Agriculture Reference
In-Depth Information
be obtained with a row spacing, which equals the mean seed distance within
rows. The theoretical optimum for bulk drilling would be a row spacing that
approaches zero, which is broadcasting (Heege 1967 , 1970 , 1993 ). Therefore, as
far as the spatial seed arrangement with bulk sowing is concerned, broadcasting
must be regarded as the best method. The problem is that not all sowing methods
for broadcasting provide for a sufficiently even depth control of the seeds. And
good depth control can be even more important than improvements in the seed
distribution over the area. Yet both objectives - precision in the seed distribution
over the area as well as an even depth - can be obtained by using wing-coulters.
The seeds are broadcast within the empty space below the wings and the flattened
soil underneath it.
Provided an adequate depth control is obtained, improvements in the seed
distribution over the area can under ceteris paribus conditions ( e.g. same seedrate
per ha or seed density) result in
small increases in emergence of seeds
less weed growth
small increases in yield.
An effect of improvements in the seed distribution over the area on the emergence
of seeds has been observed with closely spaced crops such as e.g. small grains
(Mülle 1979 ; Mülle and Heege 1981 ). This probably can be explained by wider
distances to nearest neighbouring seeds. For closely spaced crops, this reduces
competition for growth factors that promote emergence, e.g. water.
Less weed growth with improved plant distribution over the area is the result of
quicker canopy closing and hence faster shading of the soil.
The small increases in yield finally can be explained by a more even allocation
of several growth factors such as light, water, air and mineral nutrients to plants.
There is less light interception within the canopy, which promotes photosynthesis.
Yield responses of small grains, rape (colza) and beans to the seed distribution
over the area are shown in Fig. 8.5 . Similar responses to improvements in the seed
distribution over the area have been reported for maize and soybeans (Lambert
and Lowenberg-DeBoer 2003 ; Cox and Cherney 2011 ) as well as for cotton
(Reddy et al. 2009 ).
However, there are reasons why in practice any changes in seed spacing towards
more equidistant arrangements between neighbouring seeds irrespective of the
direction are realized rather slowly.
For bulk drilled crops with a high seed density such as e.g. small grains,
a decrease in opener spacing for drilling in narrower rows can present problems.
Especially on fields that were not ploughed, clogging of crop residues or clods
between adjacent openers can increase. This can impair the precision of the seeding
depth and hence the emergence (Heege 1993 ). Hence again in this respect too
both precise seed distribution over the area and accurate seeding depth must be
observed. Furthermore, the expenses for sowing machines increase. And finally,
with widely-spaced crops that are harvested by individual row units such as maize
and soybeans, the expenses for harvesting machines too are higher.
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