On one hand, research has shown over and again
that weed seeds are practically nil in poultry litter.
Sullivan has a collection of research papers that proves
One paper showed that poultry litter will enhance
the germination and growth of weeds in pots inoculated
with weed seeds, whereas pots that were not inoculated
with weed seeds did not grow any weeds because the
poultry litter itself did not contain any weed seeds.
Such data suggests a simple fertlizer effect.
However, in the description provided by Sullivan below,
weeds pop up in pastures quite prominently after
poultry litter fertilization. This is in direct contrast to
strips that were fertilized with synthetic nitrogen where no
weeds beyond normal can be found.
This suggests an organic reaction, possibly due
to humic substances or some other biostimulant
released by the poultry litter...that reaches deep
down into the pasture ecosystem and causes dormant
weed seeds to germinate.
Further practioner-based collaboration can be learned
from the Luebkes of Austria, who found that bio-mature
compost does not promote weed seed germination, and thus
good compost is actually a benefit to the grower from
the weed control angle as well as soil tilth and fertility
angle. Whereas, in their field trials, immature manure-based
composts stimulated weeds to germinate. Again, suggesting a
feedback loop where weeds of "disturbed" sites and immature soil
conditions take a cue to grow.
On the other hand, spiny pigweed is one of the more
common stupid, darn, hard-to-keep-out-of-your-garden weeds
when raw manures are used.
This raises the question as to whether the poultry litter
was in fact clean of spiny pigweed seed; even though the data
suggests otherwise, it puts a doubt in your mind.
And leaves the farmer guessing till another day.
> Here is a hypothetical experiment. If we apply 3 tons
> of broiler litter per acre and the same equivalent
> of nitrogen fertilizer to plots of bermuda grass
> we will see more weeds in the littered plots
> than we see under commercial fertilizer plots
> 6 weeks following the application. Why?
> I've heard a number of farmers say chicken litter
> brings on the weeds in pastures. I have observed
> the same myself. Just this summer I saw a bermuda
> pastured littered at a 3-ton rate which had abundant
> spiny amaranth (not a traditional pasture weed).
> Another bermuda pasture which had 300 pounds of
> 17-17-17 and there was no spiny amaranth. In a
> garden located in the same pasture where the
> commercial fertilizer was applied, there were
> mega spiny amaranth plants growing in sweet
> corn under conventional tillage. Why?