Better Farming - November 2016

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Better Farming November 2016 FarmNews First > 47
CROPS: THELYNCH FILE
to reach the percentage. For example,
residue under nine holes out of 25
would be 36 per cent residue cover.
You can do such calculations
yourself in your fields.
The magic number for residue
cover is 30 per cent. At this level,
erosion is reduced to about one ton
per acre. Farmers and industry
representatives involved with soil
conservation agree this is an accept-
able level. I like to see about 40 per
cent residue in the fall. You will lose
some residue over the winter and
some will move with rain.
The reason you want to have crop
residue is to break the fall of rain
drops. Rain falls and hits the ground
at about 20 miles per hour. If rain hits
the soil it breaks the soil particles
apart. Once the small soil fragments
break away they move into the pores
in the soil that earthworms have
formed. The soil fragments plug these
holes. Then the water runs across the
soil surface and possibly even off the
field. Crop residue on top of the soil
breaks the force of the rain drop. It
also slows the movement of soil
across the field.
The results of our demonstrations
were interesting. First, growers were
pretty good at guessing what per cent
residue cover was left.
Secondly, the different conserva-
tion tillage tools left varying amounts
of residue, ranging from less than 15
per cent to about 40 per cent residue.
When the corn was combined, half of
the header had stalk choppers and the
other half was combined without
chopping stalks. In some cases when
the stalks were chopped with some
types of equipment, there was less
crop residue on top than if the stocks
were not chopped. But, with other
machines, the amount of residue was
greater.
When managing residue there are
a number of factors that affect the
amount of residue left on the soil. The
depth and speed of the tillage tool
affects the per cent of residue cover.