Club of bologna proceedings

5. Straw effects in the seedbed 
Fi
g. 7
.
shows, how different methods of
cultivation and place
m
ent of chopped straw
affected the emergence of winter cereals in
Schleswig-Holstein. The straw placement
underneath the seed bed by plowing resulted in 
a 
field emergence of 80%. About the same
emergence was achieved using a rotary cultivator 
and placing the straw mainly on top of the
seedbed. Rotary culti vating wit hout a sieve and 
thus incorporating the straw mainly into the
seedbed, however, caused a decrease of the
emergence. 
Farmers often assume, that the low field
emergence associated with straw in the see dbed 
is the result of inaccurate seed placement by the 
openers. The general ex perience in fact is, that 

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49
the traditional openers do not function well in a 
seedbed with straw. Yet in all experiments with 
the rotary cultivator (see
Fig. 7
) a transverse 
broadcast sowing bar was used. This seeding
method provides for a rather uniform sow
i
ng-
depth even when straw is in the field [4]. And the 
good emergence with rotary cultivating and straw 
on the top of the seedbed prooves, that bad seed 
placement probably is not the reason. So why
did the straw in the seedbed impair the
germination? 
Several researchers have shown, that water
extracts from straw impede the germination of
seeds [5, 6, 7, 8, 9, 10]. Most of them a
s
sume, 
that products of the straw decompos
i
tion like 
organic acids or phenolic co
m
pounds are
responsible for the effect on ge
r
mination. 
Sometimes it is mentioned that the negative effect 
on germination especially 
o 
ccurs in anaerobic
conditions. 
We too looked at the effect of watery e xtracts of 
cereal straw on the germination of rape. Rape is 
the first winter crop sown in August in Sc
h
leswig-
Holstein and therefore especially affected by
straw. The watery e xtracts from wheat straw as 
well as barley straw and rye straw did reduce the 
emergence on fil
t
er paper [10]. Anaerobic or 
aerobic conditions were simulated by aera ting the 
extracts or not. The anaerobic con
di
tions were 
especially detrimental with wheat and rye straw, 
but not with barley straw.
But an important question still is, whether these 
watery extracts from straw act in the field in the 
same manner as they do in the laboratory
. 
All 
experiments which have been conducted about 
the effect of straw deco
m
position on germination 
in several countries were made with watery
extracts in the lab
o
ratory. But in what
concentration do the harmful compounds hit the 
seeds in the soil? This ce
r
tainly must depend on 
the varying rainfall. Since the time of Paracelsus it 
is known, that the concentration or the dose of a 
substance defines, whether it is harmful or vice 
versa even helpful. And further
m
ore, many soil