Agriculture Reference
In-Depth Information
Chapter 2
Soil fertility in organic farming systems
Jennifer Davis and Lyn Abbott*, University of Western Australia, Australia
*Prof Lynette Abbott, School of Earth and Geographical Sciences, University of Western Australia, Nedlands,
Western Australia 6009, Australia. Tel: +61 8 6488 2499, Fax: +61 8 6488 1050, Email: labbott@cyllene.uwa.edu.au
Introduction
All farming systems depend on the maintenance of soil fertility for environmental and
economic sustainability. The effective management of soil fertility is based on understanding
processes associated with its chemical, physical and biological components, but greater
emphasis has traditionally been given to soil chemical fertility. Soils vary greatly in their
inherent physical and chemical characteristics and thus in their capacity to support biological
activity. Of course, agricultural practices also affect soil fertility but the magnitude of change
depends on specific soil and environmental conditions. Therefore, local knowledge is neces-
sary to interpret the effects of farming practices on soil fertility.
Although organic farming has features of 'sustainable' agriculture, it cannot be assumed
that organic management per se is more or less sustainable than some other farming systems
(Reganold et al. 1990, Kirchmann and Thorvaldsson 2000). While all organic farming systems
operate without the use of synthetic chemical inputs, many other practices used in organic
farming are employed on both 'organic' and 'conventional' farms (Gosling and Shepherd
2005). Many conventional farming systems effectively address issues related to sustainability
such as nutrient use efficiency, appropriateness of rotations to landform and soil type, conser-
vation tillage, biodiversity and use of legumes (e.g. Stork and Jerie 2003, Ridley et al. 2004).
Thus, there is a continuum in the level and nature of changes in soil characteristics associated
with agricultural management practices, rather than two distinct categories of 'organic' and
'non-organic' (Parr et al. 1983, Drinkwater et al. 1995). Consequently, the concepts of sustain-
ability and soil fertility management in organic farming systems have parallels in systems that
use synthetic chemical inputs.
A key feature of organic farming systems is that they are, by necessity, very dependent on
soil biological fertility, which in turn inf luences aspects of chemical and physical fertility.
Organic farming systems aim to create temporal and spatial diversity in plant, animal and
microbial life (Le Guillou and Scharpé 2000, IFOAM 2002, Treadwell et al. 2003). Particular
emphasis is placed on creating a diverse microbial community to maximise nutrient use effi-
ciency from poorly soluble fertilisers and promote beneficial soil physical processes (Watts et
al. 2001, Watson et al. 2002b). In contrast, those farming systems that primarily use synthetic
chemical fertilisers to enhance soil chemical fertility may bypass important aspects of soil bio-
logical fertility that could contribute to the chemical, as well as to physical fertility of soil
(Abbott and Murphy 2003).
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