Manure is a valuable resource for farmers to use to build and enrich their soils. It adds nutrients and organic matter to soils for growing corn and other crops. However with the benefits gained there is a concern that producers need to remember when utilizing this fertilizer resource.
Weed seeds can be spread across the farm or to neighboring farms if they are present in the manure. This can be especially of concern if they are spreading hard to control weeds such as Canada thistle or leafy spurge.
Most forages and feeds are clean of weed seeds. This is due to modern weed control practices producers are using today. However there is a chance that some sources of manure may have weed seed contamination present. Factors that affect the potential for this can include feed sources, types of animals that are consuming it, and the type of feed and\or manure handling systems being used.
The level of contamination from various feed sources often depends on the package it is feed in after harvest. Most silages and pelleted feeds have very little viable weed seed left after fermentation or processing. In addition, the type of weed seed in feed will determine its viability in the manure. Weeds with soft seed coats don’t survive digestion by livestock. These species include foxtails and other grass species, sweet clover and pepperweed. Weeds with harder seed coats such as common lambsquarter and pigweed, will not break down and will pass through the animals digestive tract in tact at a much higher percentage.
The type of animal being feed will also impact weed seed viability. Studies have shown chickens will destroy 98% of weed seed they consume due to the grinding action in their gizzards. Research has also found about 75 % of the seeds are broke down when feed to hogs and cattle and 90% of the seeds were destroyed when feed to horses and sheep.
The biggest contribution of weed seed comes from contaminated hay and grain used as a feed source. A portion of the seed can remain viable after it has been feed and passed out of the animal. The problem producer’s face with this is that it is difficult to accurately assess how much seed is still viable when it goes on the targeted area. Remember that one velvetleaf plant seeding out in a corn or soybean field produces 800 or more seeds so it is critical to recognize any potential for problems and manage accordingly.
If producers want to prevent the spread of weeds on their property it critical to know the source of your manure and\or not purchase or feed weed contaminated feeds or forages.
Producers may want to use some techniques such as composting manure to reduce weed seed viability. Storing manure for three months has been sown to decrease weed seed viability by 60 % or more. Composted manure will reduce seed viability through high temperatures and chemical reaction. It is critical to turn the pile regularly to promote even heating and expose all the weed seed to the heat.