Agriculture Reference
In-Depth Information
seed-hopper
feed-roller
transmission,
continously variable
optical sensor,
counting seeds
computer
drive
opener
speed-sensor
Fig. 8.2
Closed loop control of the seed density of small grains by means of seed counting (Heege
and Feldhaus
2002
)
seed-density needed rises up only to an annual precipitation of 700-800 mm.
Beyond a precipitation of 1,000-1,100 mm it drops again. This may be due to the
fact that wet soils provide a higher emergence and thus might save seeds.
But as shown in Fig.
8.3
, the influence of
soil texture
is more distinct than the
effect of precipitation. Silty- or loamy soils always should be provided with higher
seed-densities than sandy- or clay soils. This too probably can be explained by the
fact that these soils supply plants more evenly during the growing season with water
than sandy- or clay soils do and therefore are better able to support a dense crop.
Site-specific control of the seed-density on the basis of the annual variation of
precipitation does not make sense, since knowledge about the supply of parts within
the field in rain-fed areas does not exist
a priori
. But data about the site-specific soil
electrical conductivity as a
substitute of texture
can rather easily be recorded,
Whether as an alternative also site-specific sensing of texture based on infrared
preferred, because practically these soil properties do not vary temporally, any maps
generated can be used for several decades as a basis for on-the-go control of seed-
density. Since fields with varying soil texture are common in many parts of the
world, a substantial gain in sowing precision could be obtained if differences in the
soil texture were taken care of in this way.
Crop plasticity
is often mentioned as an argument against a need for site-speciic
control of seed-density. This feature is based on the ability of individual plants of a
