Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 149

D.L.J. Hatleyet al. Changing Farming Practices onSOM

3.7

The Impact of Changing
Farming Practices on Soil
Organic Matter and Soil
Structural Stability of Fen Silt
Soils

D.L.J. H ATLEY 1 , T.W.D. G ARWOOD 2

AND

P.A. J OHNSON 1

1
ADAS, 22WillingtonRoad,Kirton, Boston, Lincolnshire PE21 7JU;
and 2 ADAS,Boxworth, Cambridge CB3 8NN, UK

Introduction

Increases or additions of soil organic matter can improve soil properties
in many ways. Better plant nutrition (N, P, S and micronutrients), ease
of cultivation, penetration and seedbed preparation, greater aggregate
stability, reduced bulk density and improved water-holding capacity have
all been observed (Johnston, 1986). This implies that a decrease in organic
matter, e.g. by oxidation following cultivation, will adversely affect most, if
not all of these properties, even if, in the long term, organic matter reaches
an equilibrium with additions of organic matter in crop residues (Arrouays
and Pelisser, 1994).
Evidence from the Representative Soil Sampling Scheme (1969-1985)
suggests that there has been a reduction in the proportion of arable soils
with 'high' (> 8%) and 'low' (< 1.8%) organic matter levels in England and
Wales (Skinner and Todd, 1998), whilst average organic matter levels for
all crops and grass have remained static during the same period.
In the 1960s, 14 sites were selected on the fertile silt-lands of the
Holland district of Lincolnshire to assess changes in soil organic matter
levels, because of concerns that declining soil organic matter levels were
compromising the sustainability of agricultural production on these soils.
Results from 1964 to 1989 were reported by Johnson and Prince (1991).
This chapter presents results from the last sampling in 1996.