Other notable results were that seed from two summer weeds, silverleaf nightshade and prairie ground cherry also survived the digestion process with little loss in viability.
Livestock could graze on mature berries in the field and potentially spread these weeds.
They also found viability of seeds from most species was also reduced in the rumen after 48 hours, though the effect was less than ensiling.
From the March 2012 edition of Agriculture Today.
He and silage expert and NSW Department of Primary Industries livestock research officer John Piltz conducted their research through the EH Graham Centre.
It is not yet fully understood what aspects of silage are critical for killing weed seeds.
The fate of weed seeds incorporated in silage has been investigated.
Remember, even if the feed was ensiled and the manure was composted before spreading, it’s still possible for weed seeds to remain viable. A 98% reduction in viability seems sufficient, but even low seed survival rates can be problematic. A 2% survival of 75,000 seeds would leave 1,500 viable seeds remaining per ton. Applied at 8 tons per acre, that would increase the weed seedbank by 12,000 seeds per acre! Therefore, it is crucial to scout fields that receive manure to head off any severe weed infestation.
Temperature and moisture are the two most crucial elements for seed mortality in compost. Studies have shown that sustaining the compost at that benchmark of 140⁰F for three days can reduce weed seed viability 90-98%, so long as a minimum of 35% moisture is maintained. Another study found that overall duration was important and that it took between 21 and 50 days of composting for best results.
So what can you do to reduce weed seed viability beyond the gut? In general, heat is the enemy of weed seed survival. The benchmark for good seed mortality is 140⁰F (60⁰C) sustained for three days. Hot temperatures that fall below that mark or a shorter duration will still kill some weed seeds, but not as thoroughly. How you subject the weed seeds to heat is up to you, but below are a few suggestions.
Minimize weed seeds in manure by composting
What if ensiling isn’t feasible? What if your manure is already contaminated with weed seeds? In those cases, composting is a very effective method for killing weed seeds – more effective than ensiling.
Internal heat generated by properly composting manure will kill most weed seeds – even the hard-seeded weeds. The key word here is “properly.” Aged manure is not composted manure. I’ll say it again: aged manure is not composted manure. Proper composting requires active management and must be monitored and aerated for correct weed-killing conditions to develop.
Small but mighty, weed seeds in manure can be problematic when they result in overgrown, weedy fields after manure application. A survey found that fresh manure on dairy farms had an average of 75,000 seeds per ton. But, luckily, there are some measures that can be taken to reduce the viability of those weed seeds.
Even under the most diligent composting program, there can be seeds that survive. It is theorized that since manure is not a uniform product, this mortality escape is due to cooler pockets that do not sustain high temperatures for long enough. Therefore, just because manure has been composted does not necessarily mean it is weed seed free.