Precision Agriculture, 4, 139±148, 2003
2003 Kluwer Academic Publishers. Manufactured in The Netherlands.
On-line Sensor Pendulum-Meter for
Determination of Plant Mass
D. EHLERT firstname.lastname@example.org
R. ADAMEK email@example.com
Institute of Agricultural Engineering Bornim (ATB), Division Engineering for Crop Production,
Max-Eyth-Allee 100, D-14469 Potsdam, Germany
Abstract. A vehicle-based mechanical sensor (pendulum-meter) was developed to measure the plant mass of
crops. For testing under defined conditions, a dynamometer with pendulum-meter, sensory and electronic
equipment was developed. The ability and accuracy of the sensor for measuring plant mass in different crops
(winter wheat, winter rye, grass, rice) and different growth stages are discussed in this paper. Parameter trials
were done for optimising pendulum parameters. The correlations between plant mass and pendulum angle
measurements were good (r
< 0.89) for all pendulum parameters, with no significant differences between
suitable parameters. The speed ofthe pendulum-meter causes a linear increase ofthe measured pendulum angle.
The pendulum-meter is ofsimple construction.
Keywords: precision farming, plant mass measurement, pendulum-meter, assessment
Information about the distribution of plant mass growing in a field is a prerequisite to
precision agriculture. For time-efficient, non-destructive and labour-saving measure-
ments, sensors are needed which can determine and predictÐpreferably on-lineÐthe
plant mass and yields ofcrops. Determination ofspatially variable plant mass is
important for optimising inputs of agro-chemicals, and improving management and
Surveying heterogeneity in plant mass distribution is possible by both aerial
photography (Pearson et al., 1976; Tucker et al., 1981) and vehicle-based methods.
(Jaynes et al., 1995; Hansen and Jorgensen, 2001).
Measuring reflectance, spatial variation in canopy density can be estimated for site
specific pesticide application in cereals (Christensen et al., 1997). Paice et al. (1999)
investigated three techniques for estimating local crop plant density in a winter cereal
crop: tiller count sampling, red/NIR radiometry and image analyses ofstill photographs.
Attempts have been made to estimate yields by measuring sward height (Hutchings
et al., 1990), disc-meters and plate-meters (Castle, 1976; Earle and McGowan, 1979;
Scrivner et al., 1986; Virkaj
arvi and Matilainen, 1994) and capacitance meters (Gonzalez
et al., 1990).
The plate meter consists ofa PVC rod surrounded with a round polystyrene foam plate
with a diameter of0.6 m. The rod is placed perpendicular to the grass until it rests on
the ground. Doe to its own weight, the plate sinks down and compacts the grass. Then the