Agriculture Reference
In-Depth Information
levels of available P with only small inputs of P in the form of rock phosphate. The P budget for
the biodynamic treatment was negative due to the removal of a hay crop (Penfold
et al.
1995).
Soil quality indices have been used to compare the effect of organic and conventional
farming systems on selected soil functions. In the Washington State apple trial, the lower soil
quality rating for the conventional treatment (0.78, compared to 0.88 for the organic and 0.92
for the integrated treatments) was attributed to lack of organic matter inputs (Reganold
et al.
2001). In the Apelsvoll trial (Eltun
et al.
2002), the conventional treatments ranked higher
than the organic treatments for the soil chemical and biological components of fertility
assessed. Within each management system, the mixed farming systems had higher overall soil
fertility than the arable rotations. However, for the soil function of minimising environmental
impact, including nutrient runoff and soil erosion, the organic treatments rated higher than
the conventional treatments (Eltun
et al.
2002).
Compared to organic livestock treatments in field trials, organic arable rotations may have
decreased mineralisable C and N as a result of the absence of manure applications (Wander
et
al.
1995), negative N budgets and greater reduction in soil N over time (Eltun
et al.
2002).
Results from the Apelsvoll trial indicated that mixed livestock-cropping systems may have
higher inherent fertility than arable rotations (Breland and Eltun 1999) because of increased
soil biological and physical fertility and lower N leaching (Eltun
et al.
2002). However, the dif-
ferences between livestock and arable rotations were reduced in organic systems because of the
use of green and animal manures (Breland and Eltun 1999). These studies demonstrate the
difficulty in making broad generalisations about soil conditions in organic farming systems
without taking into account specific practices and local knowledge of soil and environmental
conditions.
Conclusions
Organic farming systems have evolved globally on both chemical fertile and infertile soils, but
national and international organic certification standards have originated primarily in regions
with younger, chemically fertile soils. Whereas organic practices can improve soil physical and
biological fertility, consistent effects are not always found, and soil chemical fertility may be
reduced if inputs do not match those removed in produce, leading to mining of soil nutrients.
The inability of organic farming practices to increase organic matter (and soil biological fertil-
ity) in some highly weathered soils and semi-arid environments could lead to unsustainable
practices based on current certification standards. Simplistic adherence to national or interna-
tional organic standards that deal with soil fertility will not automatically lead to sustainable
organic farming systems without additional holistic management that takes into account all
aspects of the farm environment, including climate, topography and soil type. Problems are
most likely to occur if the soil is highly weathered and low in chemical fertility. This empha-
sises the need for local knowledge so that appropriate adjustments can be made in response to
a decline in components of soil fertility. Adjustments might include changes in commodity
and emphasis on long-term solutions that are preventative rather than reactive (Watson
et al.
2002a). The extent to which organic farming practices that are used to improve soil fertility
can be incorporated into conventional management systems may be a definitive factor in the
development of more sustainable farming systems overall.
Emerging areas of research, such as the focus on 'soil priming', together with nanoscale
approaches to soil processes, have the potential to allow more rigorous scientific investigation of
aspects of organic farming that have been claimed based only on anecdotal evidence. Converging
research in molecular microbiology, soil microbial diversity and increasing interest in soil amel-
iorants such as microbial cocktails, compost tea and relatively insoluble minerals has potential to
