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Mechanics Corner: The lowdown on mowing hay

Josh Vrieze for Progressive Dairyman Published on 05 May 2017
Pitch of cutting disc is important

When mowing hay, numerous management decisions contribute to total yield, forage quality and stand longevity.

This includes whether you’re harvesting grass hay or alfalfa hay, your preferred cutting height and when the first cutting takes place. In addition, mower selection and maintenance can also impact your operation in terms of productivity and profitability. This article explores some of the crucial decisions that should be considered before hooking up your mower, hitting the field and making your first cut of the hay season.



Maturity stage matters

Maturity stage at harvest is the single-most important factor influencing the quality of your forage, according to the University of Massachusetts – Amherst (UMASS) Extension. This is because as forage crops mature, fiber content increases and quality diminishes. Therefore, striving for maximum yield can come at the expense of quality.

The UMASS Extension report states, “When producing forages, especially legumes, if the goal is (achieving) the highest quality, this will tend to shorten stand persistence and decrease yield. Maximum yield of alfalfa is achieved at the stage of full flowering, whereas quality is highest prior to flowering.”

Three cuts or four?

According to Iowa State University Extension, harvesting more frequently produces forage of higher nutritive quality at an acceptable yield level but negatively impacts stand vigor and longevity. Conversely, harvesting less frequently will produce acceptable yields and a greater degree of stand persistence and plant vigor – but forage of a lower nutritive value.

In order to maximize dry matter yield, Iowa State Extension recommends a “three summer-cut system,” which means a first cutting at nearly full bloom and harvesting subsequent cuttings at 40- to 45-day intervals until late August or early September. (This time period can vary based on climate).

A “four summer-cut system” can help strike a balance between maximizing forage quality and dry matter yield. For this, Iowa State Extension recommends harvesting the first cutting at the late-bud to first-flower stage and harvesting subsequent cuttings at 32- to 35-day intervals until late August or early September.


Cutting height

Studies performed by University of Wisconsin Extension showed that forage yield increased as cutting height was reduced. For instance, on average, total alfalfa yield increased by 0.5 ton dry matter per acre for each 1-inch reduction in cutting height. Forage quality, however, decreased as cutting height was reduced.

In order to maximize forage quality and dry matter yield on subsequent cuttings, a cutting height of 3 inches for alfalfa and 4 inches for grasses is recommended. The reason for this is the main growing point for grasses is above the ground, so cutting below 3 inches means it will take longer for the crop to regenerate, which limits the yield of the next cutting.

With alfalfa, everything below 3 inches is mostly stem. The leaves which contain all the nutrients stand at 3 inches and above, so cutting lower means you get a little higher yield but no additional nutrients for your cattle.

A lower cutting height could lead to greater amounts of ash and rocks in the crop, giving producers yet another reason to select a higher cutting height. To minimize dirt and ash contamination and achieve a clean cut of the crop, it’s best to keep a close eye on the pitch of the cutter bar.

Some operators tend to set the pitch of the cutter bar downward at too steep an angle. On Vermeer trailed mowers, it is recommended to angle the cutter bar upward to get a cleaner cut.

Choosing the right mower

The size and type of mower you want are the top things to consider when purchasing a new mower. In recent years, there has been a trend of producers moving from traditional three-point mowers to trailed mowers, which allow them to go from multiple three-point mowers, tractors and operators down to one of each.


The main knock against three-point mowers is that they can tie up extra tractors, extra operators and consume extra fuel. Larger trailed mowers help producers increase mowing capacity while reducing fuel consumption, maintenance and labor costs.

Don’t forget mower maintenance

For those of you who already own a mower, you can turn your attention to pre-season maintenance. Be sure to check your owners manual for daily and regular service and maintenance needs to optimize the performance of your mower. Here are some general tips for inspecting your mower:

  • Lube: Oil and lubrication points should be inspected regularly. The gearbox oil, driveline and PTO shaft are particularly important. Make sure the PTO slides in and out smoothly; otherwise you risk breaking off the shaft.

  • Cutter bar: Check the cutter bar to make sure it’s functioning properly. You should be able to spin the cutter bar around with one hand. If you can’t spin it, look under each of the discs to make sure there is no buildup of twine or other material.

  • Tires: Check the tires to make sure they are properly inflated.

  • Blades, discs and hardware: Make sure all blades, discs and hardware are attached and in good shape. Replace any broken or excessively worn parts. end mark

References omitted but are available upon request. Click here to email an editor.

PHOTO: The pitch of the cutting discs is important to adjust differently for grasses and legumes to achieve higher-quality feed. Photo provided by Vermeer.

Josh Vrieze is a corporation product manager with Vermeer. Email Josh Vrieze.