GIS Based Land Suitability Analysis and Mapping for Major Irrigation Methods for South Australia

Land suitability is a part of land evaluation to examine whether unit of land under consideration is fit for particular purpose or not. According to FAO (1990) land suitability is a process of matching the qualities of unit of land with requirement for a particular form of land use. The process of land suitability study may involve a number of activities –defining the land use requirement in one side, and determining characteristics and qualities of units of land in the other side, and finally matching the requirement with the quality of land units (FAO 1983; saremi et al. 2011). Ultimately, land will be classified or re-classified so as to allocate or reallocate for a particular use to achieve physical conservation of land resources, economic, or socio-political goals (FAO 1983; Yan-Su et al. 2006).

Land suitability studies can be conducted in different ways and for different purposes. In fact, the types land features or attributes to be studied, the scale of study, techniques, tools and procedures to be used would vary from study to study. However, majority of land suitability studies are related to features such as Soils Climate, hydrology, topography, Composite environmental, and Socio-economic data related to land units at different scales (Yan-Su et al. 2006). The history of land suitability studies show that techniques and tools in land suitability studies have been consistently and significantly being changed. From late 19 ^th to early 20 ^th century, hand drawn overlay techniques have been used. Later, ‘advanced’ overlay techniques of superimposing different transparent paper maps to trace suitability areas have been employed. These techniques have, then been replaced with ‘modern overlay’ techniques in which computers have replaced manual overlay operations. Finally, at this age GIS based land suitability mapping have taken the lion share of mapping activities (Malczewski 2004).

Technical procedures behind the mapping techniques to identify the suitable sites have also been varied with in a different as well as in similar areas of studies. But, the focus in here is on land suitability studies in agriculture, in general, and irrigation development, in particular. In crop production, identifying suitable geographic and climatic locations, agro-climatic zones of crops have been the major priority in land suability studies in different countries.

GIS based Suitability for a number of crops maps have been conducted in different countries especially starting from early 2000. Some of them are by Kalogirou (2002) in UK, for general cultivation and five specific crops (wheat, barley, maize, seed cotton, sugar beet), by Saremi et al. (2011) in Iran for three major crops and apple, by Mendas & Delali (2012) in Algeria for durum wheat, by Rabia (2012) in Ethiopia for Teff, maize, and wheat , by Deng et al. (2014) in north china for Alfa Alfa, and recently by Abraham et al. (2015) in Ethiopia for vegetable crops. Majority of these studies were made based on parametric land evaluation methods described by Syset al. (1991). Parametric evaluation uses land capability index calculated for particular unit of land based on ratings to land attributes such as soil texture, slope of land surface, soil depth, soil calcium carbonate content, soil electric conductivity, soil stoniness, and drainage properties. In fact, it is one of the physical land evaluation methods described by FAO in 1983 as algebraic combinations of land quality ratings. The others being the maximum Limitation method and Ad-hoc combination of land quality ratings (FAO 1983). Maximum limitation method is used for suitability assessment based on single critically important factor related to quality of unit of land. This method is most often used to exclude a particular land unit from evaluation because of critical issues.

While Ad-hoc combination method uses a decision rule flexible with situations based on subjective assessment of the assessor (FAO 1990). Similar to crop suitability studies, parametric method is widely used in suitability studies for different irrigation methods. However, the rating scales and some of the parameters are not similar to crop suitability studies. A number of papers have been published in GIS base land suitability mapping for irrigation methods from different parts of the world. Some of them are Briza et al. (2001) in Morocco, Bienvenue et al. (2003) in Senegal, Mbodj et al. (2004) in Tunisian, Barberis & Minelli (2005) in china, and Dengiz (2006) in Turkey (drip & surface) for drip and surface irrigation methods and Ayalew (2014) in Ethiopia for sprinklers and surface irrigation, and Albaji et al. (2013) in Iran for surface, sprinklers, and drip irrigation methods. All of these studies were based on parametric methods with no or little modification. Thus, it can be understood that the GIS based parametric land suitability map is most popular and highly acceptable method to the scientific community for at least last decade.

Identifying Land suitability for particular use is crucial step for proper land use planning and management. The available land resource a country could have can only be allocated or reallocated if the potential of land resource is well identified. With growing demand for food and fibre globally, efficient and effective expansion of irrigated farms over land resources is increasingly becoming very important especially for country like Australia which exports more than 65% its agricultural products produced in water scare conditions. Despite the fact that Australian agriculture is identified as one of the leading agricultural industry globally, irrigation has not been given sufficient attention (Future water 2015). Looking at the unreplaceable role of irrigation in Australian agriculture, a number of land suitability studies for different irrigation methods might be expected to have already been conducted. However, no relevant published materials have been available. Any ways, this study is aimed at applying GIS land suitability study for different irrigation methods, in addition to giving some insight for land owners, land planners, and policy makers. To this end, popular GIS based land suitability analysis for irrigation methods has been identified through literature review. It was found that parametric method is most popular Method being used in integration with GIS. Parametric method or Ccapability index is an overall physical evaluation of land units in terms of land physical parameters such as soil texture, soil depth, soil drainage properties, land slope, soil salt and calcium carbon content (FAO 1983, Albaji et al. 2013).So the results from such evaluation can be used for longer time because the physical land attributes are relatively permanent features of the land for longer period (FAO 1983). Parametric method integrated with GIS is becoming the most popular in recent years. The objective of this study was, thus, to develop GIS based land suitability maps for South Australia for different irrigation method using parametric method. For this end, the Soil and land scape map units (LANSLU) spatial data from South Australia water, environment, and natural resources have been used among some other land uses and elevation spatial data. It was identified that South Australia has extremely limited land resources that is highly suitable to any of the irrigation methods while some meaningful potentials for drip and sprinklers irrigation at different degree of suitability, from moderately to marginally suitable.

It is evident that most of the land mapping units (LMUs) in agricultural districts of South Australia are dominantly unsuitable for surface irrigation method. While there is meaningful size of land suitable for sprinkler irrigation method. The largest portion of land in agricultural district is highly suitable for drip irrigation method. Drip irrigation is highly recommended as priority irrigation method not only for the highest land suitability but also for extremely highest water efficiency which makes it more suitable for the driest state in the driest continent. It is recommended to refer to the maps provided to identify the suitability classes for particular land units for each irrigation method. For practical purpose, the particular or detail description of each land suitability classes, major limitations and the corresponding land management required well documented in FAO publications can be referred.

No government or private funding support was available for this research.