Timing the first alfalfa cutting
How do you decide when to make your first cutting of alfalfa each year? Do you use a calendar date? Perhaps you use another method to determine when to make the first cutting. There are a number of considerations. It’s an important decision.
Obviously, you do not harvest the first crop by the same calendar date year after year. Growth and development of alfalfa responds to temperature and moisture, and every spring is different.
Using the PEAQ (Predictive Equation for Alfalfa Quality) method is an easy and quick technique that provides an in-field forage quality estimate relative to plant height and stage of maturity. Its purpose is to just get you in the ballpark of your desired harvest quality goal. PEAQ instructions are available at .
Some growers use growing degree days (GDD) to time their first cutting. The GDD method is similar to PEAQ in that it is based on research of many alfalfa varieties over many years correlating forage quality to plant growth and development. More specifically, GDD estimates neutral detergent fiber (NDF) levels relative to accumulated GDDs with calculations starting on March 1 with a 41-degree-F base temperature.
The daily calculation is [(maximum temperature + minimum temperature)/2] – 41. For example, say the maximum temperature is 70 degrees and the minimum is 50 degrees during a 24-hour period. Adding those, you get 120. Divide by 2 and you get 60. Subtract 41 and it figures out to 19 growing degree days for that day. The GDDs accumulate daily as you begin calculating on March 1.
Based on research at Michigan State University, alfalfa averages 30%, 40% and 45% NDF at about 600, 750 and 970 GDD, respectively. However, this method doesn’t appear to be any more accurate than PEAQ, and extreme weather conditions could adversely affect the relationship of GDD calculations versus actual growth and development.
What’s the most accurate?
The scissor cuts method is the most accurate. With a scissors, you cut some samples of alfalfa plants growing in the field. Collect these samples of the standing crop forage twice a week and send them to a testing lab. Have the samples tested using near-infrared spectroscopy (NIRS). This is certainly more costly and labor-intensive then the other methods, but the results are a much more accurate representation of standing crop forage quality.
Whether using PEAQ, GDD or scissor cuts, keep in mind these are in-field stand crop measurements, and you still have to estimate forage quality loss from harvest and storage to reflect the end product. In PEAQ, the loss of dry matter from harvest and storage of haylage and hay equate to a reduction in relative feed value (RFV) of about 15 to 20 units. Therefore, to end up with 150 RFV alfalfa, it is recommended to harvest when PEAQ measurements predict 165 to 175 RFV for the standing crop.
In general, for harvest of first-cutting of alfalfa in the spring, the cutting is made in bud stage for dairy and bloom stage for beef. Harvesting alfalfa at bud stage provides higher quality and is on schedule for a four-cut or even a five-cut season, although regrowth sometime in the year should be allowed to reach bloom stage at least once to replenish crown/root carbohydrate storage for better plant health.
You can't control the weather. But there are a number of things you can do to help maximize the production and quality of your alfalfa crop.
• Cutting height. Cutting height can have an impact on both yield and quality of alfalfa harvests. Target a cutting height of 2 to 3 inches above the soil for alfalfa, but no shorter than 4 inches for grasses. Alfalfa regrows its most robust, higher-yielding shoots from the crown of the plant, and stores its regrowth food reserves in the crown and upper taproot.
While cutting alfalfa plants this short also reduces forage quality a little, the better yield potential from cutting low maximizes milk per acre. However, most grasses store regrowth reserves in the lower stem, and cutting grasses too short can reduce their regrowth potential.
• Mower type. Sickle cutter bars have the benefit of slightly lower respiration losses of alfalfa plants versus using a disc cutter. And a sickle bar’s cost is 10% to 20% less per foot, and they require about 50% less power per foot. However, disc-type cutters or discbines handle higher volumes at twice the field operation speed of a sickle, and their higher operating cost is more than offset by labor savings. One caution when using a discbine is to properly adjust the cutter bar angle so as to avoid contact with soil to minimize ash content in the harvested forage.
• Conditioner. Flail/impeller type conditioners were developed for grass production, not alfalfa. They tend to have a 2% to 3% higher dry matter loss versus rollers for conditioning alfalfa.
• Swath width. One of the most important aspects of alfalfa harvest is to create a wide swath. University of Wisconsin research clearly shows a wide swath maximizes drying time. This reaches the desired harvest moisture faster (hay or haylage), which reduces dry matter loss in the field and improves forage quality. A 12-foot cutting width laid in a 9-foot-wide swath instead of a 6-foot swath has shown a 35% faster drying time. The wider swath can reach 65% moisture content in five to eight hours, allowing haylage harvest in a day, and reaching dry hay conditions at least a half-day faster.
• Wheel traffic. Wheel traffic should be minimized as much as possible. Use equipment only large enough to do the task. What about merging two windrows together? Mergers can be advantageous in reducing overall traffic where the harvest equipment can handle the larger-volume windrows. If you need to drive on fields for manure application or other purposes, do it as soon as possible after harvesting alfalfa. When a field is driven on, the yield loss for the next crop in the wheel tracks two days or five days after harvest is about 13% and 28%, respectively.
• Storage. Proper storage of hay is critical. Typical dry matter loss of hay stored outside on the ground and not covered is 15% to 30%. In other words, your $150-per-ton alfalfa just lost $22 to $45 per ton in value. With numbers like those, it doesn’t take long to afford shelter for hay storage.
Lang is the Iowa State University Exten-sion agronomist at Decorah in northeast Iowa. Contact him at .
This article published in the May, 2015 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2015.