Download Images key to understanding roots of plant fertiliser

Nutrients in the paddock Cropping |
Focus: The long-term aim of research into
wheat root development and fertiliser
placement is to improve yields.
Catherine Norwood looks at
new-generation technology
allowing researchers to see
how root systems develop
in the ground — and the
impact of the placement and
concentration of nutrients,
particularly phosphorus
At a glance...
▸▸New technology is allowing
researchers to take better images
of plant roots as they grow
▸▸The images will help identify
plant root growth in response to
different fertiliser placements
and concentrations
▸▸It will improve advice to
growers on more efficient
applications of fertiliser
www.kondiningroup.com.au
Images key to
understanding roots
of plant fertiliser use
N
ew computer-based technology
is being developed to help
researchers determine the most
effective placement of nutrients to
stimulate plant root growth and increase
crop yields.
The technology produces something
like a CATscan for plant roots, allowing
researchers to see how roots develop “in
situ”, and how growth relates to the
placement and concentration of nutrients
— phosphorus in particular.
Dr Chris Guppy at the University of
New England (UNE) is leading the
GRDC-supported project, which is
working on automated techniques to
allow computers to trace root growth
from three-dimensional images.
Computerised processing of imaging
would allow for faster analysis of data
from a greater number of trial samples.
The initial imaging work was used
wheat plants grown in vertisol soils,
raised in glasshouse conditions.
Dr Guppy said tracing plant roots was
more difficult than identifying bone and
organs from a CATscan.
“Plant roots are mostly water and
because these processes rely on the
density of the material being scanned it
can be very difficult to separate roots from
soil and soil moisture,” he said.
“A variety of techniques can be used to
prepare samples for imaging, including
drying out the soil.
“But we haven’t done too much of this
because we are trying to image the plant
as it would be in the paddock.
“Once a primary root is identified we
want the computer to follow that root to
the end of every branch. But sometimes
the roots become disconnected as they
squeeze between the pixels that make up
an image.
“Our brains are capable of the spatial
prediction that allows us to work out
where the root has gone, even though we
can’t see it, but you have to tell a computer
to generate probabilities about where the
root has gone.”
Mathematicians
and
computer
programmers are collaborating with soil
and plant scientists on the project and Dr
Guppy said the images being generated
at UNE were amongst the best in the
world at the moment; other researchers
were able to track smaller roots, but the
images were not as clear.
Others involved in the research were
Dr Mike Bell, at the Queensland Alliance
for Agriculture and Food Innovation and
UNE PhD candidate Richard Flavel, who
has already received an award from the
International Plant Nutrition Institute for
his work on the project.
Images have already shown increased
plant root growth in response to
phosphorus enriched soils, with greater
root density in these areas.
The long-term outcome
of the research was to
improve the efficiency
of nutrient application
for growers.
Dr Guppy said many Australian soils
were deficient in phosphorus, and he
expected the results would be more about
changing the way phosphorus was
applied, rather than actually reducing the
rate of application.
He said at the moment growers in the
northern grain growing region applied
No. 242 March 2012 Farming Ahead
49
| Cropping Nutrients in the paddock
phosphorus at rates of around six
kilograms per hectare. Most of this was
applied as MAP or DAP starter fertiliser
at sowing.
Other trials suggest that
making phosphorus
available deeper in the soil
is important, particularly
in no-till systems.”
This included findings that up to 50
per cent of a plant’s phosphorus
requirements were taken from the top
10cm of soil, a further 30 per cent from
10–30cm deep, and 20 per cent taken
from below 30cm.
But there was increasing soil
stratification of nutrients in many places
which could result in a 'positional
deficiency' of phosphorus.
Passing the test: Researcher Richard Flavel
with wheat raised in the greenhouse to test
root growth response to phosphorus.
“So the plants can’t access it. Growers
need to find some way to ‘refill the tank
underneath’ where the soil is wetter and
the roots are more active.”
Plant growth
“There’s plenty of phosphorus in the
soil, but it’s often concentrated in the top
two centimetres and that’s not where the
plant’s roots are active, particularly if the
soil has dried out,” he said.
In addition to providing valuable
information for growers, Dr Guppy said
he hoped the research would contribute to
a better understanding of the fundamental
science of plant root growth.
Revealed: Wheat root growth in response to
a granule of phosphorus placed in a similar
depth in a similar pot.
Growth: A wheat root responds to a band of
P placed between the blue dots in a column
about a foot long. The phosphorus was
evenly distributed between the blue dots.
This included information about how
much and where plants 'decide' to allocate
energy to root growth.
A plant can invest up to half its energy
in creating roots, but the science behind
how the allocation between roots and
shoots is determined is still uncertain,”
he said.
This included the role of nutrients in
triggering different plant root responses.
He said there were two schools of
thought about below-ground priorities
for carbon allocation by roots.
The botanical and ecological approach
was that when plants found a patch of
nutrients, a dense patch of roots developed
to exploit the nutrients.
That came at the expense of developing
a broader root system but still allowed the
plants to invest in growth above ground.
The agricultural view was that plants
would exploit nutrients in a patch,
allowing a more expansive root system to
search for further nutrients and water.
These additional root structures then
allowed greater above-ground growth in
the annual systems common to
agriculture.
“Maybe that’s the difference between
annual and perennial systems; we don’t
really know,” Dr Guppy said.
“But there are basic questions about
whether the allocation of growth within
root systems is essentially fixed, or
whether we can adjust plant root
investment through nutrient placement
to increase overall grain and shoot
yields.” GRDC RESEARCH
50
Farming Ahead March 2012 No. 242
Chris Guppy
(02) 6773 3567
[email protected]
www.kondiningroup.com.au
Photos: University of New England
“But if we can stimulate root growth
response from lower levels of starter
phosphorus it gives growers the chance
to place phosphorus at different points
in the soil profile and get potentially
greater uptake of the applied fertiliser,”
Dr Guppy said.