Agriculture Reference
In-Depth Information
hydraulic cylinder
seed hopper
direction of travel
seeding depth
control unit
outer square tube
inner square tube
gauge-
wheel
original soil surface
drying front
disc-opener
lowered soil surface
seed depth
drying front sensor
v-wing scrape r
Fig. 8.9 Schematic of experimental precision seeding unit with depth control based on the posi-
tion of the drying front combined with a reduced seed cover. The final press wheel for closing the
seed furrow is not shown. Details are no to scale (From Bowers et al. 2006 , simplified and altered)
In regions with continental climate , the rain is less frequent, but instead when it
occurs, it is heavier. And the periods without rain are longer. As a consequence, here
the concept of rising moisture with increasing depth is more reliable. Hence prob-
ably it is not incidentally that the concept of “moisture seeking” started in regions
with continental climate.
In areas where long dry spells frequently occur, the difference between germina-
tion on the one hand and emergence in the field on the other hand can get important.
Seeds placed into a moist soil zone that is rather deep below the soil surface might
germinate, but not generate an emerged seedling because of a long distance to the
soil surface. Under these circumstances, seeding to moisture alone is not sufficient.
It must be supplemented by seeding close enough to the surface. This obvious con-
flict of objectives can be sorted out by scraping aside some soil from the top along
the seed row and thus creating a lower soil surface for emergence.
Figure 8.9 shows how - based on sensing of the drying front in a field - on
the one hand seeding into moist soil and on the other hand a lowered soil surface
for safe emergence can be obtained. The drying front within the vertical soil
profile is where the water evaporates. Therefore, it is just beneath the top layer of
dry soil, in which the water content is in balance with the relative humidity of the
air. The vertical position of the drying front is sensed via the electrical resistance
or voltage that exists between an insulated electrode at the tip of the drying front
sensor (Fig. 8.9 ) and the seeding unit. Locating the drying front then allows to set
the scraper in such a way that the air dry soil and in addition a thin layer of sub-
jacent moist soil are swept into the inter-row area. The seeds thus are put into
moist soil.
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