Agriculture Reference
In-Depth Information
Table 14.2
Areas of Soil Orders in New Zealand
Area (km
2
)
% of Total NZ Soil Areas
Allophanic Soils
13,670
5
Anthropic Soils
180
<1
Brown Soils
108,450
43
Gley Soils
7,120
3
Granular Soils
2,930
1
Melanic Soils
3,220
1
Organic Soils
2,260
1
Oxidic Soils
440
<1
Pallic Soils
30,910
12
Podzols
32,870
13
Pumice Soils
17,210
7
Raw Soils
7,090
3
Recent Soils
14,020
6
Semiarid Soils
2,220
1
Ultic Soils
7,620
3
soilÏenvironmental relationships and had proven utility, and deÝned them, respectively, as the Pallic
Soils and Brown Soils.
Discrimination between the extensive (Table 14.2) Pallic Soils and Brown Soils orders was
based on the effects of relative differences in leaching and weathering. The Pallic Soils had relatively
low contents of dispersed secondary iron and aluminium oxides expressed in low phosphate
retention values (Hewitt, 1993a) of less than 30%, with consequent pale colors (hence the name
ÓPallicÔ). Fragipans are ubiquitous in soils in loess on stable sites. The Brown Soils have relatively
higher content of dispersed secondary iron and aluminium oxides expressed in phosphate retention
values of 30% or more. They are generally more acid with lower base saturation than the Pallic Soils.
CONCLUSION
Development of a soil classiÝcation system requires a multitude of decisions. There is no
shortage of opinions offered by those involved, and there is pressure to make ad hoc decisions that
may have the effect of distorting the logic of the system. A clear statement of purpose and widely
agreed-upon principles, focused on at debates during the development of the New Zealand Soils
ClassiÝcation, greatly aided decision making. In New Zealand, we were fortunate in having a soil
science community that was supportive and enthusiastic, and it was this support that has resulted
in a system that shows it can achieve its purposes.
REFERENCES
Avery, B.W. 1980. Soil classiÝcation for England and Wales (higher categories). Soil Survey Technical
Monograph 14. Rothamstead Experimental Station, Harpendon, UK.
Canada Soil Survey Committee. 1978. The Canadian system of soil classiÝcation. Research Branch, Canada
Department of Agriculture. Publication 1646.
Childs, C.W. and Clayden, B. 1986. On the deÝnition and identiÝcation of aquic soil moisture regimes.
Aust.
24:311Ï316.
Clayden, B. and Hewitt, A.E. 1993. A new system of soil horizon notation of New Zealand soils.
J. Soil Res.
Catena
19:405Ï410.
Clayden, B. and Webb, T.H. 1994. Criteria for deÝning the soilformÐthe fourth category of the New Zealand
Soil ClassiÝcation. Landcare Research Science Series 3, Manaaki Whenua Press, Lincoln, New
Zealand.
