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Mustard Harvesting
By Bill Greuel, Provincial Specialist - Oilseeds
and Transgenic Crops, Saskatchewan Agriculture, Food and Rural
Revitalization
I'm an optimist - I wrote this article in May.
That assumes a lot of things, including a successful growing season
and a current focus on harvest and crop quality. I hope that is
the case. The care you take in harvesting can affect quality which,
in some cases can be as important as yield when considering net
return.
Swathing versus Straight
Combining
Arguably, straight combining can lead to higher quality mustard
than swathing. However, based on the situation and considering
mustard type, evenness and stage of maturity and crop height,
you may still need to swath. Yellow is the most shatter-resistant
of all mustard types. Beyond that, the most shatter-resistant
types are oriental mustard, brown mustard, Polish canola and Argentine
canola (in declining order). I added canola as a reference point:
Argentine canola has very little shatter-resistance and is generally
swathed.
Evenness refers
to the relative range of maturity between plants. In many fields
high growth areas in low-lying spots, may mature later than other
areas. With swathing, you can force consistent ripening. If you
have uneven maturity and delay until all plants are mature enough
to straight combine, you run the risk of increased shattering.
At the same time, straight combining too early will increase green
seed numbers and elevate moisture content.
You also need to consider the stage of maturity
because you are better off straight combining over-ripe mustard
because swathing can cause shattering. Maturity can change very
quickly in hot dry conditions and you need to monitor your crop
very closely as it nears harvest.
Also, consider crop height when swathing to
ensure that the cut is made high enough to adequately anchor the
windrow in the remaining stubble, but not so low that the pick-up
reel gathers stones and soil.
Time of Swathing
When to begin is the most important decision related to swathing
mustard. Timing can affect yield, quality and net return. For
all mustard types, swathing should begin when the majority of
seeds are at 25 per cent moisture. At this point, seeds will feel
firm when pressed between the thumb and forefinger. Some pods
will have developed a purple tinge; lower pods will have changed
colour but the upper pods will remain green. Break open several
pods along the main stem of the plant. For oriental mustard, 75
per cent of the seeds will have some yellow colour; for brown
mustard, 60 per cent of the seeds will have some reddish-brown
colour. Be sure to crack the pods and look at the seed inside;
do not decide when to swath solely based on pod colour change.
Varieties mature differently, in some, the pod will change colour
before the seeds. In others, the reverse occurs.
When swathing, cut just below the level of the
lowest pods. In most cases, this should leave ample stubble in
which to anchor the windrow. This is crucial to prevent the swath
from blowing. This may require rolling and packing the windrow
into the remaining stubble. Set the roller so that the windrow
is firmly packed, but take care not to shatter overripe pods or
pack the windrow so tightly that it cannot dry properly.
If the green seed count is unacceptable at harvest,
the only thing that will lower it is time in the swath. In order
to reduce green seed, the moisture content in the crop must be
above 20 per cent and the ambient temperature must be above 5†C.
Extreme heat shortly after swathing, or a frost just before or
even a few days after swathing, can lock in the green colour.
Green seed will not clear out in the bin.
Straight combining
You can straight combine mustard that is uniformly mature and
has a low green seed count. Also consider straight combining if
the crop is too short to properly anchor the windrow. Set the
reel speed approximately the same as the ground speed. This will
help prevent shattering. The cutter height should be just below
the lowest pods in order to minimize the amount of stem fed through
the combine.
Remember long-term safe storage requires a moisture
content of less than nine per cent. The moisture level of mustard
generally increases by one per cent after binning.
Combining
Combine mustard when the moisture content has dropped to around
nine per cent, and when most seeds are mature and have an acceptable
green seed count. After harvest, green seeds will not significantly
cure.
Depending on crop conditions, cylinder speed
should be about one-half to two-thirds of that used for cereals.
Reduce the cylinder speed to between 400 and 800 rpm, or to the
point where the amount of cracked seeds is acceptable. Over-threshing
at the cylinder and concave is a common problem when harvesting
mustard, causing cracked seeds, high dockage and loading of the
shoe with excessive amounts of broken stems and pods. Set the
concave clearance to give as good threshing as possible. This
will keep the number of unthreshed and broken stems and pods to
a minimum. Concave clearance should be wider at the front, up
to 25 mm (1 in) and narrower, 3mm to 13 mm (1/8 - 1/2 in) at the
back.
Compared to cereals, the cleaning action for
mustard depends more on shaking separation than on wind separation.
Set the fan speed to approximately three-quarters of that used
for wheat. Air volume should be just enough to keep material moving
evenly across the sieves. Increase the speed of the shaker shoe
by an additional 10 per cent if possible.
The top sieve, or chaffer, setting should be
6 mm to 10 mm (1/4 - 1/3 in) and the lower sieve setting 3 mm
to 6 mm (1/8 - 1/4 in). Excessive trash in the hopper means the
sieves are open too much. Alternately, if the sample is perfectly
clean, open the sieves slightly. If the returns are too high,
there may not be enough wind, the top sieve may be open too much
or the cylinder and concave may be over-threshing.
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