Agriculture Reference
In-Depth Information
of the large amounts of residues in order to avoid interference with seed openers.
The decomposition of the residues depends on its contact with the soil, therefore on
its incorporation by cultivation. A rule for small cereals in Germany is a depth of
incorporation or a soil layer of 1-2 cm per every 10 dt of straw per ha (Taeger-Farny
2003
). Since high yielding small cereals can leave about 90 dt of straw per ha, this
would mean a depth between 9 and 18 cm.
The grain yield within a fi eld can vary considerably, and the same holds true for
the residues. Consequently, the depth of incorporation should not be uniform,
instead it should be adapted to the site-specifi c amount of residues. Pforte and
Hensel (
2006
) as well as (
2010
) propose a control system for the
depth of incorpo-
ration
that is based on percent residue cover. Their online approach relies on vehi-
cle based refl ectance spectroscopy and wavelengths in the near-infrared range from
about 800 to 1,400 nm. Within the visible- and infrared spectrum, this is the wave-
length range that has the maximum difference in refl ectance between straw on the
one side and bare soil on the other side. This means that this near-infrared range can
provide signals for an online on-the-go control of the incorporation-depth based on
percent residue cover.
A varying site-specifi c residue load can also result from an uneven straw distri-
bution by combines. This applies especially to high capacity combines with wide
cutter heads. However, an even distribution and short chopping of the straw are
technically possible and can hopefully be taken for granted in the future. It would
not be reasonable to adjust the depth of straw incorporation to defi ciencies of com-
bines that can be corrected.
It might be possible to sense the site-specifi c residue load in other ways, namely
either by converting from site-specifi c crop yields to amounts of residues or by
remote sensing from satellites (Zheng et al.
2012
). However, none of these methods
has been fi eld-tested for site-specifi c operations.
The objectives of residue management are quite different in regions with dry-
land farming and long fallow periods. Here fast decomposition is not a topic; it
might be even a disadvantage. Instead, the prevention of soil erosion - mainly via
wind - is a much more important point (Schillinger and Papendick
2008
).
Residues left on or near the soil surface are very effective in reducing erosion by
wind as well as by water. Therefore, when summer-fallowing of erosion prone
soils is practiced, incorporation of the residues should be mostly avoided. The
objective is having at least partly “
anchored crop residues
” on the fi eld. These
residues extend well above the soil surface, yet still are attached to the soil,
e.g
.
by their roots.
Conservation of soil moisture
as an objective of stubble- or fallow cultivation
too is highly dependent on the respective climate. In a humid climate this objective
hardly counts. Yet in dry-land regions, success in farming strongly depends on the
ability to manage water.
How should in this respect fallow fi elds be managed? The important point here
is to minimize evaporation by weeds as well as from bare soil. Based on the same
area, plants always evaporate more than bare soil. The rationale of summer-fallowing
rests on this. Plants with their elaborate root system just are very effective in
