Agriculture Reference
In-Depth Information
1.2
1.0
0.8
0.6
sand
silt
loam
clay
Fig. 8.3
Factor for seed-density of winter-wheat depending on soil texture and precipitation for
flat fields and a mean annual temperature of 8 °C (From Wiesehoff
2005
, altered)
crop to act on inaccuracies in the local seed-rate as well as in the seed distribution
over the area by either compensatory- or
vice versa
restricted growth. Within limits,
the effect is such that the spatial growth of the plants automatically adjusts itself to
the space available. Especially with small grains, the plasticity of a crop can be
remarkable due to a matched development of lateral plant branches by tillering.
The result of a high crop plasticity is that the relation between seed-density and
yield presents itself as a rather flat curve. This means that the effect of a more pre-
cise seed-density on the
yield
is rather small. However, at the same time this implies
that more targeted sowing can result in substantial savings of
seed costs
. So the
benefit of site-specific seed-density control just shifts from yields to seed costs.
With crops that have a low plasticity -
e.g.
beans, sugar beets or potatoes - it is
vice
versa
(Fig.
8.4
)
Having in mind that besides crop plasticity the actual differences in soil texture
within fields will influence the benefits achieved from site-specific control of the
seed-density, it must be expected that results from field experiments will vary greatly.
Schneider and Wagner (
2005
) presented a survey of results based on experiments
with small cereals and maize from four different places in Germany. In all cases
there were benefits from site-specific sowing, partly in savings of seed costs, but
partly also from yield increases. The monetary value of these agronomic benefits -
site-specific control costs not subtracted - was between 13 and 92 Euros per ha. In
case an average agronomic monetary benefit of 50 Euros is assumed, it should
easily be possible to cover the site-specific control costs from this.
