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| Residues are what is left in the field after a crop is
harvested.
Some farmers still call it, "trash", but that leaves the wrong
impression.
Trash is something we do not want to see, we want to dispose.
Residues
are something to manage. They have several positive benefits, and
some challenges. |
The benefits include: limiting soil detachment by wind and
water (the
first step in erosion); slowing water movement on the soil surface,
thus
decreasing runoff velocity and increasing infiltration into the soil
which
decreases runoff volume and amount of soil transported; and conserving
soil water by decreasing evaporation from the soil surface.
The challenges are related to pest management. Residues in the field provide shelter for insects to spend the winter. Dormant stages of pathogens may inhabit residues. If weed control is not adequate, weed populations may increase in residue, and the weeds may harbor insects and diseases over the winter. |
| The wheat field in the picture at right has about 85% residue
cover,
measured by the transect method (described below). These pictures
were taken on dryland fields at the USDA-ARS Conservation and
Production
Research Laboratory at Bushland, TX on April 5, 2001. The wheat
was
harvested in June, 2000. (Larger picture) |
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The sorghum field at left had about 50% residue cover.
The sorghum
was harvested in October, 2000. (Larger picture) |
| The soybean field at right has about 33% residue cover.
Closer
examination reveals that 2/3 of that residue cover was sorghum stalks
from
the previous crop year. (Sorghum stalks were in the field about 18 to
20
months after harvest when the picture was taken.) The soybeans
were
harvested in October, 2000. The sorghum was harvested in October,
1999. (Larger picture) |
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The cotton field at left has about 15% residue cover.
Cotton
was harvested in November, 2000. (Larger picture) |
| The line transect method estimates the residue cover using a
tape,
or a rope with knots at intervals along the rope. The line is
stretched
on a 45o angle to the row direction. Typically, the
rope
would have 100 knots in it, or a 100 foot or 100 meter measuring tape
could
be used.
In the picture at right, a 6" interval was used from 0 to 50
feet.
A count was taken if residue was under any foot or half-foot mark on
the
tape. In this picture, there is no residue under the 6" mark, but
there is residue under the 12" mark. In this picture, the residue
cover is 50%. This is done for the length of the tape.
Since
100 points were observed, the count is the per cent cover. |
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These students were determining residue coverage on the plots
shown
above as part of their lab requirement in a soil and water conservation
class. Several counts were taken on each field, and the results
averaged
to determine the residue cover. (Larger picture) |
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