Agriculture Reference
In-Depth Information
100
90
80
70
60
50
regressions with confidence limits for P = 5%
5
10
15
20
25
30
mean mass diameter ( = mean weight diameter ) of soil particles in mm
Fig. 7.6
Soil clod size reduction and fi eld emergence (Heege and Vosshenrich
2000
)
mass diameter of soil clods from experiments in Germany. This parameter of soil
tilth is often denoted as mean weight diameter (MWD). It is determined by a sieving
process and by weighing the fractions.
The wide span from 3 to 20 mm mean diameter that can provide for a high emer-
gence may be surprising. Yet the balance between the water- and air supply in the
seedbed is important. In Germany, winter barley is sown substantially earlier in
autumn than winter wheat at a time, when the soil still is rather dry. Therefore, for a
good balance of water to air, winter barley needs a fi ner seedbed than winter wheat,
which gets enough water anyway because of the rather wet soil in late autumn or
early winter.
There are exceptions from the general rule that the fi eld emergence increases
with the soil break-up. These exceptions apply to soils with a high silt content in a
climate, where heavy showers instead of drizzling rains show up. Under these con-
ditions, the surface of a fi ne seedbed can get puddled by showers and in subsequent
dry weather it can become crusted. The result is a cut off in aeration and thus poor
emergence. However, these exceptions do not invalidate the general rule.
7.3.1
Sensing Soil Tilth
Since the soils in many fi elds are not uniform in texture or organic matter content and
compaction by the harvesting machines is irregular too, the tilth differs within a fi eld.
The knowledge that the farmer has about the site-specifi c clod sizes in the seedbed
depends on his visual impression and therefore is fragmental. There is a need for
real-time sensing of the site-specifi c clod sizes produced during seedbed preparation.
