Harvest management (Three-cut, Stubble height: grass , Stubble height: alfalfa-grass )
Three-cut intensive grass management
We suggest three cuts/season for much of the Northeast. The first two cuts are taken for lactating dairy feed, with a goal of 50% NDF. A third harvest in the fall for dry cow forage can be taken when convenient. The general harvest management scheme is to harvest in mid-late May at a late boot stage before heading. The second harvest should occur 30-35 days later, as the quality decline in regrowth is as rapid as in spring growth. Take a third harvest in September. The first two harvests should be of optimum fiber content with an acceptable CP content (approx. 15-18% CP). No matter when the fall harvest is made, this forage will be low in CP, low in NDF and relatively low in digestible fiber. Fall-cut grass also tends to be lower in potassium than spring cut forage, making it a reasonable dry cow feed.
Stubble height issues: grasses
Recent studies with corn harvested for silage suggest that increasing the stubble height will improve the nutritive value of corn silage (Lewis et al. 2004), but this directly impacts the grain to stover ratio in grain crops. It is obvious that fully headed perennial grass cannot be turned into high quality forage through increased stubble height. It is not clear, however, if grass slightly past the optimum harvest window can be salvaged for lactating dairy feed by using a higher stubble height.
We studied the feasibility of harvesting grass at a higher stubble height to improve forage quality (Cherney and Cherney, 2005a). 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 in 2001, 2002 and 2003 just past optimum fiber content, with NDF in the mid to upper 50’s. Two sites were sampled, a fertile site in Ithaca, NY and a more marginal high elevation site in Dryden, NY. Rates 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. 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. 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. 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. 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.
Stubble height issues: alfalfa-grass
Stubble height has more of an impact on alfalfa quality than it does on grass (Table 2). A Wisconsin study looked at the impact of stubble height on alfalfa yield and quality (Wiersma, 2000). Both small plot and field scale experiments were conducted. On average for spring harvest, alfalfa yield changed 470 lbs/inch, while grass averaged 207 lbs/inch. NDF in alfalfa changes approximately 1 unit per inch, while it changes only 0.38 units/inch for grasses. Once a grass nears heading, the top of the plant is relatively high in NDF. The top of an alfalfa plant is more immature at harvest compared to grasses, considerably lower in NDF than the lower stem. Increased stubble height when cutting alfalfa-grass stands, however, is not economical. For alfalfa-grass stands it is best to cut as low as possible. The exceptions to this rule relate to stand persistence of alfalfa. Winter-damaged alfalfa should be cut higher in the spring, and a higher stubble height might be helpful on alfalfa-grass stands in the late fall to help catch snow.