362 Ecological Restoration and Design
soil systems that come from outside, particularly climate and human interventions,
while appreciating explicitly the animation of soil systems that is endogenous.
3 Some Issues for Biologically Driven Soil System
Management
3.1 Optimizing the use of organic and inorganic inputs
One of the most important issues for the next decade or two as agricultural sys-
tems move toward more biologically framed management practices will be how
to optimize the use of inorganic soil amendments so that there is a positive-sum
effect on agricultural productivity. The principle is that of ‘pump-priming’,
where utilizing a small amount of resources can elicit a much larger flow of
desired resources. Where available soil nutrients are deficient, the practice of
adding inorganic fertilizers has been conceived initially as zero-sum, compensat-
ing for a deficiency.
When inorganic nutrients are introduced into soil systems, unless sufficient
organic matter is supplied to feed the soil biota and maintain levels of soil organic
matter, there is often, over time, a depression of soil biotic communities and their
processes that support many aspects of soil fertility. In such cases, plants in the soil
become increasingly dependent on inorganic inputs, because organic inputs are
diminished. A substantial amount of the nitrogen taken up by plants, by some
estimates 20–40 per cent, is cycled through nematodes and other fauna that occupy
middle ranks of the soil food web (Badalucco and Kuikman, 2001; Bonkowski,
2004). Much of this is forgone when inorganic amendments are made. On the
other hand, there can be positive-sum dynamics when organic inputs are com-
bined with inorganic amendments that maintain the nutrients, soil organic matter
and its biological processes that underpin soil fertility.
Short-term benefits from inorganic soil amendments are common. There can
also be long-term benefits such as the residual effect of phosphorus and lime appli-
cations. But the long-term productivity ensuing from such amendments should be
assessed empirically rather than simply assumed. Often when soil systems have
been primarily managed with inorganic nutrients (first-paradigm approaches) are
switched to more biologically based systems (second-paradigm approaches), there
can be a reduction in yields until the soil biological system has been redeveloped,
including stocks of soil organic matter and the diversity as well as abundance of
soil organisms. How to reduce the length and magnitude of such ‘transitions’ in
agricultural systems is one of the most important and practical research questions
for plant and soil scientists in the years ahead. The answers will vary, probably
widely, among soil systems and for different crops. The results reported from
ICRISAT are encouraging in this regard. But this remains a thoroughly empirical
question. Some rough generalizations can be formulated, but actual practices need