Agriculture Reference
In-Depth Information
provide evidence of complex processes of nutrient release in highly biologically active soils. Con-
tributions to soil fertility from activated biological processes are likely to be minimised in soils
that receive flushes of highly soluble nutrients as in conventional farming systems, but this may
also occur where high quantities of manure or poorly composted organic matter are used. Fur-
thermore, organic farming practices that merely mimic the emphasis on 'nutrient replacement'
commonly used in conventional farming systems are unlikely to show the quantitative and qual-
itative changes in soil biological fertility necessary to make them sustainable.
Finally, the concept of 'sustainable yield' for a particular location may have greater poten-
tial to be explored in organic farming systems than in conventional systems. This is a complex
question because in practice, production can be achieved even in the absence of soil (e.g. in
hydroponics). Generally, chemical inputs into conventional agricultural systems are relatively
unlimited (except by cost) and they can override potential contributions by some biological
processes (Abbott and Murphy 2003). This is less likely in more nutrient-limited organic
farming systems where the manipulation of nutrient cycling through management of soil
organic matter has greater consequence. In this situation, the sustainability of the soil resource
for defined conditions (commodity, management practice, climate and soil type) can be esti-
mated without the possibility of 'overfertilisation' extending production to a level that might
cause one or more forms of land degradation. It is not usual to consider productivity as being
'too high' in any farming system, but this could be the case when high levels of fertilisation or
soil disturbance lead to nutrient loss through leaching or soil erosion. Management practices
that establish a long-term balance among the three components of soil fertility are likely to be
essential for calculating theoretical sustainable yield for any agricultural land use.
References
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Murphy, D.V. (eds)
Soil Biological Fertility - A Key to Sustainable Land Use in Agriculture
.
Kluwer Academic Publishers, the Netherlands. pp. 1-15.
AQIS 1998.
National Standard for Organic and Bio-dynamic Produce
. Australian Quarantine
and Inspection Service (AQIS), Canberra.
Bakken, A.K., Gautneb, H. and Myhr, K. 1997. The potential of crushed rocks and mine tail-
ings as slow-release K fertilisers assessed by intensive cropping with Italian ryegrass in dif-
ferent soil types.
Nutrient Cycling in Agroecosystems
47: 41-48.
Bakken, A.K., Gautneb, H., Sveistrup, T. and Myhr, K. 2000. Crushed rocks and miner tailings
applied as K fertilisers on grassland.
Nutrient Cycling in Agroecosystems
56: 53-57.
Barker, W.W., Welch, S.A. and Banfield, J.F. 1997. Biogeochemical weathering of silicate miner-
als. In: Banfield, J.F. and Nealson, K.H. (eds)
Geomicrobiology: Interactions between
Microbes and Minerals
. Mineralogical Society of America, Washington. pp. 391-428.
Barrow, N.J. 1985. Comparing the effectiveness of fertilisers.
Fertiliser Research
8: 85-90.
Barrow, N.J., Malajczuk, N. and Shaw, T.C. 1977. A direct test of the ability of vesicular-arbus-
cular mycorrhiza to help plants take up fixed soil phosphate.
New Phytologist
78:
269-276.
Berry, P.M., Sylvester-Bradley, R., Philipps, L., Hatch, D.J., Cuttle, S.P., Rayns, F.W. and Gosling,
P. 2002. Is the productivity of organic farms restricted by the supply of available nitrogen?
Soil Use and Management
18: 248-255.
Bloem, J., Lebbink, G., Zwart, K.B., Bouwman, L.A., Burgers, S.L.G.E., de Vos, J.A. and de
Ruiter, P.C. 1994. Dynamics of microorganisms, microbivores and nitrogen mineralisa-
tion in winter wheat fields under conventional and integrated management.
Agriculture,
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51: 129-143.
