of maintaining
soil fertility, as well as controlling weeds, pests and diseases in organic
crop production systems (Lampkin, 1990). On a mixed organic farm, the
grass-clover ley is expected to accumulate sufficient N by fixation to
support subsequent arable crops. Grass-clover leys typically occupy at least
50% of the mixed farm (National Rivers Authority, 1992), and the manure
generated by the livestock can be used to stimulate biological activity and
move nutrients both around the farm and within the rotation.
However, for economic viability, all-arable or stockless rotations can-
not include a long ley phase to provide a balance between fertility building
and exploitative arable crops. Instead, short-term leguminous green
manures must be used to accumulate N for the subsequent arable phases of
the rotation. Trials on the duration, species composition and management