Agriculture Reference
In-Depth Information
segregation. This is, because these tines tend to lift more coarse clods to the surface
and hence to create larger voids for the small particles to sift downwards in.
Many secondary cultivation implements have tools that operate with rather low
speeds. Examples for these tools - in addition to drawn cultivator tines - are drawn
discs and rollers or power-take-off driven rod weeders (Fig.
7.12
). These tools hence
can leave a partially fractionated seedbed (Winkelblech and Johnson
1964
; Maze
and Redel
2006
).
Recording the fractionation of the seedbed may be possible on the basis of the
soil resistance or of the impact forces exerted on horizontal sensing tips that are
mounted at suitable depths of a vertical tine (Adamchuk et al.
2008
). As with sens-
ing of the general soil break-up (Fig.
7.7
), the best results probably will be obtained
by using the standard deviations of the impact forces (Figs.
7.9
and
7.10
). Clods on
top of a fractionated seedbed can be expected to deliver higher standard deviations
than the fi ne particles in the zone provided for seed placement.
Yet the problem is not the sensing method. It is the lack of cultivation tools,
which allow for precisely adjusting the
intensity of fractionation
. The develop-
ment of cultivation tools suitable for such an adjustment is an important prerequisite
for more precision in the vertical direction of the seedbed. There is an urgent need
for advances in this direction.
7.4
Stubble- and Fallow Cultivation
Stubble- and fallow cultivations are “interim” operations between two successive
crops. When a crop is sown a few days after harvesting of the preceding crop, they
may be left out completely. Often planting occurs some weeks or a few months after
harvesting. Then only one operation may be necessary, which after small grains is
called stubble cultivation. But when a complete fallow year (summer-fallow) is prac-
tised before another crop is established, several passes of fallow cultivation may be
needed. So the length of the fallow period after harvesting is an important criterion.
Generally, humid, high yielding areas have short fallow periods, since the
water supply for the crops hardly is a problem. In dry-land regions the situation
can be
vice versa
. Here there may be plenty of land, but not enough water.
Therefore, a long fallow time can be reasonable in order to accumulate and store
precipitation in the soil, which then later can be useful to get a better crop yield.
The rationale of summer-fallow is to use the precipitation of 2 years for a crop
growing season of 1 year.
The objectives of stubble- or fallow cultivation are
weed control
, residue man-
agement
, sometimes
erosion control
and
conservation of soil moisture
.
Weed control
as an objective of cultivation has lost in importance as a result of
modern possibilities with effi cient herbicides (chemical fallow), which can easily be
realized in a site-specifi c mode (see Sect.
6.2
)
.
The objectives in
residue management
depend on the climate. In humid, high
yielding areas with short fallow periods, the main objective is to get fast decomposition
