Dirty TMR’s Low cutting heights can raise ration ash content

May 15, 2009 07:00 PM

The need for speed in cutting hay crops has meant a boom in the use of disk-type mower/conditioners.

But low cutting heights—2" or less—have also meant that more soil and dirt is tossed into windrows and ultimately ends up in feed bunks.

"Disk mower/conditioners are dual-purpose machines—they mow grass and level land,” quips Ev Thomas, an agronomist with the Miner Institute in Chazy, N.Y.

Normal ash content in rations is 6% to 7%. "Some producers are reporting up to 16% ash in rations,” Thomas says. "If you're seeing ash levels above 10%, you may want to look at your mowing heights.”

Research at Miner Institute indicates slightly higher forage quality when alfalfa/grass mixtures are cut at 4" rather than 2". However, dry matter yields were 0.5 tons/acre less at the higher height over three cuttings. That resulted in 1,200 lb. less milk production per acre.

If ash content is not a problem, Thomas still recommends a 2" to 2.5" cutting height for alfalfa/grass mixes, with some exceptions:
  • In one trial, reed canarygrass died when harvested at 2". When harvested at 4", it regrew to 16" in 21 days.
  • Orchardgrass cut at 2" took 38 days to grow to 16".
  • If mowing grass, cut at 3" because grass stores carbohydrates in the bottom 3" to 4" above the ground. Cutting lower than that reduces the plant's ability to recover.

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