Salinisation as a consequence of irrigation can occur as a result of the application of poor quality (i.e. saline) water or mobilisation of salts from rising water tables (i.e. caused by excessive groundwater recharge). In order to determine the threat of salinisation a project entitled “Understanding the salinity threat in irrigated cotton growing areas of Australia” was established in 1991. Phase I (Preliminary Studies) involved testing existing field techniques (i.e. electromagnetic induction – EM) to assess cause and management of subsoil salinity at the field level, in the lower Namoi valley. Phase II (Methods and Techniques) was aimed at extending these techniques by i) automating EM instruments such as the EM38 and EM31 onto a Mobile Electromagnetic Sensing System (MESS), ii) developing district scale EM investigations (i.e. EM38 and EM34) and iii) carrying out regional scale modeling, in the lower Namoi and Gwydir valleys.

Phase III (Implementation and Management-CRC11C) was aimed at implementing the field (i.e. MESS), district (i.e. EM38 and EM34 surveys) and regional (i.e. reconnaissance soil surveys) methodology developed in Phase II, in each of the major cotton-growing areas of central (eg. Macquarie valley) and northern (eg. Gwydir valley) NSW and southeast (eg. Macintyre valley) Queensland. This was achieved by:

a) initial consultation with various community groups (eg. Bourke Irrigators Association) to ensure research projects developed were consistent with natural research management issues in each cotton-growing area;

b) generate matching research funds through the Natural Heritage Trust and Salt Action Programs;

c) collection of EM34/38 data and soil information in the root- (0-2 m) and vadose- zones (2-12 m) to measure, model, map, manage and monitor soil salinisation processes.

The main outcomes of the research carried out are the collection of over 7,500 EM34 and EM38 measurements and 350 soil profiles (0-12 m sampled at 1 m intervals) in the seven cotton-growing districts across five valleys. As shown in this report the data collected has been used at the district level to map a) deep drainage risk areas, and b) spatial distribution of subsurface saline material, whilst on the field level the cause and management of a) soil salinisation and b) water logging.

In order to consolidate the data collected in Phase III, for improved natural resource management, a follow up project is required (i.e. Phase IV-Interpretation and Extension). The main aim of Phase IV is to interpret the information collected and develop new methods (i.e. groundwater modeling from piezometric data) for understanding how point source soil salinisation occurs in irrigated cotton-growing areas. From the information collected and modelled it is expected that best management options can be devised for improved natural resource management. This is particularly the case in the Bourke, Warren and Trangie districts, where irrigation salinisation is problematic. In addition, detailed EM surveys are required to understand at the field level what the appropriate management options are required for improved natural resource management.