When and where to water? Ask the plant, automatically This article was written by Cheryl McCarthy, CRC for Irrigation Futures. It was published in the Irrigation Australia Journal in Summer 2007. www.irrigation.org.au

1. CrC for irrigation FuturEs
crc for irrigation futures
WHEN AND WHErE TO WATEr? ASK THE PLANT, AuTOMATICALLy
Cheryl McCarthy, 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 automatic conveyance of camera enclosure in a cotton crop.
measured by agronomists to identify
how moisture stressed a cotton crop is. be much better if the process could be length with a standard error of 1.0
However, measuring internode length automated. mm and correlation coefficient of
is a tedious manual task, and it would 0.92. Calculations indicate that the
Potential of machine vision algorithms can be performed in
Machine vision, which can measure real time. A patent application has
automatic internode length, is one been lodged for this method and
possibility for doing this. Machine apparatus by the CRC’s company IF
vision involves the extracting of useful Technolofgies Pty Ltd.
information in a scene from a two- This research represents a step
dimensional projection of the scene, forward in machine vision of
such as an image captured by camera. plants in the field environment.
A vision system has been designed Typically, automatic machine vision
to automatically measure internode measurement of plant parameters
length. The system features a camera in the field is restricted to whole-
enclosure that traverses the crop plant characteristics, such as plant
canopy. The enclosure comprises height or plant spacing. Publicly
a video camera sitting behind a reported research for the automatic
transparent panel, and uses the identification of subplant features such
flexible upper main stem of the plant as stems and nodes is presently limited
to firstly touch the plant against the to seedlings and controlled glasshouse
transparent panel, and then smoothly environments.
and non-destructively move over the The current research has
plant. When the main stem touches demonstrated that a within-canopy
the transparent panel, it becomes a camera enclosure is a suitable platform
fixed object plane from which reliable for automatic measurement of plant
two-dimensional geometry can be parameters in the field. Automatic
measured. internode length measurement has
Software algorithms have been been successfully achieved.
written to take the image sequences The sensor may potentially be used in a
collected by the camera and then real-time application, such as a variable-
systematically identify the main stem, rate irrigation machine, and could be
plant branches, and then nodes, which implemented at relatively low cost.
are the intersection of the branches
with the main stem. From a sequence
Cheryl McCarthy is doing her PhD with the
of detected node positions, the CRC for Irrigation Futures. As part of this
distance between nodes, or internode research she is looking at the potential of using
distance, can be measured. Using the machine vision to identify when and where to
Figure 1. (top) Moving image capture water plants. Cheryl’s is doing this research on
apparatus; and (below) sample image from developed process, the system has cotton crops being grown on the Darling Downs
apparatus. automatically measured internode in Queensland.
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