27
important tillage systems can be classified and
defined as follows:
Conventional tillage
- Generally refers to
mouldboard ploughing with soil inversion,
followed by a secondary tillage such as discing
and/or harrowing. Weed control can be
accomplished through cultivation or hebicides
use.
Minimum tillage
(reduced tillage) - Is similar to
conventional tillage, but with fewer trips and
shallower tillage depth. Implements are mainly
discs, chisels (disc planting, wheel
-
track
planting).
Mulch tillage
- Th
e
soil is disturbed prior to
planting. Tillage
implements such as chisels, field
cultivators, disc sweeps, or blades are used.
Weed control is accomplished by he
r
bicides
and/or cultivation. A mode of mulch tillage for
small grains is stubble
-
mulch [39] whe re winter
cereal stubble is left on the su
r
face of the soil
which is shallow mixed or surface cut without
inversion (implements for mixing: discs, chisel
-
ploughs, field cultivators, mulch treaders; for
non-i
nversion: sweeps, rotary rod weeders).
Ridge-furrow tillage
- The soil is left
undisturbed from harvest
to planting except for
nutrient injection and provides surface drai
n
age
[40]. Planting is in a seedbed set out in ridges
with sweeps, disc openers, coulters, or row
cleaners. Residues are left on the
s
urface
between the ridges. Weed control is by
herbicides and/or cultivation.
Chiselling
or
paraploughing
[11] - Consising
of subsoiling along the inter
-
row zone to loosen
the compacted subsoil.
Strip tillage
or
zonal tillage
- i.e. cultivation
along the inter-row zone only.
No-tillage
- Involves complete elimination of
mechanical seedbed preparation (except na
r
row
bands where the seed is placed) and rel
i
ance on
herbicides or cover
crops or both to control
weeds. In no
-
tillage the soil is left undisturbed
from harvest to planting, except for possible
nutrient injection. This system includes direct
seeding of small grains.
The last three tillage classes are known as
"conservation tillages"; the second one may or
may not qualify in this group depending on the
amount of residues left on the soil surface after
seeding [8].
No single tillage system is however superior to
any other and the most suitable system should be
sought for each pedoclimatic and general
agricultural condition.
Among the advantages of the so
-
called
conservation systems, supporters claim effective
soil
erosion control, water conservation and more
efficient water use, lower energy
r
equirements
(less use of fossil fuels), reduced labour
requirements, more timeliness of til
l
age
operations, so ensu
r
ing better flexibility with
regard to weather conditions and greater
possibility for double cropping in certain climates
(which means more intensive use of soils) and
less risk of environmental poll
u
tion.
These advantages can be obtained to diffe
r
ent
extents by one of the above
-
listed soil tillage
systems.
Drawbacks are also recognised, such as
increased energy costs for herbicides, fertilizer,
amendments and irr
i
gation; increased herbicide
use has a worse disadvantage: it contributes
towards dange rous environment pollution, which
ecologists are striving to oppose; on the other
hand di
f
ficulties are found in controlling some
weed species. In soils with poor internal drainage
(most clay soils) conservation tillage can
aggravate wetness
limitations in a tempe
r
ate
climate for both surface temperature and a
n
oxic
effects beneath.
The comparison of these systems in different
soils, in diverse climates and in more than one
year usually shows a very wide variation on the
yields and the trend over time has not yet be
e
n
clearly demonstrated in all cases; some long
-
term
modifications to soil traits are now appearing.
Very often different til
l
age systems give no
significant yield diffe rences in the long
-
term; in a
28
single year, however, some relevant differences
might occ
u
r, which only demonstrate the
existence of strong interactions with seasonal
meteorological events
for any given soil and
climate; these effects are usually compensated as
an average over many years. This is one of the
reasons for considering the debate s
t
ill open [12;
14]. When annual yield differences arise this
mostly depends on the effects on early crop
development; usually the reasons for these
differences are not clear or at most not clearly
demonstrated; e.g. it can be that excess water
drainage and consequently be tter root deepening
are the cause [28].
According to most authors [7; 12; 14; 8] the
conditions for which, at least on average, each of
the tillage systems seems advisable can be
identified in the following way:
°
conventional mouldboard plou ghing fo
l
lowed
by secondary tillage
operations still seems the
best solution for soils where internal drainage
is a problem, such as clay soils with poor
structure, and for most crops, but especially
for sugarbeet, carrots and similar crops (
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