Agriculture Reference
In-Depth Information
radiation, does not get through clouds. Hence the concept of remote sensing based
on infrared reflectance would be risky for regions with maritime climate.
The restrictions that result from clouds do not exist for remote sensing via
radar
.
However, remote water sensing of soils or crops via radar still is in an experimental
state. This applies especially to water sensing in crops, which would be preferable,
because it automatically takes into account any interaction between soils and roots
on the supply of plants.
9.4.11
Benefits, Costs and Economics
9.4.11.1
Beneits
The potential benefits from site-specific nitrogen application can vary between
•
higher yields in masses of product per ha
•
savings for nitrogen fertilizer
•
better conditions for harvesting the crop
•
better qualities of the harvested product
•
less leaching of nitrogen into ground-waters.
Which of these possible benefits dominates, might depend on the crop, the varia-
tions in soil properties and weather, the control algorithm as well as on the time
within the growing season when the site-specific technique is used. Hence for com-
parisons of uniform- versus site-specific nitrogen applications, a variety of results
might evolve.
Higher
yields
in masses of product per ha can be expected if the average nitrogen
rate for site-specific application is about the same - and hence not lower - than with
uniform fertilizing. In field experiments with site-specific and uniform application,
this is not easy to obtain, since the average rate with site-specific fertilizing is not
known precisely beforehand. Another prerequisite for higher yields is site-specific
application within a rather early vegetation stage,
e.g.
EC or BBCH 30-40 with
small grains.
The comparisons of site-specific and uniform applications in Fig.
9.40
are based
on approximately the same average nitrogen rate and early dressings of winter-
wheat. The site-specific applications were controlled by reflectance sensing. It can
be seen that for the location Raguhn the yields hardly were influenced. The reasons
for this probably are uniform soil properties or low rainfall in the growing season.
The other 16 locations resulted in a
mean yield increase of 4.1 %
.
However, the
spread around this average result is remarkable and presumably due to the many
factors that affect the yields of crops.
Savings for nitrogen fertilizers
can be based on the area that is treated or on the
product that is harvested. The latter approach is probably preferable, because the
product is the objective. This leads to defining the efficiency of mineral N use,
e.g.
in kg of grain per kg of N applied.
