Agriculture Reference
In-Depth Information
Table 1
Expected potential values of soil and cropping system quality indicators influenced by
soil tillage in different environments
SOM = soil organic matter, + + very high, + high, - low, - - very low.
Enironment
Indicator
Tropical,
humid
Temperate,
warm
Temperate,
cold
Semi-arid,
warm
Semi-arid,
cold
Cropping system
diversification
A
+ +
+
+
- -
- -
SOM mineralisation
+ +
+
-
+
- -
Organic matter
(biomass) production
+ +
-
+
- -
- -
N volatilisation
+ +
+
+
-
-
Soil compaction
+
+
-
+
+
Soil tilth
-
-
+
-
-
Soil erosion
+ +
+
-
+
+
Soil water retention
-
-
+
- -
- -
Soil nutrient uptake
+ +
+
-
-
- -
Nitrate leaching
+
-
+ +
- -
-
Pests, diseases and
weeds
+ +
+
+ +
-
-
A
Includes the possibility to grow cover crops and intercrops.
rates, had a more pronounced effect on soil mechanical characteristics than tillage
per
se
(Munkholm
et
al
. 2001a). For example, cropping systems with higher organic matter input
showed more desirable aggregate strength and soil fragmentation features, while systems with
lower organic matter input showed increased cementation of dispersed clay with increased soil
dryness, leading to higher aggregate tensile strength (Munkholm 2002, Munkholm
et
al
.
2002). All these effects, however, were highly dependent on soil water content (Munkholm and
Kay 2002).
In the Netherlands, Kouwenhoven
et
al
. (2002) tested an 'ecoplough', developed to meet
organic system requirements of relatively shallow ploughing with good soil inversion for weed
control, on Luvisols. This plough has seven or eight bottoms for ploughing depths of 0.12-0.20
m, a working width of 2.1 m and a working speed of 1.7 m s
-1
, and can be coupled with a
tractor equipped with low-pressure tyres. The 'ecoplough' produced a rather smooth soil
surface with relatively fine, strong, stable and moist aggregates. Organic matter, soil biota and
nutrients were concentrated higher in the soil profile, which positively inf luenced soil worka-
bility and crop growth. Crop yields were similar to those after conventional ploughing, but
weed populations (especially perennials) increased when ploughing depth was <0.2 m.
Most of these findings demonstrate that the abstraction of the tillage effect out of a cropping
system context can lead to misleading conclusions. Furthermore, this 'reductionist' approach is
highly questionable in organic farming, where agricultural management should always be
systems based (Ikerd 1993). In general, it would always be desirable to first plan an organic crop
rotation well suited to the local context and subsequently to tailor tillage choice and manage-
ment to such a rotation (Wijnands 1999). Where some reduction in tillage frequency is desira-
ble, inclusion of a no-till ley phase in the rotation should be considered (Olesen
et
al
. 1999).
The relative importance of the pros and cons of tillage in a given environment should
always be carefully considered before planning the crop rotation, based on the expected value
of relevant soil and cropping system quality indicators (Table 1).
