Agriculture Reference
In-Depth Information
9.4.2 A
PPLICATION
OF
A
C
ROP
D
ENSITY
S
ENSOR
FOR
V
ARIABLE
R
ATE
N
ITROGEN
F
ERTILIZATION
OF
W
INTER
W
HEAT
The realization of precision agriculture requires site-specific nitrogen fertilization.
There are many researches on site specific fertilizing (Haar et al., 1999; Schwarz
et al., 2001; Wenkel et al., 2001). Variable rate fertilizer application maps can be
accurately generated on the basis of grid soil sampling. However, accurate mapping
requires the intensity of the cost and labor associated with sampling (Fleming et
al., 2000). Colburn (1998) developed a real-time Soil Doctor system to reduce the
expense of grid soil sampling. Equipped with both contacting and noninvasive sen-
sors, the system can monitor electrochemistry, soil complex resistivity, and soil con-
ductivity for transient fertilizer and seeding rate control as well as data management,
visualization, and interpretation. Hydro Agri offers a nitrogen sensor estimating the
required amount of nitrogen fertilizer on the basis of spectral analysis of reflectance
in plant populations (Marquering and Reusch, 1997). Günther et al. (1999) used a
laser-induced fluorescence technique for site-specific nitrogen application by esti-
mating the chlorophyll content in the leaves of grain plants. Ehlert (2000) developed
a mechanical sensor (pendulum-meter) for measuring plant mass of winter wheat,
winter rye, rice, and grass.
Abdullah et al. (2002) investigated the realization of sensor-based nitrogen
variable rate fertilization by a combination of pendulum-meter, tractor, and rear-
mounted spreader, and assessed agronomic effects. The pendulum-meter sensor was
examined in real time under practical conditions for the third application of nitrogen
to winter wheat. It was mounted at the front of a tractor. The rate for third application
of nitrogen within the winter wheat field was examined by the sensor, which consists
of a fertilizer spreader (Amazone ZAM MAXtronic), a modified CAN-Bus (ISO
11783) onboard computer (agrocom. ACT), and job calculator (Mueller-Electronic).
According to the measured pendulum angle, the fertilizing rate was stepwise linear
adjusted using a program in the job computer. Two different pendulum sensors car-
ried by a field vehicle were used to scan the field to check the vegetative growth of
wheat plants in growth stage milk ripeness. Yield measurements were achieved by
using a weigh-bridge as well as the yield monitors in two combine harvesters (New
Holland). Considering the triangular distribution pattern of a centrifugal spreader
and in order to minimize the problem of imprecisely distributed fertilizer, two passes
of full working width of a combine harvester were the references in the center of each
strip. The effects of site-specific fertilizing on the quality of grain were evaluated
by hand at points with different levels of fertilizing. The analyzed quality of grain
includes crude protein, protein quality, falling number, and thousand-kernel mass.
Ehlert and Domsch (2002) reported good results with
r
2
of 0.86 obtained for the
calibration of the pendulum-meter. A high spatial variability was obtained from the
pendulum-meter based map of plant dry mass distribution. Both pendulum meters
showed the same results—that there was no difference in the vegetative growth of
wheat plants for the different fertilizer rates, because of dry weather conditions and
late nitrogen application. A large spatial variability was observed from the plant
dry mass distribution. Although good weather conditions were observed with rains
occurring at the right time, the variable rate fertilization did not obtain a difference
