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Soil and Land Assessment of the Southern Part of Flying Fox Station for Irrigated Agriculture. Part A: Land Resources and General Land Capability.



Soil and Land Assessment of the Southern Part of Flying Fox Station for Irrigated Agriculture. Part A: Land Resources and General Land Capability.

Other title

Agricultural Land Suitability Series, Report 14A


Andrews, K; Burgess, J; McGrath, N; Wright, A; Walton, S; Northern Territory. Department of Environment, Parks and Water Security


Hill, J.V.


E-Publications; E-Books; PublicationNT; Technical Report No. 3/2021




Flying Fox Station; Roper River Region


This report presents findings from a 52 938 ha soil and land resource mapping investigation of the southern part of Flying Fox Station, in the Roper River Region of the Northern Territory. While the study area was primarily selected because of its diverse geology, terrain and soils, it is also representative of the central Roper River region, and findings from the investigation will underpin and guide future agricultural development in the region.


Made available by via Publications (Legal Deposit) Act 2004 (NT)

Table of contents

Executive Summary; 1. Introduction; 2. Previous land resource investigations; 3. Methodology; 4. Climate; 5. Geology; 6. Landscapes; 7. Land units; 8. Land capability assessment; 9. Land management; 10. References; Appendices.




soil survey; land resource assessment; land units; land capability assessment

Publisher name

Northern Territory Government

Place of publication





Technical Report No. 3/2021


208 pages : colour maps and illustrations ; 30cm

File type





Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



Related links

http://www.ntlis.nt.gov.au/metadata/export_data?type=html&metadata_id=6589A5D125EFB385E050CD9B2144202B; https://hdl.handle.net/10070/820014 [Report_print_Soil Land Assessment Flying Fox - Part A Land Resources General Land Capability]; https://hdl.handle.net/10070/820013 [Report_screen_Soil Land Assessment Flying Fox - Part A Land Resources General Land Capability]; https://hdl.handle.net/10070/829192 [Soil and Land Assessment of the Southern Part of Flying Fox Station for Irrigated Agriculture. Part B: Digital Soil Mapping and Crop Specific Land Suitability]

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Soil and Land Assessment of the Southern Part of Flying Fox Station for Irrigated Agriculture Part A: Land Resources and General Land Capability 91 Land Unit 9d Analytical data for Land Unit 9d is limited to pH and salinity data from field sites, and exchangeable cation data from Site 37. Additional soil chemistry and physical attributes described below come from Land Unit 8d (Site 5), which has similar soil morphology, parent material and clay mineralogy. Soil pH and salinity field sites pH, EC and Cl analyses (see Appendix 2) indicate the surface soil is slightly alkaline (pH range 7.6-7.7) and subsoil horizons moderately to strongly alkaline (pH range 8.2-9.0). Both mean and median salinity levels are very low (mean ECe 0.26-1.73 dS/m) to about 1.0-1.1 m but increase gradually to low or moderate levels (mean ECe 3.38-5.90 dS/m) below this depth. Calculated ECe values are below the critical root zone threshold (ECe 6 dS/m), and median salinity curves suggest the soils long-term wetting front and effective rooting depth (ERD) are >1.5 m. Identified sodicity constraints (see sodicity comments below) are not critical to crop growth and do not limit ERD. Soil chemistry Site 37 (LU 9d), Site 5 (equivalent LU 8d) Organic fertility (carbon, nitrogen), and macronutrients (phosphorous, sulfate) and micronutrients (copper, zinc) are higher than the very low to moderate levels recorded for Land Unit 8d because of local alluvial concentration. Calcium and potassium levels in the surface soil (0-0.1 m) at Site 37 are high to very high. Similarly, CEC values are high to very high (36-41 cmol/kg) throughout and indicate significant capacity for nutrient retention. The presence of gilgai, surface cracking, self-mulching behaviour and strong lenticular structure suggest the clay fraction is of mixed mineralogy with a high proportion of montmorillonite, is highly reactive and has significant shrink-swell characteristics. ESP data at Site 37 indicates profiles are non-sodic (ESP <6%) to about 0.5 m, moderately sodic (ESP 6-15%) to about 1.0-1.1 m and strongly sodic (ESP 17%) below 1.0-1.1 m. Physical soil characteristics Site 37 (LU 9d), Site 5 (equivalent LU 8d) Soil profiles are very deep (>1.5 m), slowly permeable and moderately well-drained. Surface horizons to about 0.1 m (A1/B1) are strongly structured (granular grading to blocky), and exhibit strong cracking with a moderately to strongly self-mulching undisturbed surface condition. Laboratory measured clay contents from Site 5 (Land Unit 8d) are moderately high to high (41-48%) and uniform throughout. Fine sand (35-42%) and silt (13-16) fractions are only moderate. Field textures however, suggest that subsoil clay contents in Land Unit 9d may range from ~40-70% depending on local depositional characteristics. Laboratory dispersion (R1) will follow sodicity trends measured at Site 37, with very low to low levels (R1 <0.5) in the upper profile (to about 0.5 m), low or moderate levels (R1 0.5-0.8) to about 1.0-1.1 m and high levels (R1 >0.8) below this. Cation chemistry is strongly calcium dominant throughout however and will act to counter any dispersive behaviour in the lower subsoil. Constraints to agricultural development Soils within Land Unit 9d are very deep (>1.5 m), moderately to strongly self-mulching, black cracking clays on doleritic derived alluvium. They are characterised by low to moderate fertility, high nutrient holding capacity, moderate to strong lenticular structure, high to very high clay contents (range ~40-70%) and significant clay activity. Important constraints include regular flooding, minor gilgai (VI <0.3 m) and increasing salinity and sodicity in the lower subsoil (below 1.0 m). General land capability outcomes Land Unit 9d (Class 4 variably constrained) is considered to have limited development potential. Severe to extreme constraints, most notably regular flooding, are known to affect the unit, but are unpredictable in their severity (ranging from locally absent to moderate, severe or extreme) and are subject to significant spatial variability. Field observations confirm the presence of arable soils in locally un-constrained pockets however and suggest limited paddock scale development opportunities may exist. The extent and distribution of such opportunities is unpredictable at the current scale of mapping and detailed on-ground soil investigations would be required to accurately locate and quantify such prospects. Land capability criteria and contributing data are presented in Appendices 4 and 5 and discussed further in Chapter 8. ECe (dS/m) 0 5 10 15 20 25 30 35 0 0_3 g o_6 .r:. ... c. 0 o_g 1-2 1-5 -- Individual site Root zone 1h resh old I--, Standard deviation

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