Agriculture Reference
In-Depth Information
Table 7.1
Approaches to sense soil tilth
Sensing techniques
Authors
Non contact sensing techniques
Gamma-ray attenuation
Oliveira et al. (
1998
)
Image analysis and -processing
Bogrekci and Godwin (
2007a
)
Stafford and Ambler (
1990
)
Laser relief metering
Bertuzzi and Stengel (
1988
)
Destain and Verbrugge (
1987
)
Harral and Cowe (
1982
)
Refl ectance of visible-and/or infrared radiation
Bowers and Hanks (
1965
)
Orlov (
1966
)
Zuo et al. (
2000
)
Ultrasonic relief metering
Scarlett et al. (
1997
)
Contact sensing techniques
Horizontal mini penetrometer
Olsen (
1992
)
Strain gage on spring tine
Bogrecki and Godwin (
2007b
)
This would allow to adjust the
cultivating intensity
on-the-go or alternatively to
adapt the site-specifi c
seed-rate
in order to compensate for coarser seedbeds.
The traditional method to examine the clod size distribution is mechanical siev-
ing of soil samples. This method is laborious and probably completely unsuited for
on-the-go sensing in real-time. However, it is still used as the standard reference
method in research for the assessment of tilth. Many attempts to realize a sensing of
the clod size distribution in a more convenient way have been made (Table
7.1
).
The methods can be classifi ed into non contact- and contact techniques, depend-
ing on the physical principles employed. Up to now, none of these methods is used
in practical farming. And on-the-go sensing in real-time has been realized only with
either relief sensing by ultrasonics or with a strain gage on a spring tine of a cultiva-
tor. The latter principle is dealt with below in detail.
7.3.1.1
Principle of Tilth Sensing via Impact Forces Acting on a Tine
The basis of this method are the
impact forces
that act on a spring type tine during
secondary cultivation. These forces result from the collision of the tine with soil
clods. They can be recorded by measuring the distance, for which the tine is
defl ected because of the soil's resistance.
A rather simple method to sense the defl ection of the tine is the use of a strain
gage. The deformation of the tine is measured by bonding a small electrical conduc-
tor to this machine part. Since this electrical conductor is stretched, distorted or
compressed together with the tine, its current output changes. From this - after care-
ful calibration - the forces can be obtained.
There is a fundamental difference in the objectives of sensing the soil forces that
act on a tine or a cone depending on whether the control of either primary- or sec-
ondary cultivation is aimed at.
