By Justin Brackenrich and Leanna Duppstadt et.al
Fall is an important time to ensure that hay fields are properly managed, and attention to detail will help to ensure their survival through the winter. Fall harvest management can be the greatest determining factor of forage stand longevity. Mismanagement during harvest can result in reduced plant carbohydrate storage for winter and less root mass for nutrient and water uptake.
Alfalfa stores carbohydrates below ground in a taproot and just above ground level in the crown. Grasses, however, store most of their energy in the first three inches of stem or in tillers. In fall, more than ever, maintaining these stored carbohydrates means that the plant will be able to regrow and tolerate the upcoming cold weather. During the season, cutting heights are often 2" for legumes and a minimum of 3" for grass stands. However, fall cuttings of alfalfa and grass should both have no less than a 4-inches of stubble height by the first frost. This ensures enough plant material is present to photosynthesize and rebuild carbohydrate stores necessary to over-winter. When working with mixed stands, be sure to manage the field based on the predominant species. For more on cutting heights, read Penn State's Cutting Height in Forages: How Low Can You Go?.
Root Mass and Regeneration
In cool-season grasses, below ground development is directly reflected in what's above ground. This means that as we harvest below the minimum height of 3" and remove too much leaf tissue, we can slow root growth, and even have the potential for roots to be cast off. Why is this a concern? Roots are where the plant captures water and nutrients needed for above ground growth. Information provided by Michigan State University shows that removing 50% or less of leaf volume will result in little to no damage to root structure. Once leaf volume removal is 70% or higher, almost 80% of root growth will stop. This stoppage in root growth can result in slowed or even halted regrowth.
Another factor to consider is if your crop has foliar, crown, or root diseases. For many of the pathogens that cause these problems there is a risk of disease in the subsequent growing year as the pathogen(s) can often overwinter in plant biomass if environmental conditions are favorable. Proper harvest schedule and limiting thatch, or infected crop residues, can reduce spread of foliar diseases. Some examples of these include crown rust, stem rust, and leaf rust of cereals, as well as brown stripe of orchardgrass. More information on grass diseases see the Penn State Extension article "Identifying late season diseases in forage grasses".
Grass management and winter damage concerns are different than alfalfa for a couple of reasons.
First, grass stands are usually made as dry hay, so it needs hot, dry air temperatures to achieve the less than 20% moisture to be safe. Cutting grass hay into October makes it almost impossible to get dried, therefore, most dry hay production will stop in September, leaving the preferred four to six weeks of regrowth, by default. As wrapping and baleage has become more popular, the risk of damage increases as we push later into the year, but risk is still low when leaving adequate stubble.
Second, Pennsylvania farmers predominantly use cool-season grasses which continue to grow longer into the year until 25 degrees F is reached for a prolonged period.
Third, is the lack of crown damage that is seen with alfalfa (less issue with heaving and splitting) compared to grasses. Since our grasses have hair roots vs. alfalfa's taproots and are either sod-type grass or bunch-type grass, damage to a small portion does not kill the entire plant but rather damages that area or the leaf issue.
The keys to successfully overwintering grass fields are four to five inches of stubble, and adequate phosphorous and potassium for hardiness and tillering.
Historically, it is recommended that the final cutting of alfalfa be removed no later than 4-6 weeks before the first killing frost – and this advice is still viable today! This will help ensure plants have adequate time to regrow and store the necessary nutrients while restoring roots to over-winter and begin growth in the spring. Before deciding whether to make a final harvest later than the traditional, "safe" harvest window of 4-6 weeks before a killing frost, several aspects should be assessed.
With more winter-hardy varieties of alfalfa available, tradition is beginning to be tested with producers taking their final cutting later into the fall. If winter-hardiness is part of the improved genetics utilized on your operation, the improved winter-hardiness could possibly allow the alfalfa to withstand a slightly later cutting. With that said, it is always important to understand your variety and know that improved winter-hardiness does not mean push the envelope as far as possible.
Alfalfa stand age is also indicative of whether a later cutting should be removed. Typically, older stands of alfalfa are more prone to winter kill and should not be mowed past the recommended 4-6 week "critical period" before a killing frost. If the alfalfa stand has not been allowed to flower at least once during the growing season, no matter the variety, it is at a much higher risk for winter kill and therefore should not be harvested after the 4–6-week period before a killing frost.
It is important to remember that taking a later cutting (after the critical period but before a killing frost), spring yields may suffer, especially with the first cutting. So, when deciding whether it is worth it for your operation, the benefits need to be weighed with the risks. Often in fall cuttings, the yields are low, but the machinery costs are the same as any other cutting. This makes the price per ton very different. Make sure to factor this into your decisions when thinking about cutting or not.
Some information for this article came from Michigan State University's article Cutting Management for Cool Season Forage Grasses and Ohio State University Time to Take the Last Forage Cutting.Source : psu.edu