World’s Soil Resources

• Above-ground biodiversity is much better characterized than soil biodiversity and there are several
megadiverse districts and countries in the region.
• Areas with high above-ground biodiversity are likely to be similarly diverse below ground if their
environments were relatively stable throughout the Pleistocene (e.g. the moist forests of southwest
Western Australia, rainforests on the eastern escarpment of Australia, intermediate elevations in
Papua New Guinea, southern districts in the South Island of New Zealand). Some ancient landscapes
were submerged during this period (e.g. New Caledonia) and this most likely had an impact on soil
biodiversity present today.
• A range of pressures and stressors directly affect soil biota and some have already been discussed (e.g.
loss of soil carbon, acidification, physical disruption through cultivation or other means, intensification
of fire regimes). Large areas in the region have experienced these pressures and stressors. As a
consequence, they are most likely experiencing a loss of soil biodiversity.
15.5.5 | Waterlogging
No comprehensive survey or monitoring of waterlogging have been undertaken at the district or national
level in the region. Waterlogging is a significant constraint on agricultural production and extensive drainage
schemes were installed during the twentieth century, particularly in low lying alluvial areas in New Zealand
and eastern Australia. Texture-contrast soils with impermeable B-horizons are widespread in the pasture and
cropping lands of southern Australia. Waterlogging is a major limiting factor of crop production in southwestern
Victoria (McDonald and Gardner, 1987). Raised beds are sometimes used to minimize the impact of
water logging and enhance crop production.
15.5.6 | Nutrient imbalance
Nutrient imbalances are widespread throughout the more intensively managed landscapes of the region.
Some of these have already been outlined in relation to carbon balances and acidification (see below as well).
The focus here is on systems of land use where nutrient mining, depletion or accumulation may be occurring.
Nutrient mining refers to situations where there is a large removal of nutrients with minimal additions.
In Australia, this has occurred in some extensive, low-input farming systems. For example, Dalal and Mayer
(1986) document the decline in soil fertility over 70 years in areas used for dryland cropping in Queensland. This
extensive low-input system relied on the natural fertility of its predominantly heavy clay soils (Vertisols) but it
now requires fertilizer inputs to offset nutrient exports in harvested products.
Nutrient decline is occurring in other parts of the region although there are few reliable surveys and
monitoring systems except in New Zealand. The shortening of rotations in the shifting agricultural systems
of Melanesia caused by increased population is most likely causing nutrient decline but minimal evidence is
available. Nutrient decline is also likely to be occurring on marginal lands that are degrading due to processes
such as acidification and erosion. The magnitude of the nutrient loss has been documented in a few districts,
particularly where sediments and nutrients have a major environmental impact.
Nutrient accumulation is a more recent phenomenon in the region and the case study on New Zealand
(see below) explores several aspects. In most other Australian farming systems, fertilizer use has increased
and most nutrient imbalances are managed because of the economic consequences of over- or under-use.
In Australia, the use of nitrogen fertilizers has more than doubled in the last 25 years but application rates
are still moderate compared to more intensively managed systems in China, Europe and the United States.
Nutrient accumulation has occurred across southern Australia and elsewhere. In a few cases, environmental
impacts are significant (e.g. the case of the Great Barrier Reef mentioned earlier and the Peel-Harvey system
in Western Australia (e.g. Ruprecht, Vitale and Weaver, 2013).
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in the Southwest Pacific