Agriculture Reference
In-Depth Information
one member, part or facet will have an effect
on everything else' (Merrill, 1983). This is
illustrated best by the biotic pyramid of
Albrecht (1975; cited in Merrill, 1983). This
pyramid is composed of several layers, with
soil at the base and humans at its apex. Ac-
cording to this schematic, any degradation
of soil quality threatens the whole of civil-
ization, and even mankind itself; hence the
need for careful soil husbandry.
The Law of Return stems from the con-
cept of the 'living substances cycle', which
originated in ancient times and reappeared
in treatises on agriculture in the 16th and
17th centuries. A rupture of this principle is
one of the factors that have been suggested
in several historical research works to ex-
plain the collapse of civilizations, attrib-
uted to failures of their agriculture. The
question is still at the heart of critical issues
in terms of urban waste recycling (Magid
et  al ., 2001). According to this principle,
life can only be maintained provided living
beings, or at least the residues of their activ-
ities and their bodies, are recycled at each step
of the biotic pyramid. A crucial process is
thus the establishment of organic flows to
the soil to maintain its fertility. Since this
return is SOM mediated, Balfour (1944),
and above all, Rusch (1972), adopted a scep-
tical position towards what they termed
Liebig's 'rather naive theory', and developed
a partly rigorous (Balfour and Howard), partly
ideological (Rusch) analysis of the agroe-
cological role of SOM. Howard's opinion,
as  expressed in The Soil and Health (1952),
matches Balfour's holism, his causal inter-
pretation of the relationship between soil,
plant, animal and human health being an-
chored in the idea of a cycle of the proteins
and their quality between living beings. Even
if his opinion was to some extent ideological,
Howard (1940, 1952) wrote rigorous tech-
nical handbooks on the production of com-
post, which he termed 'manufactured humus'.
Over the past few years, there has been a
renewed interest in the scientific community
for holistic approaches to soil management,
as evidenced by the proliferation of scientific
meetings, research programmes (and con-
sequently publications) on the topic of 'soil
health'. An International Federation of Organic
Agriculture Movements was even created in
1972; its first international conference was
held in 1977.
Towards ecological agriculture (1992)
The era of an 'ecological agriculture' may be
seen to result symbolically from the 1992
Earth Summit in Rio de Janeiro. 'Sustain-
able development' came to global attention
with the publication of a report of the World
Commission on Environment and Develop-
ment (WCED, 1987) in which it was defined
as 'development that meets the need of pre-
sent generations without compromising the
ability of future generations to meet their
own need'. This clear congruence with en-
vironmental concerns about the impact of
intensive, high-input agriculture, coupled
with the failure to achieve persistent and
consistent results in many parts of the
world, notably in Africa, stimulated a sub-
stantial effort to find sustainable means of
agricultural production (Conway and Barbier,
1990), focusing obviously on the use of re-
newable natural resources. As regards the
management of soil fertility, this new ap-
proach generated substantial attention on
the manner in which organic matter and
biological processes were being dealt with
(Scholes et al ., 1994).
One of the key features in terms of sus-
tainable practices consists of managing soil
fertility through a combination of organic
matter (crop residues, compost or manure)
and mineral nutrient inputs (Pieri, 1992).
This rediscovery of the benefits of the an-
cient concept of the integrated provision of
nutrients became the mainstay of soil fertil-
ity at the turn of the 20th century ( Mokwunye
and Hammond, 1992; Palm et al ., 1997).
Maintaining and/or improving SOM status
is central to its philosophy. The scientific
challenge remains unchanged and aims at
extending the ecological principles beyond
the manipulation of the plants' components
(with indirect influence on the soil biota,
decomposition processes and humus dy-
namics as a consequence), to include a more
direct manipulation of the soil biota (Swift,
1998). Some success was obtained with
 
Search WWH ::




Custom Search