Issues for More Sustainable Soil System Management 361In the years 1840 to 1842, I proposed that the natural sources which deliver to plants
the nitrogen they need are not sufficient for the [production] objectives of agriculture.
A series of observations as well as continuous reconsideration have indicated to me,
however, that this view is not correct ...
For millennia, millions of people have believed, and millions believe it still,
that the sun revolves around the earth because this is what they perceive. In the
same way, many thousands of farmers have believed, and thousands still believe,
that the practice of agriculture revolves around nitrogen, even though this belief has
never been scientifically validated, and never will be scientifically supported because
all progress and indeed all improvements in agriculture revolve around the soil
(republished in Liebig, 1995, pp12–13; translation by Uphoff ).Von Liebig’s conclusion from a lifetime of research devoted to understanding soil
fertility was to emphasize the biological factors and processes within soil.
This perspective does not make chemical elements less important but rather
puts them into a living context. The interactions of the components and processes
of biological systems that have evolved over millennia provide a framework for
comprehending and managing soil systems. This does not suggest that ‘nature’
cannot be improved upon. But the admonition of Leonardo da Vinci: ‘Look first
to Nature for the best design before invention’, not only has a certain logic; a grow-
ing body of scientific evidence is explaining the merits attainable from complex
relationships and biodiversity within soil systems when they are enlisted on behalf
of agricultural production.
How sustainable any particular set of practices will be remains an empirical
question that deserves close and continuous study. Sometimes physical interven-
tions, such as profile modification, will enhance the soil’s biological processes and
capabilities. On the other hand, research has shown that one biologically oriented
practice, zero-tillage, by itself is not always the best practice (Govaerts et al, 2004).
Reduced tillage needs to be coupled with the use of mulch to create conditions for
plant, microbial and macrofauna growth that are optimal. While these can con-
tribute to denitrification, they contribute also N fixation. In complex systems, one
seeks net positive results, as many contradictory and offsetting processes are likely
to be involved. There is no reasonable basis for being opposed to ‘chemical inter-
ventions’ in soil systems as all of the processes discussed here involve chemicals, in
various forms. While some adverse effects of certain interventions can be identi-
fied, there are at the same time various chemical interventions that can be sup-
portive, and in many situations essential, for well-functioning agricultural soil
systems.
We began this book by affirming that all soil systems have these three interac-
tive facets – chemical, physical and biological. These are not subsystems or com-
ponents, but basically coequal dimensions that are conjoined in time and space.
Our focus and emphasis on this third facet has not tried to make it supreme but
rather to restore balance to soil system analyses and prescriptions, compensating for
past neglect. Everyone must recognize that there are some dynamic forces driving