Defining precision irrigation: A new approach to irrigation management

Although the term precision irrigation is now quite widely used, often to mean drip irrigation, there is no commonly accepted definition or conceptualisation of the term, and no cohesive framework to guide research, development or adoption. This paper is reporting on a review of precision irrigation funded by NPSI. This review is considering the role of current irrigation application technologies in precision irrigation, variable rate applications, adaptive control, and the sensing and decision support requirements. Precision irrigation as a concept differs substantially from current practice. In this paper (which is a slightly expanded version of a research bulletin recently published by NPSI) we have defined it using precision agriculture principles. It is well acknowledged that precision irrigation involves the 'differential irrigation' treatment of field variation as opposed to the 'uniform irrigation' treatment that underlies traditional irrigation management. However, we contend that precision irrigation is much more, that it must be holistic in its approach, adaptive and applicable to all irrigation methods. INTRODUCTION Despite the widespread promotion and adoption of precision agriculture in dry land cropping systems, the concept of irrigation as a component of precision agricultural systems is still in its infancy, both in Australia and internationally. There is currently no cohesive framework available to guide research, development or adoption of precision irrigation and its associated sensing, control, and decision support technologies. This project is reviewing research in precision irrigation, existing technologies and the application of precision irrigation. It will assess the role of current irrigation application technologies in precision irrigation, variable rate applications, adaptive control and the sensing and decision support requirements. Opportunities for adoption, future research and extension needs will also be identified. The first stage of the project – conceptualizing and defining precision irrigation is summarised in this paper. The newness of precision irrigation means there has been very little discussion around the concept—and any research being conducted will certainly benefit from shared knowledge. WHAT EXACTLY IS PRECISION IRRIGATION? Drip irrigation is often regarded as epitomizing precise irrigation because of its ability to control application rate and timing. The traditional meaning of precise irrigation is about applying precise amounts of water to crops at precise locations (e.g. within the soil profile) and at precise times – but uniformly across the field. This traditional definition is still widely used, particularly in the commercial sector. An internet search of the term ‘precision irrigation’ brings up a large number of irrigation installers and equipment sales companies, particularly in the area of turf and drip irrigation installations. Precision irrigation as a concept differs substantially from this common usage. For this project, we are defining precision irrigation using precision agriculture principles. Presented at the irrigation and Drainage Conference 2009, Irrigation Australia Ltd, Swan Hill, Vic, Australia, 18-21 Oct 2009. 2 of 6 A review of the rather sparse literature on precision irrigation brings up a range of definitions, including: The accurate and precise application of water to meet the specific requirements of individual plants or management units and minimize adverse environmental impact (Raine et al., 2007). The application of water to a given site in a volume and at a time needed for optimum crop production, profitability or other management objective at the site (Camp et al., 2006). Applying water in the right place with the right amount (Al-Karadsheh et al., 2002). Irrigation management (depth, timing) based on crop need to defined sub-areas of a field referred to as management zones (King et al., 2006). There is a common element to all of these definitions, involving the 'differential irrigation' treatment of field variation as opposed to the 'uniform irrigation' treatment that underlies traditional irrigation management. Precision irrigation focuses on individual plants or small areas within a field, while the traditional practice takes a ‘whole-field’ approach. However, precision irrigation is much more than the precise application of water: • precision irrigation involves the optimal management of the spatial and temporal components of irrigation; • precision irrigation is holistic, it should combine seamlessly the optimal performance of the application system with the crop, water and solute management; • precision irrigation is not a specific technology, it’s a way of thinking, a systems approach. • precision irrigation is adaptive, it’s a learning system; and • precision irrigation is applicable to all irrigation application methods and for all crops at appropriate spatial and temporal scales. Other definitions of precision irrigation are informed by the large quantity of international research that has focused on variable rate technologies for pressurized irrigation systems, particularly centre pivots, for example: Precision irrigation now includes a spatially variable capability. To achieve such capability, an otherwise conventional irrigation machine would need variable-rate sprinklers, position determination, variable-rate water supply, variable-rate nutrient injection (probably), and variable-rate pesticide application (possibly) (Sadler et al., 2005). However, it is our view that variable rate technology, applied at the scale implied by this definition, is not an essential component of precision irrigation, rather it is one of the many tools that may be applicable in implementing a precision irrigation system. The concept of precision irrigation can be applied to all forms of irrigation application, with and without variable rate technology and such definitions significantly limit the scope and potential of precision irrigation. AIMS / GOALS OF A PRECISION IRRIGATION SYSTEM Spatial variability in crop production (for example Figure 1) occurs as a result of spatial and temporal variations in soil structure and fertility; soil physical, chemical and hydraulic properties; irrigation applications; pests and diseases; and plant genetics. It is argued that this variability can be managed and economic benefit from irrigation maximized by meeting the specific irrigation needs of individual management zones through a precision irrigation approach. Precision irrigation will potentially alter on-farm decision-making, and simultaneously achieve the multiple objectives of enhancing input use efficiency, reducing environmental impacts, and increasing farm profits and product quality.