By Stephen K. Barnhart, Department of Agronomy
Producers must answer a couple of basic questions when deciding the time of the first spring cutting of alfalfa and mixed alfalfa and grass fields. What's your hay harvesting schedule? What are your objectives for the harvested hay crop or forage stand? Harvest schedule decisions tend to be guided by what's most important. Producer objectives may include harvested yield, nutritive quality of the forage, or vigor and persistence of the perennial stand.
Reaching a high level of all three objectives is unlikely with a single chosen harvest schedule. Producers can generally meet two of the three with a chosen harvest schedule, but not all three. So, there are usually some compromises when harvesting.
In general, more frequent harvests produce forage of higher nutritive quality at an acceptable yield level, but at a sacrifice in stand vigor or longevity. Conversely, less frequent harvest will produce acceptable yields and a greater degree of stand persistence and plant vigor, but forage of a lower nutritive value.
Maximum dry-matter yield of alfalfa and most forages is often obtained by harvesting the first cutting of the season at nearly full bloom and harvesting subsequent cuttings at 40 to 45 day intervals until late August or early September, referred to as a "3 summer-cut system." This system produces forage relatively lower in nutritive quality.
Such forage is suitable for livestock on maintenance rations, or slower weight gain livestock enterprises and can be used in low-performance feeding programs. To add additional harvested yield, growers who use a 3 summer-cut system will often harvest a fourth cutting in mid to late October.
For higher value forage
In contrast, high-performance livestock feeding programs require higher nutritive value forage. The optimal compromise for higher forage quality and dry matter yield of alfalfa is to harvest the first cutting at the late-bud to first-flower stage and to make subsequent cuttings at 32-to-35 day intervals until late August or early-September, often referred to as a "4 summer-cut system."
Growers using a 4 summer-cut system will sometimes harvest a fifth cutting in late fall, also typically high nutritive quality forage. This latter 4 summer-cut system has led to a greater stand reduction and shortened stand longevity than those managed under a 3 summer-cut system. The negative impact on stand vigor and longevity are usually made worse when a late autumn cut is added to either the 4 summer-cut system as a fifth cutting, or to a 3 summer-cut system as a fourth cut.
Alfalfa and alfalfa-dominant mixed legume/grass stands mature more quickly and lose nutritive quality faster during the first growth cycle of the spring, than during summer growth cycles. Growers desiring high-quality alfalfa hay at first cutting must manage the first seasonal cutting more closely to meet their forage quality goals.
To complicate this management even more, each spring growing season is a little different and may be a week or more different from one year to the next in the rate of crop development. Growers managing for high quality are encouraged to use one of the "heads up" methods for predicting the quality of the standing crop in the field.
Predicting crop quality
There are several ways to decide when to cut, if you know what relative feed value (RFV) you need. You could go by the calendar and plan to cut at the same time you cut last year — but with the year-to-year variations in seasons, that's really not a good system.
Another way is to look at the stage of development of the alfalfa. To do that, you need to understand how alfalfa grows. The first developmental stage is the vegetative stage when no buds have appeared. Forage quality at this stage is often too high for most livestock. Next is the early- through late-bud stage. In early-bud, you can't see the bud yet, but you can feel it in the stem tips. In late-bud, there's a large, visible bud, just before open bloom. Then comes bloom stage, followed by the seed pod stage when the nutritional value of the plant is decreasing rapidly with each day of harvest delay.
For high-performance animals, the first cutting should be made from early to mid-bud. For beef cows, late-bud through mid-bloom is fine, and for dry, open ewes, the full bloom stage is acceptable.
In Iowa, alfalfa bud stages generally occur around mid-May when producers would typically make a first cutting for dairy cattle. But keep in mind that spring this year may be a few days ahead of normal, so relying on last year's first cutting date may not be appropriate this year.
Once a first cutting is made, bud stages on the regrowth generally occurs again about every 30 days after cutting, allowing four bud-stage, dairy quality cuttings per season. Your most critical decision then, is when to make that first cutting.
Predicting forage quality in the standing crop
There are a couple 'predictive methods' that may be helpful. These are referred to as the Predictive Equations for Alfalfa Quality (PEAQ) or the 'scissors clipping' method. Both methods provide an in-field estimate of preharvest quality of standing alfalfa. They are indicators of quality, but they're not intended to be used as the basis for ration balancing and do not account for harvest or storage losses.
The scissors clip method involves taking hand clippings at harvest height in several places within a field, twice per week leading up to first harvest. Samples should be no more than one pound fresh weight, and delivered to a forage testing lab for analysis using Near Infrared Reflectance Spectroscopy or NIRS for fresh tissue.
The PEAQ method predicts RFV and fiber content by identifying the maturity of the most mature stem in a 2-square foot area, and the height of the tallest stem in the area. These two characteristics are applied to a chart, or to a more user-friendly PEAQ stick, to estimate the Relative Feed Value (RFV) or Relative Forage Quality (RFQ) of the standing crop. A full explanation of the PEAQ method and procedure is available online. Below is the chart to use with the PEAQ predictive method.
Using either scissors clipping or PEAQ, another calculation must be made for anticipated harvest and storage losses that will occur. Generally, 10 percent to 15 percent harvest and storage losses are anticipated. So for each bi-weekly sample, about 10 to 20 RFV or RFQ units should be deducted from that of the standing crop.
Forage grasses develop similarly
As forage grasses mature, yield at cutting increases and plant vigor and persistence improves, but feeding value declines. For most of our forage grasses, the first growth of the spring also has a seed stem that both adds yield and reduces feeding value faster with advancing maturity.
The cutting decision for 'all grass' and grass-dominant mixed hay should be based on the feed quality needs. Grass is considered higher in fiber than alfalfa, so, alfalfa and alfalfa-dominant hay mixtures of less than 20 percent of the stand or hay composition is generally recommended for lactating dairy cattle. For other classes of livestock, harvesting at seed head emergence or soon after is the most common harvest 'target'. Waiting to harvest forage grasses that have matured into the seed formation stages generally does not add significantly to the yield, and produces lower and lower feeding value hay.
Stephen K. Barnhart is a professor of Agronomy and the Iowa State University Extension forage agronomist. He can be reached at 515-294-7835 or by emailing firstname.lastname@example.org.