Soil Teeming with Life: New Frontiers for Soil Science - Sustainable Management of Soil Organic Matter - page 405

R.M. Reeset al. SustainingSOM

6.1

Sustaining Soil Organic Matter

R.M. R EES 1 , B.C. B ALL 1 , C.D. C AMPBELL 2 AND

C.A. W ATSON 3

1
Environment Division, Scottish Agricultural College, Edinburgh
EH9 3JG; 2 Macaulay Land Use Research Institute,Craigiebuckler,
Aberdeen AB15 2QH; and 3 Environment Division, Scottish
Agricultural College,Craibstone,Bucksburn, Aberdeen
AB21 9YA, UK

Introduction

Concern about the loss of organic matter from soils and the implications of
this for the sustainable functioning of soils is not new, but the increasing
demands that are being placed on our environment are leading to an urgent
need to reassess the role played by soils in the development of sustainable
patterns of land use. This topic has helped to achieve this by providing a
wide-ranging selection of relevant research papers and reviews. In this
chapter we review some highlights from the material presented and outline
what we see as the main conclusions.
The concept of soil quality is used to define those attributes of soils that
are essential to soil functions such as nutrient storage, the provision of a
suitable physical environment for plant growth and the attenuation of
pollutants. In the opening chapter of this topic, this concept was reviewed
by Carter, where he emphasized the importance of defining precisely those
attributes that are pivotal in controlling organic matter quality as well as the
need to develop standardized measurement and sampling procedures.
Carter identified specific fractions of organic matter that describe soil qual-
ity. These include macroorganic matter, microbial biomass and carbohy-
drate contents. Silt- and sand-sized macroorganic matter is important in
maintaining the protection effect of soil organic matter. This acts mainly in
promoting and stabilizing soil aggregation. Loveland et al . proposed that
the important component of soil organic matter is the 'active fraction',
made from recent additions of crop residues and organic manures.
Cultivation and compaction can be associated with physical
degradation. Cultivation generally depletes organic matter and reduces soil