Nitrogen costs are high, and growers are looking hard at manure as an alternative source of nitrogen.

However, a study published in the latest edition of Agricultural & Environmental Letters, the journal of the American Society of Agronomy, the Soil Science Society of America, and the Crop Science Society of America found that palmer amaranth can pass its seeds via contaminated manure.

The transmission of palmer amaranth via manure (frequently ingested via contaminated feed) has been previously reported, researchers wrote. However, past research has used a variety of methods to identify amaranth seeds discovered in manure.

The researchers in the most recent study compared six different techniques for isolating palmer amaranth seeds from manure:

  • Dry sieving, where manure was oven baked and then forced through a No. 18 and No. 40 sieve.
  • Rinse sieving, where manure was mixed with 100 mL (about 1/3 cup) of water, then sieved with water
  • Manure Saturation Sieving, where the manure was mixed with 600 mL (about 2 cups) of water, then sieved
  • Manure Saturation Sieving with blending, which incorporated an immersion blender
  • Dispersion sieving, which added Calgon, baking soda, and epsom salt before seiving
  • Dispersion sieving with blending, which incorporated an immersion blender

Researchers also used two types of manure: one type without bedding and another type including bedding.

The slightly less complicated method worked best, researchers wrote.

"The highest percentage of seed recovery was found with the rinse sieving method (>90% recovered) in both manure types, with or without bedding, while the lowest was with the dispersion method with or without blending (<24.7% recovered)," they wrote. "This was surprising as the dispersion method is often used for separating weed seed from soil."

The results could have implications for presenting the weed's spread, but also help prevent other manure-based weed transmission, researchers wrote.

"Rapid detection is beneficial in a multitude of ways that will help prevent or reduce the spread of Palmer amaranth, or other weed species of concern, into regions where it has not been previously established," they wrote.

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