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Grass stubble height research study

We studied the feasibility of harvesting grass at a higher stubble height to improve forage quality [GIS-23]. Orchardgrass, reed canarygrass, and tall fescue were fertilized with 0, 100 and 200 lb N fertilizer/acre at spring greenup and sampled in late May or early June for 3 years, just past optimum fiber content, with NDF in the mid to upper 50’s. Rate of change per inch of increased stubble height on a percentage basis was small for forage quality parameters, resulting in small changes in milk/ton (0.83 + 0.42%) and relative forage quality (1.7 + 0.84%) estimates per inch. The much greater change in yield compared to quality with increased stubble height resulted in a -5.4 + 1.3% change in milk/acre/inch.

Once first-cutting perennial grasses have past the harvest window for optimum forage quality, raising the cutter bar at harvest will not improve overall quality sufficiently to warrant this practice as a management tool. We sampled just past optimum quality, so cutting at a more mature stage would have even less impact on forage quality. The small increase in forage quality with increased stubble height does not offset the significant loss of DM yield, regardless of grass species or level of N fertilization.

Conclusions:

  • Increased cutting high enough to increase forage CP by one percentage unit, or to reduce NDF by one percentage unit, reduces overall DM yield by 12% on average.
  • Application rate and timing of application of manure had a very minor affect on forage nutritive value.
  • By the second year of the study the highest rate of manure application yielded more DM than recommended N fertilizer applications.
  • There is no reason to cut perennial cool-season grasses any higher than the minimum stubble height needed to avoid hitting stones or soil in rough fields.