Club of bologna proceedings

4. Overall effects of tillage 
It would be quite a hard and too ambitious task 
to summarise all the previousl
y-
mentioned effects 
and interactions and d educe a set of rules from 
them for practical application.
Let us therefore recall the evolution of some
attitudes towards tillage problems in the past. For 
many thousands of years, starting from crude
wooden tillage implements up to the Roman
plough, the soil was cut and irreg ularly mixed to a 
shallow depth (15
-
20 cm).
In many
Mediterranean areas with extensive agriculture
this Roman type plough was used up until a few 
decades ago and it is still used now in some less 
developed forms of agr
i
culture; its ploughing
depth was shallow, the plane of separation of
tilled and untilled la yers irregular, and burying of 
surface residues incomplete. In the VII century a 
rough inverting plough was first proposed in
Bavaria but only in 1796 Jefferson developed a 
formula for the mouldboard plough and Ne wbold 
patented a cast iron ploug h, made available in the 
1830's and studied in Italy by Lambruschini and 
Ridolfi. A number of years later it came to be 
accepted by farmers [4; 3]. 
Within the last century technological
develop-
ments, available hig
h-
power tractors and 
initially low fuel cos
t
s encouraged the dee pening 
of soil tillage and comparisons among the
performances of different tillage impl
e
ments. 
Many decades ago most tillage e xperiments dealt 
only with particular aspects of this technique,
usually within the framwork of a traditiona
l
tillage system. These aspects were depth of
tillage, type of impl
e
ments, time of tillage
operations, crop sui
t
ability of certain tillage
programmes, alte rnation of tillage (especially
depth) over the years. The role of deep tillage 
has been e mphasized f or about two centuries; 
agronomists used to discuss the plants' need for 
space in depth [15; 17]. Most of these
experiments were based on short-term trials only. 
Some referred to initial soil break til
l
age of
pastures or deforested soils, and had a special
meaning. 
Fig. 17
shows typical 
r
sults on yields 
after ploughing at different depth, breaking
previously uncultivated land; it is interesting to 

---

26
note the quite different and still reasonable
response of these cases. 
When trials were performed on arable la
n
d for a 
number of years, approximately a
p
proaching a 
steady state condition [16; 33; 34; 35; 36], the 
results [14], show that on wheat, no
-
tillage (zero 
depth) or strip
-
tillage (rot
o-
tilled only 5
-1
0 cm 
deep) usually give lower yields interpreted as a 
consequence of poor drainage in wet years while 
they usually perform better in dry years. Wheat 
does not seem to gain advantage from tillage
deeper than 25 cm (its yield increases at most 15 
kg
.
ha
-1
.c
m
-1
around this depth). It seems
essentially important to
e
nsure good planting
conditions only [37]. In several northern
countries reduced tillage and direct drilling have 
been found as suitable as mouldboard ploughing 
for establishing autumn sown crops [25]. 
For maize (main crop), no
-
tillage and mi
ni
mum 
tillage give mostly lower yields (-3 to -40%), with 
uncertain advantage at depths of more than 25
-30
cm except where drainage is a problem.
Maize as 
seco
nd crop (after wheat) on the contrary 
often achieves better results than with traditional 
deep tillage; this can be
interpreted as due to 
timeliness of planting. One could question
whether the yield advantage is exactly that
expected for early planting, since at this time of 
year the loss of yield for a 1 day delay in planting 
is of the same order of magnitude. Sugarbe
e
t 
usually gives lower yields with no
-
tillage and only 
when the soil structure is very good can the depth 
be reduced to 25
-
30 cm. Similar results are
expected from carrots and swedes [15; 25]. 
The different response to tillage depth of crops in 
rotation im plies a rotation in tillage depth too. 
This is not necessarily a passive consequence of 
crop sequence, since some direct favourable
effects of tillage depth
al
ternation have been
demonstrated in some cases 
(
Fig. 18
) and 
was intuitively assumed by authors in the past 
[15; 16; 17]. 
The use of chisel instead of mouldboard
ploughing has given inconsistent results. Usually 
the results from chisel on the soil are expected to 
be better than for ploughing when the soil is
somewhat drier, therefore in a dry summer; 
i
n 
any case it leaves most plant residues on the soil 
surface, which is not always appreciated on flat 
land. The po
s
sibility of double tillage (ripper
followed by shallow ploughing) seemed a
solution, but the experimental results are rather 
inconsistent and farmers seem not much attracted 
to this technique. 
As a whole, after a long world
-
wide series of 
experiments and experience in the last few
decades it is now clear that the mythical
mouldboard plough can no longer be consi dered 
the unique basic implement for all soil cultivation; 
it should only be used for agr onomic reasons and 
not just blindly following tradition. The main
reasons for using the mouldboard plough remain: 
to remove plant cover and residues from the soil 
surface, to bury these and other org anic materials 
(farm manure) in order to promote their
degradation to humus and minerals, to expose 
surface clods to weathering, to establish (after 
secondary operations) a suitable seed bed.
Compaction as ploughpan and from tractor
wheels caused by the ne ed for at least two 
trips 
for seed bed preparation are the main
drawbacks.