LOVELOCK - It seems I often receive calls from local producers shortly after the morning coffee shop crew adjourns for the day. Recently, I received a call asking, "What is the best height to mow forages for hay?"
Well, I gave them my usual extension educator reply, "That depends..."
When cutting forages for hay there are a few things we need to clarify:
Are you harvesting grass hay or alfalfa hay? What are your hay quality and yield goals? What condition are your forages in? (Are they stressed from soil conditions, lack of water or other factors?) How level are your fields?
In doing an Internet search for research on cutting height of forages, I found numerous studies and articles that included recommendations for both alfalfa and grass hay. However, most of the studies found were conducted prior to 2000.
An article written in 2007 by Daniel Wiersma, Mike Bertam, Ron Wiederholt and Nick Schneider, "The Long and Short of Alfalfa Cutting Height," documented the following studies.
Early Wisconsin studies on alfalfa harvested three or four times per season yielded more tons of forage when cut at a one-inch height versus cutting at three inches or more (Kust and Smith, 1961, Smith and Nelson, 1967).
Research conducted in North Dakota since the mid-1960s demonstrated similar results, where shorter cutting heights lead to higher yields. In a recent North Dakota two-year study using three or four-cut systems, annual alfalfa yields were reported to be 1.6 tons per acre higher when cut at one inch compared to five-inch heights (Meyer, 1999).
Research at the Wisconsin's Marshfield Agricultural Research Station (MARS) showed a reduction of a one-half ton of dry matter per inch as cutting height increased from two to six inches (Wiersma, 2000).
These studies indicate that there is a forage yield benefit to cutting at shorter heights. Most of that gain isn't simply from harvesting more of the plants at each cutting. It's from increased growth from stems originating from the crown rather than from axillary buds on the lower portions of the stems.
So if increased yield is a benefit to reducing cutting height, what are the disadvantages? First, you need to watch when you get down to lower cutting heights, because of the increased risk of scalping an uneven field or one with excessive gopher activity.
Cutting forages at lower heights can damage equipment and increase the amount of dirt and debris in the forage. Other issues include hay quality and stand longevity.
So the next question is, "How does lowering the cutting height affect the quality?" A study conducted in Nebraska (Ogden and Kehr, 1968) evaluated the top half of a full bloom alfalfa canopy with the bottom half. Results indicated that the top half of the canopy had a higher percentage of the digestible nutrients and less fiber then the bottom half of the plant.
The lower stem portions (bottom two thirds) decrease in quality at a faster pace than does the upper portion of the stem. This occurs because the lower stem sections are more mature and tend to be more fibrous and woody compared to the less mature upper stem sections.
A Wisconsin study confirmed quality diminishes modestly when alfalfa is harvested closer to the soil surface. Crude protein was increased by less than 1 percent when cutting height was increased from two inches to six inches.
However, milk produced per acre results from this study indicated that more milk per acre is generated at lower cutting heights. The quality improvement obtained by increasing the cutting height is not enough to offset the yield reduction. The amount of quality gain must be weighed against the yield loss due to leaving taller stubble. If growers are harvesting in a timely manner, there should be no reason to forego yield for a slight quality increase due to leaving taller stubble.
When changing forage management practices, growers want to be certain that stand longevity is not jeopardized. While alfalfa has a deep taproot and crown that store the reserves for the new alfalfa to grow from following a cutting, most grasses lack a deep root system and have to re-grow from the stubble that is left after cutting. If you cut grasses too short you are robbing the plant of the energy reserves it needs to re-grow.
Cutting alfalfa shorter can reduce stand life if other stress factors exist. Frequent cutting of alfalfa at very early maturity stages often depletes root carbohydrate reserves. When carbohydrate reserves are low, energy for stem regrowth is low and results in poor plant recovery after harvest.
In spite of this, cutting height research shows that early plant decline or death does not occur for alfalfa when proper crop management practices are used. When plants are healthy and not under stress, it appears that short cutting heights will not reduce stand longevity.
One exception to lower cutting heights for alfalfa is when harvesting alfalfa in the fall increased cutting heights may be warranted for the purpose of catching snow. Longer stubble catches snow and may help keep the snow cover for a longer period of time. Snow cover can protect alfalfa plants from cold temperature extremes or fluctuating late winter temperatures.
Higher incidence of root heaving was documented for one or two-inch cutting heights compared to a four-inch cutting height (Belesky and Fedders, 1997). From this study, it appears that leaving a four-inch or greater stubble in the late fall may be helpful to prevent root heaving in the spring.
As for grass forages, research conducted at Miner Institute, Chazy, NY, studied the effect of cutting height on orchardgrass and reeds canarygrass in a greenhouse experiment. This work showed that first year reeds canarygrass was completely killed at a two-inch cutting height, while the orchardgrass did regrow, but at a much slower rate. In contrast, at the four- inch cutting height both grasses performed fine with the reeds canary grass measuring 16 inches of regrowth in 21 days (Thomas, 2006).
Here are the take home points to remember:
Cut healthy, non-stressed alfalfa fields at one-inch heights to achieve maximum dry matter and nutrient yields.
In fields where plants are experiencing moisture or flooding stress, or where the crop has been cut early and frequently, root carbohydrate reserves may be low and cutting height should be adjusted upward to avoid additional stress or plant death.
Adjust cutting height to avoid injuring plants, contaminating the forage with soil, or picking up rocks. If harvesting forages in the fall, growers should leave a four-inch or greater stubble to help capture snow and prevent heaving.
Grasses - minimum of three to four inches of stubble should be left to maintain stand longevity.
Stands could be even more sensitive to cutting height reduction in the seeding year. The loss in grass stand productivity from cutting too low far outweighs any yield boost you might get from harvesting a few extra inches in that one cutting
In mixed stands cutting height could actually be used as a management tool for stand composition by choosing a cutting height that either favors grass or alfalfa.
Sources: "Grass Cutting Height," Joe Lawrence, 2010, Cornell Cooperative Extension Lewis County.
"The Long and Short of Alfalfa Cutting Height," Daniel Wiersma, Mike Bertam, Ron Wiederholt and Nick Schneider, 2007, Marshfield Agriculture Research Station.[[In-content Ad]]
