Managing Weed Seeds in Manure
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.
First of all, don’t assume that animal digestion will take care of the problem. Though it will reduce weed seed viability, simply feeding the material to livestock will not eliminate all seeds. Grass and soft-coated broadleaf weed seeds are more easily destroyed in digestion than hard-coated seeds. In a study conducted on rumen animals, such as cattle, 27% of hard-coated seeds remained viable after digestion. The gizzard digestive system of poultry is highly effective at destroying weed seeds, and only 3.5% of hard-coated seeds fed to ducks were recovered and found viable in a similar study.
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.
To learn more about the techniques for minimizing weed seeds, read this article on UNL Water by University of Minnesota Extension Educator Chryseis Modderman.