Agriculture Reference
In-Depth Information
These
seasonal maps
can serve as control instruments for just a crop season or a
rotation of crops. Properties that lend themselves for these maps are
e.g.
the lime-,
phosphorus- and potash requirement of soils as well as the weed infestation. Though
it may be reasonable to keep these seasonal maps for long-term records, their use as
control devices is temporally limited.
Finally there are the
transient soil- and crop properties
. To these belong the
soil water content, the nitrogen status and fungal diseases of crops. The short-term
validity of these soil- or crop properties calls for immediate action, hence for proxi-
mal on-the-go control in real-time. So the control mode should fi t to the temporal
stability of the respective properties or their sensed surrogates. It is possible to map
the site-specifi c situation of these soil- and crop properties simultaneously as well.
However, for these transient properties, such a mapping procedure seems more
reasonable when the sensing occurs in a remote mode from satellites instead of a
proximal mode from tractors or vehicles.
The needs as to the frequency of sensing for these transient properties may be
quite different. The moisture content of soils and the water supply of crops that
depends on this are rather critical factors for high yields. Hence ideally, both factors
should be monitored throughout the growing season with sensing intervals of not
more than a few days or weeks. Such a procedure does not lend itself to proximal
sensing from vehicles or farm machines as long as these need drivers. Instead of
this,
moisture monitoring
should be aimed at via remote sensing from satellites in
a similar way as georeferencing is being done. Principally, radar waves can do this
independent of cloud covers. However, the processing of the signals still must be
improved and the number of radar satellites does not suffi ce yet. There are alternatives
to remote water detection via radar waves, such as remote or proximal sensing by
infrared radiation and fi nally proximal sensing by electrical capacitance. None of
the methods mentioned presently are state of the art.
It can be expected that many farming operations in the future will include a
site-specifi c control system.
In
primary cultivation
, the depth of operation is the main objective of control.
Soil properties that can supply signals for a site-specifi c control are texture, organic
matter content, slope and eventually the hydromorphic situation. For
secondary
cultivation
, the tilth or the break-up of the seedbed is an important criterion since it
affects the emergence of crops. This seedbed property can be sensed in a site-specifi c
mode rather effectively by means of the standard deviation of forces that act on a
tine of the cultivating implement. In site-specifi c
sowing
, the seed-density per unit
area of the fi eld and the seeding depth are objectives of control. For the seed-density,
the control should primarily be oriented at the soil texture. Especially in regions with
continental climate, the seeding depth should be such that the seeds are deposited
underneath the drying front of the soil. Hence the vertical distance of this drying
front from the soil surface must be sensed. Approaches to do this rely either on
near-infrared radiation or on electrical resistance.
Site-specifi c
fertilizing
relies either on the removal of nutrients by preceding
crops or on the supply in the soil as well as in the growing plants. The removal
of nutrients by preceding crops can be determined via site-specifi c yield sensing.
