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World’s Soil Resources

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Figure 15.2 Change in the percentage area of all land prepared for crops and pastures under different tillage practices in Australia,<br />

1996-2010 Source: SOE, 2011.<br />

Land management practices have improved significantly during the past few decades, due to better grazing<br />

practices, adoption of conservation tillage, enforcement of forestry codes and soil conservation measures in<br />

engineering (e.g. relating to road construction and urban development).<br />

Ground-based monitoring of management practices and land cover along with data on land-management<br />

practices (SOE, 2011) reveal a pattern of:<br />

• more careful grazing and maintenance of effective land cover at critical times of the year<br />

• improved adoption of conservation practices, especially across the cropping lands of southern Australia<br />

• an associated large decline in the amount of tillage in farming systems (Figure 15.2)<br />

New Zealand<br />

<strong>Soil</strong> loss by erosion is a major problem in many areas of New Zealand due to a combination of factors<br />

including soil type, topography and climate, as well as the type and associated intensity of land use (especially<br />

pastoral agriculture).<br />

Eyles (1983) provided the first systematic inventory of soil erosion in New Zealand and made the following<br />

observations and estimates. Surface erosion occurs mainly on the South Island. In 1983 sheet erosion<br />

affected 10 million ha of the country, while wind erosion affected 3 million ha (the total area of New Zealand<br />

is approximately 27 million ha). Mass movement occurred mainly on the North Island and slip erosion was<br />

estimated to affect 7 million ha. Fluvial erosion also occurred mainly in the North Island with rill and gully<br />

erosion estimated to affect 2 million ha. The study concluded that a total of 9 million ha of farmed land in New<br />

Zealand was at risk of significant erosion, although the level of risk was variable. The large scale afforestation<br />

of hill country and steep-land pasture since 1983 (see case study below) will have substantially reduced rates of<br />

soil erosion (especially sheet and slip erosion). However, forest harvesting results in significant soil disturbance<br />

and this will increase the risk of erosion when the first rotation forest is harvested and the second rotation<br />

established.<br />

Dymond (2010) analysed erosion rates in order to refine the national carbon budget because soil erosion<br />

in New Zealand results in the large export of sediment and particulate organic carbon (POC) directly to the<br />

sea. The North Island of New Zealand was estimated to export 1.9 (−0.5/+1.0) million tonnes of POC per year<br />

to the sea, and to sequester 1.25 (−0.3 /+0.6) million tonnes of carbon per year from the atmosphere through<br />

Status of the <strong>World’s</strong> <strong>Soil</strong> <strong>Resources</strong> | Main Report Regional Assessment of <strong>Soil</strong> Changes<br />

486<br />

in the Southwest Pacific

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