INTERNATIONAL DECADE OF SOIL – FAVOURITE SOIL by John Martin Victoria JANUARY 2016
Marrakai Soil - Sodosol or Dermosol
During the International Decade of Soils, we ask a soil researcher to select his or her favourite soil.
John Martin, Soil Science Australia member, joined the Northern Territory Administration in 1964 and until mid 1967 worked on a number soil survey projects mainly in the Top End. He joined the Victorian Department of Agriculture in 1967 and from 1976 to retiring in 1993 he was responsible for the mainly soil survey activities of the Department’s Soil Unit. From then to the present time he has continued to work on soil related projects, mainly on a voluntary basis.
If you had to choose a special Australian soil type what would it be?
A Marrakai Soil - Sodosol or Dermosol
|Figure 1. Exposed surface of the subsoil (domes and columns) of a Marakai soil.|
Consideration of a Marrakai soil of the Top End may open an interesting can of worms on topics including classification , land use and even soil mapping. The areas concerned were delineated as Marrakai Land System units in the iconic 1946 Katherine-Darwin Land System Survey (1). These include the alluvial plains of the Adelaide, Margaret, McKinlay and Mary rivers. These areas are situated north east, east and south east of the Town of Adelaide River. The changing classifications of the Marrakai soils reflect the evolution of classification systems over that period and it may be interesting to briefly mention these. A description and analytical data of a Marrakai Type Profile were included in the 1956 CSIRO Soil Publication No.6 (2) which followed the Land System Report.
Emphasis was placed on the concept of the soil family (3) and related where possible to the Great Soil Group System (4). The families were grouped under the GSG system. A description of a soil family includes a range of morphological, chemical and environmental characteristics. The soil family has proved to be appropriate to the situation in the Top End. In the 1956 Report the Marrakai profile was classified as a Meadow Podzolic and the Land System soils were described as acid alluvial soils. The highest pH quoted in the only reported profile was 5.7. The CSIRO 1969 survey (5) divided the western Marrakai into three, the Fabian (grasslands), Flatwood (savannah woodlands) and the McKinlay Land Systems. The family concept was maintained and all profiles were coded to the Northcote Key (6), the official system at the time. The authors also grouped the families under the Northcote Key often to the Section level. In Atlas sheet 8 (7)
Northcote characterized the Marrakai Soils, his Va73 unit, as mottled hard setting
|Figure 2. Rice crop on a Marrakai Soil at Tortilla Flats circa 1965.|
yellow grey duplex (Dy3) and non calcareous gradational earthy fabric (Gn2). A 1993 Technote (8) by Wesley –Smith referred to a detailed 1982 survey by Olsen who again used Soil families and Great Soil Groups (9). Wesley-Smith briefly compared the 1982 units to three soil groups derived from a 1965 soil pH Reconnaissance Survey (10). My choice of a Marrakai Soil is a representative profile of the most difficult of the three groups e.g. texture contrast profiles with relatively shallow surfaces, see accompanying photo. The third group (Dermosols) were the most generally agriculturally attractive. Accepting the difficulty of classifying a profile originally described many years before the publication of the ASC System (11) this profile may be, strictly, a Dermosol although I prefer a Sodosol ! In the reference site the B clay % is not quite twice as high as that immediately above, e.g. had the B horizon clay% been 32 and not 29 the soil might have been a Sodosol.
What are the main properties of this soil type?
The soils of the group represented by that profile have shallow e.g. 15cm, loamy sand to sandy loam surface soils overlying hard domed columnar B horizons with variable textures. Surface soil pH is typically 6.5. Subsoil pH values rise to a typical 9.5. However the outstanding and dramatic features of the soils are the high pH and ESP values for subsoils and the very hard domed columnar B horizon structures. Subsoil permeability can be very low. An interesting feature with regard to human comfort is the cloud of very fine material which can result from surface soil disturbance e.g. vehicle traverse, under very dry conditions. It can permeate vehicles and even clothes.
Why do you find this soil type particularly interesting?
