Club of bologna proceedings

3. Weed control 
It is commonly known that the moldboard plow 
is the most effective tool for 
m
echanical weed 
control in humid areas. Yet on the other hand it is 
a very energy
-
plus labor consuming tool. And 
the bare soil surface left by the plow induces ero
-
sion. This applies especially to sloped fields with 
silty soils and continental climate. 
T
he steady
advances in chemical weed control induce the 
farmers more and more to rely on herbi
c
ides 
instead of the plow. From an environmental point 
of view the herbicides as well as the plow can be 
questioned. Yet the future looks brighter for
weed control by herbicides than for weed control 
by the plow. The advances which are in progress 
for efficient and environmentally safe herbicides 
as well as for crops made r
e
sistant to herbicides 
by genetic engineering are remarkable. It will
hardly be possible to o
f
fset these ad vances by 
better plows. 
4. Crop residue management 
The less cultivation occurs, the more the crop 
residues can hamper the establishment of the next 
crop. This applies especially when crops follow 
one after another within a short time period
as 
e.g. with a rotation winter rape
-
winter wheat - 
winter barley, which is very common in
Schleswig-Holstein. If plowing is omitted, straw 
not needed for bedding or other pur
p
ose, and 
straw burning in the field is prohibited, the farmer 
needs a method 
f
or coping with straw near the 
seeds. Cutting through the straw by heavy disk 
openers for direc
t-
drilling sometimes is possible 
in dry regions, when the soil is rather hard and 
the straw is brittle. In humid areas this method 
often fails, since the soil as well as the straw here 
are more flexi ble. Therefore the straw is not cut 
by the disk
-
openers, but pushed into the furrow. 
The result very often is a low field eme rgence. 
The situation is different with widely spaced crop 
such as sugar beets, maize and so
y
beans. The 
wider ro
w-
spacings allow using residue clearing 
attachments to the seeders, which move the
straw to the inter
-
row area. In spring,
furthermore, not much straw is left. And residues 
of some catch
-
crops are easily cut by disk
-
openers even in humid regions. 
Straw on or near the soil surface is very e
f
fective 
in reducing erosion. There have been attempts to 
place it on the surface immed
i
ately after sowing 
(
Fig. 6
). Our concept for this has been a rotary
-
cultivator with a tran
s
verse bar for broadcast
-
sowing and sieves, onto which the soil
-
straw 
mixture is thrown. The soil particles pass the
sieve openings and thus get directly onto the
seeds, whereas most straw particles do not pass 
and thus are placed onto the surface. A rotating 
drum-sieve as well a
s
a chain
-
sieve were used. 
The chain
-
sieve separated more effectively and 
therefore the results presented later refer to it.
In case the preceding grain crop was ha
r
vested 
by stripping, the standing straw left can also be 
placed on top of the seed bed by flailing it aside. 
This method has been used at the Uni versity of 
Giessen [3].