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CrC for irrigation FuturEs

The existence of spatial variability in the field means that the water requirements of different areas of a crop may not be the same. There is potential for saving water by variably applying water in response to real-time, site-specific irrigation requirement. however, real-time sensors need to be developed to measure real-time plant water stress at high spatial resolution.

For cotton, the best indicator of water stress is plant growth. A cotton plant adds a new node to the main stem every three days, so the distance between these nodes on the main stem indicates the vegetative growth of the plant. Internode length is an attribute measured by agronomists to identify how moisture stressed a cotton crop is. However, measuring internode length is a tedious manual task, and it would

WHEN AND WHErE TO WATEr? ASK THE PLANT, AuTOMATICALLycrc for irrigation futuresCheryl McCarthy, CRC for Irrigation Futures

be much better if the process could be automated.

Potential of machine vision Machine vision, which can measure automatic internode length, is one possibility for doing this. Machine vision involves the extracting of useful information in a scene from a two-dimensional projection of the scene, such as an image captured by camera.

A vision system has been designed to automatically measure internode length. The system features a camera enclosure that traverses the crop canopy. The enclosure comprises a video camera sitting behind a transparent panel, and uses the flexible upper main stem of the plant to firstly touch the plant against the transparent panel, and then smoothly and non-destructively move over the plant. When the main stem touches the transparent panel, it becomes a fixed object plane from which reliable two-dimensional geometry can be measured.

Software algorithms have been written to take the image sequences collected by the camera and then systematically identify the main stem, plant branches, and then nodes, which are the intersection of the branches with the main stem. From a sequence of detected node positions, the distance between nodes, or internode distance, can be measured. Using the developed process, the system has automatically measured internode

length with a standard error of 1.0 mm and correlation coefficient of 0.92. Calculations indicate that the algorithms can be performed in real time. A patent application has been lodged for this method and apparatus by the CRC’s company IF Technolofgies Pty Ltd.

This research represents a step forward in machine vision of plants in the field environment. Typically, automatic machine vision measurement of plant parameters in the field is restricted to whole-plant characteristics, such as plant height or plant spacing. Publicly reported research for the automatic identification of subplant features such as stems and nodes is presently limited to seedlings and controlled glasshouse environments.

The current research has demonstrated that a within-canopy camera enclosure is a suitable platform for automatic measurement of plant parameters in the field. Automatic internode length measurement has been successfully achieved.

The sensor may potentially be used in a real-time application, such as a variable-rate irrigation machine, and could be implemented at relatively low cost.

Figure 1. (top) Moving image capture apparatus; and (below) sample image from apparatus.

automatic conveyance of camera enclosure in a cotton crop.

Cheryl McCarthy is doing her PhD with the CRC for Irrigation Futures. As part of this research she is looking at the potential of using machine vision to identify when and where to water plants. Cheryl’s is doing this research on cotton crops being grown on the Darling Downs in Queensland.

ContraCtor’s CornEr

contractor’scornerdoing the job right the first time saves moneysince it was established in the 1980s, a priority for IAl (and before that, the Irrigation Association of Australia) has been elevating professional standards in the irrigation industry through training and certification. Only by demonstrating that we are an industry whose members have the requisite skills and knowledge in designing and installing systems can we be taken seriously as a profession. There is much anecdotal evidence of poor design and installation but this is the first time we have documented an example of this in the journal. let’s hope more people in our industry step up to the plate so the situation described below by James simpson-lee from watermatic Irrigation becomes a thing of the past.

Earlier this year Watermatic Irrigation was called in to rectify problems with an irrigation system installed in an over-55s residential development in Sydney. The system was apparently installed by an experienced irrigation installer.

What was the problem?When James inspected the site it was more a case of what were the problems rather than a problem! The entire system had many defects that were the result of extremely poor installation techniques. In part these problems stemmed from the fact that no design had been completed before the system was

installed. Some of the worst defects were:

• poor layout of system resulting from the lack of an initial design

• inadequate backflow prevention• pipe lines and cables not buried

sufficiently• solenoid valves installed above grade

level• rainwater tanks installed on their

side and not level• no installation of pressure reduction

valves, where required• generally lazy design and

installation.

rectificationThe job was brought up to a legal and a generally acceptable standard. However, no guarantee could be offered because the finished installation included some of the original work. The cost of the rectification work came to a total of more than $10,000.

Attention to quality saves moneyThis was an expensive exercise that could have been avoided if the head contractor had understood the benefits of engaging a quality contractor from the start of the process to manage the design, installation, preparation of as constructed drawings and maintenance of the project. The end result is that the end user has an adhoc system that has cost far more than it should.

tying hoses off, not burying pipelines and cables deep enough and a valve box not installed level with the ground.

Examples of what NOT to do when installing an irrigation system

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