It has long been recognized that soil organic matter is the key to soil
fertility. As a nutrient store it gradually provides essential elements
which the soil cannot retain for long in inorganic form. It buffers
growing plants against sudden changes in their chemical environment and
preserves moisture in times of drought. It keeps the soil in a friable,
easily penetrated physical condition, well-aerated and free draining,
providing young seedlings with an excellent medium for growth. But it
has another property, the nature and extent of which have been the
subject of argu- ment and controversy ever since scientists began to
study the soil, and that is its ability to affect growth directly, other
than by providing nutrient elements. Any- one wishing to learn about
these effects has been faced with a daunting mass of literature, some
confusing, often contradictory, and spread through a multitude of
journals. Individual aspects have been covered from time to time in
reviews but there has obviously been a need for a modern authoritative
text book dealing with the many facets of this subject, so the
publication of this volume is timely. The editors and authors are all
specialists in their fields, fully familiar with the com- plex nature of
soil organic matter and with the particular difficulties arising in any
study of its properties. Where controversies exist they have presented
all sides of the argument and have highlighted areas where further work
is badly needed.