Club of bologna proceedings

2. Soil size reduction 
Exept for sandy soils usually some size r
e
duction 
of soil par
t
icles by secondary cult
i
vation is
needed for a high field emergence.
Figure 3
shows the emergence of small cer
e
als depending 
on the mean mass diameter of soil particles.
Surprising is the wide span from 3 to 20 mm
mean diameter, which can provide for a high
emergence. Yet here too the balance between
the wa
t
er - and air su pply in the seedbed is 
important. In Germany winter barley is sown
substantially earlier in autumn than win
t
er wheat 
at a time, when the soil still is rather dry. For a 
good water to air balance therefore winter barley 
needs a finer seedbed than winter
-
wheat, which 
gets enough water anyway be cause of the rather 
wet soil in late autumn. But here again re
l
iable 
weather forecasts for a longer time would be
helpful. 
For soils with a high silt content a fine su rface can 
get puddled by rain, can form a crust on
subsequent dry days and thus pr
e
vent the
seedings from emerging. In order to prevent this 
crusting the soil surface should not be fine, but at 

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47
least contain some coarse particles. Yet the
seeds still should be in contact with fine soil for a 
high germinatio
n
rate. Therefore under these
conditions a se gregation of particle sizes within 
the seedbed during cultivation can help. As
shown in 
Figure 4
this segregation can occur if 
slow moving drawn tines are used. When the 
secondary cultivation was performed by 
t
he 
much faster moving tines of p.t.o. driven
implements, no segregation did show up.
Probably this can be explained by the time which 
is needed for the small particles to sift
downwards in the voids behind the tines. With 
fast moving tines, this time is to
o
short for a 
remarkable segregation to take place.
Whether soil surface crusting occurs too d
e
pends 
very much on the weather. Most areas of
Western Europe have a rather mar
it
ime climate, 
where the drizzling rain only seldom causes
crusting of silty soil
.
In regions with continental 
climate the situation is quite di
f
ferent. Here the 
rain comes down in short, but heavy showers, 
which promotes surface puddling. This too might 
explain, why p.t.o. driven cultivation is more
common in Wes
t
ern Europe than in ar
e
as with 
continental climate. 
The climate or weather can substantially help to 
promote soil breakup for size reduction on heavy 
soils with a high clay con
t
ent. The 
s 
equence 
freezing-thawing or alternatively the se
q
uence 
wetting-drying can reduce the stre
n
gth of soil
clods with clay substantially. A prerequisite for 
this effect in most cases is a well aerated loose 
soil, thus a primary cultivated soil.