DISC MOWERS DAMAGE GRASS IN GRASS-ALFALFA MIXES

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            by Bruce Anderson, 

Extension Forage Specialist

University of Nebraska-Lincoln

               Disc mowers are fantastic machines.  Compared to sickle bar mowers, they cut faster, have less maintenance and repairs, and rarely plug.  They can cut the crop shorter and keep going even if they occasionally scalp the surface.  And that’s the problem!

               `With alfalfa, regrowth comes from crown buds using nutrients stored underground in the taproot.  It doesn’t matter if you leave a 1-inch or a 4-inch stubble, alfalfa regrowth rate will be the same.

              

Grasses are different.  Grasses depend on nutrients stored in the lower stem for early regrowth.  And some grasses, like orchardgrass, fescue, and festulolium that have very low basal leaves, they also use energy produced by photosynthesis in those basal leaves for regrowth energy.  So, cutting these grasses short results in much slower regrowth and a weakening of the plant because the source of energy to support regrowth has been removed.

               In a grass-alfalfa mixture, the short stubble left by a disc mower delays and slows the regrowth of the grass while the alfalfa recovers at its usual rate. Pretty soon alfalfa gets several inches taller than the grass, forms a tight canopy, and shades out the grass growing underneath.  Before long the grass dies out and disappears.

               Clearly, the solution is to raise the cutting height to around 3 to 4 inches like happens naturally with a sickle bar.  This is easier said than done, however.  First, you need to remember to leave a taller stubble.  And if working with a custom operator, it probably will require reminding that person of your stubble height demands.

               Keeping grass in alfalfa when cutting with a disc mower is challenging, but it can be done.