Reasons for my interest in this soil include the history of the efforts to classify and map it and its importance in current agricultural development. The discovery of this particular soil and closely related morphological soil types resulted in an urgent soil pH survey of that part of the original Marrakai land System later delineated as the Fabian and Flatwood Land Systems. The purpose was to determine the extent and any mappable subdivisions of the Solonetzic type soils. At the present time such a survey would not present any great problem but in 1965 in consideration of the circumstances at the time it was quite a challenge which I found more than interesting. Those of us who have carried out soil surveys over large areas may appreciate the following story. Some of the factors involved included the urgency (planning, field work and report within a few months) limited resources (one land rover and a loan of 1200 small format large scale air photos), access (limited number of tracks) and terrain. The north flowing rivers and water courses meant that lateral traverses were difficult particularly in southern areas towards the dissected foothills. Bush bashing with compass and shadow stick added a touch of adventure. Navigation without air photos would have been very difficult.
Do the properties of this soil type have consequences for its management, e.g. in terms of land use, soil quality and conservation?
Figure 3. General location of Plains with Marrakai Soils in the Adelaide River to Mary River Area.
Although notgreat inarea, the Fabian and Flatwood Land Systems total only about 2 000 km2, they are a significant zone with regard to future development. There is considerable variability in soil properties e.g. the texture contrast Solodized Solonetzic surface soils may vary from 15 to 40 cm in depth. The Solodic gradational soils have deeper surface soils e.g. 60 cm. For the texture contrast soils an agronomically significant feature is the very low permeability of the subsoils. However this property has been an advantage to some extent in rice production. Current research is concerned with this crop, see accompanying photo.
Can you tell us your most memorable story concerning this soil type?
In the early days with reference to life style, modis operandi and attitudes, Jason Hill (Soil of the Month- September) is absolutely spot on. I may be able to add to the gelignite story. I suspect that the character involved was a late friend of mine who, having blunted the prongs of many auger heads on the solonetzic domes would have taken fiendish delight in getting his own back on those ‘pesty’ structures. On one field trip in the southern part of the Marrakai we found ourselves hemmed in by a 10m drop to a creek bed to the east and rock walls to the south and west. In doing a U turn we did some damage including a broken axle. It took days to get back to Darwin. I don’t think any of us had heard of OH and S. On that subject administration attitudes towards field workers could be really interesting. On an earlier trip after being seriously bogged we were several days overdue. One fellow, new to the country was inclined to complain. Comments from the administration were along the lines of “If you fellows get yourselves into trouble in the bush you are expected to get yourselves out of it, you can’t really expect people here to stop work and go looking for you lot so you had just better get yourselves properly organised”. Incidentally as far as living off the land goes if one has to curry a magpie goose be wary because if you get it wrong it could be just about as palatable as leather. It was indeed a very different time.
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- Soils of the Katherine –Darwin Region, Northern Territory. By G.A.Stewart Soil Publication No.6 CSIRO Melbourne 1956
- Soil Survey Manual Agric. Hand b. No.18 USDA. 1951
- A Manual of Australian Soils 2nd ed. , C.G. Stevens CSIRO Melbourne 1956
- Lands of the Adelaide-Alligator Area Northern Territory. Land Research Series No.25 R.Story et.al. CSIRO ,1969
- A Factual Key for the Recognition of Australian Soils 2nd Ed. By K.H.Northcote. CSIRO 1965
- Atlas of Australian Soils Explanatory Data for Sheet 8 K.H. Northcote CSIRO 1968
- Some Observations on the Tortilla Plains Soil Types and their Interaction With Pasture ,Cattle and Rice by Rob Wesley-Smith Technote , DPIF Northern Territory of Australia 1993
- A Handbook of Australian Soils, H.C.T.Stace et.al. Rellim Publications for CSIRO and ISSS , 1968
- Soils Investigations S. Baseden and J Martin , Agricultural Branch Northern Territory Administration A. Rep. 1964-65
- The Australian Soil Classification Rev. e d , R.F. Isbell , CSIRO 2002
X Prospects of Agriculture in the Northern Territory. Report of the Forster Committee. Department of Territories. 1960