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 Napiergrass, also known as elephant grass, resembles sugarcane
in stature and in methods of propagation. The grass is emerging
as a candidate bioenergy crop, but there are limited studies
available for napiergrass yield sensing, a technology that could
play an important role in implementing precision agriculture and
reducing harvesting cost. Alan Hansen, a professor in the U of I
Department of Agricultural and Biological Engineering, and Sunil
Mathanker, a postdoctoral researcher in the department, worked
with colleagues from John Deere and BP Biofuels to field test
the four yield-sensing approaches and document their correlation
to napiergrass yield.
In this study, a stem-bending yield sensor was developed to fit
a John Deere 3522 sugarcane billet harvester. Four load cells
were fitted between two parallel pipes to form a push bar. The
push bar was installed between the crop dividers about 1.2
meters above the ground and 1.5 meters ahead of the basecutter.
The study also investigated the hydraulic pressures of
basecutter, chopper, and elevator drives as indicators of yield.
Three pressure sensors were fitted to the inlets of the
hydraulic motors operating the basecutter, chopper, and elevator
on the John Deere harvester.
The sensor that measured stem-bending force was the most
accurate among the four methods tested. “What’s particularly
good about this sensor,” said Hansen, “is that you’re able to
measure yield at the point of entry. This is somewhat unique. In
combine harvesters, for instance, you’re monitoring a yield
sensor at a point much farther along in the flow of material,
where the grain is about to enter the tank at the top of the
combine. The delay between when the grain comes in and when it
reaches the point of measurement creates a potential for error,
and we have to come up with an estimate in relation to the time
lag. So having this look-ahead sensor right up front is of
significant value.”
While the look-ahead sensor showed the best correlation with
yield, Mathanker said there are issues, such as crop lodging,
harvester speed, and the ability of critical components to
respond to sudden changes in ground speed, that pose a challenge
for this sensing approach. Varietal characteristics, harvest
time, moisture content of the stems, soil conditions, sensor
height, and physical properties of the stems could also
influence the bending force experienced on a push bar.
Among the three hydraulic pressure-sensing approaches, the
chopper pressure showed the highest correlation with yield. A
reasonable correlation was found between the basecutter pressure
and yield, although in addition to yield, it was expected that
the basecutter pressure would depend on cutting height. Chopper
and elevator pressures were less affected by factors other than
yield compared to basecutter pressure.
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“Based on the results of this study,” Mathanker said, “the
stem-bending yield sensor showed potential for real-time napiergrass
yield prediction. It can also be used to control operating
parameters of the harvester [such as travel speed] and to generate
yield maps for precision agriculture. We believe this stem-bending
force sensing approach can be extended to other thick-stemmed
crops.”
Hansen and Mathanker published their findings in Computers and
Electronics in Agriculture 111 (2015). Co-authors of the paper were
H. Gan (Department of Agricultural and Biological Engineering,
University of Illinois at Urbana-Champaign), J.C. Buss (John Deere,
Thibodaux, LA), and J.F. Larsen (BP Biofuels North America, Houston,
TX).
The Energy Biosciences Institute is a public-private collaboration
in which bioscience and biological techniques are being applied to
help solve the global energy challenge. The partnership, funded with
$500 million for 10 years from the energy company BP, includes
researchers from the University of California, Berkeley; the
University of Illinois at Urbana-Champaign; and the Lawrence
Berkeley National Laboratory. Details about EBI can be found on the
EBI website.
[Leanne Lucas, University of Illinois
College of Agricultural, Consumer and Environmental Sciences]
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