Alfalfa scissors cut sampling procedure
To estimate the pre-harvest quality of alfalfa, producers can use the scissors cut method. This involves regularly collecting alfalfa clippings from the field, and analyzing the samples.
How it works
Which fields to sample
Select fields in the second production year for alfalfa or the first production year for red clover and grasses. To ensure you get the most accurate results possible, take field samples that are representative. This is particularly true if the field has a mix of species, because forage quality varies among forage crops.
When to collect samples
Begin collecting samples in mid-May, or when the alfalfa is about 14 inches tall.
Take samples twice a week until forage quality falls below desired harvest quality. We recommend taking samples on Monday and Thursday, so results can be available on Tuesday and Friday.
Sample in the early morning, before 8 am. This reduces day-to-day variability due to differential accumulation of nonstructural carbohydrates in the leaf on sunny vs. cloudy days.
How to clip the alfalfa
Cut samples 2 to 3 inches above ground level (similar to harvest height) and repeatedly take them within the same small area (0.5 acres or less) of field. Be sure selected plants are random -- don’t just take the largest plants.
Collect fresh weight sample of approximately an 0.5 pounds (225 grams) by sampling approximately six plants. The laboratory will subsample large samples, which may increase error. It’s best to collect and report on two subsamples per field.
Place the sample in a paper bag and take it to a forage quality testing laboratory. Sample drying during handling prior to analysis isn’t a concern because results will be expressed on a dry matter basis.
Select a laboratory certified by the National Forage Testing Association to run the samples. Let the laboratory know the sample is fresh. Request wet chemistry unless the laboratory assures you they have a separate near infrared spectroscopy (NIR) equation for fresh samples.
Note that frequently immature alfalfa samples have high levels of pectin. Pectin remains in the acid detergent fiber (ADF) fraction. For immature samples, this sometimes causes ADF to be much closer to neutral detergent fiber (NDF) than the 8- to 10-point spread we usually see on samples harvested for hay or haylage.
We recommend cutting alfalfa for dairy cows at a relative feed value (RFV) of 170 to get an RFV of 150 (assuming 15 percent field quality losses during harvesting) at feeding. Harvest red clover at an RFV of approximately 180 to get the same animal performance as alfalfa with an RFV of 170.
Ration goals may vary, depending on other ration ingredients, herd production goals and other factors. Discuss your ration goals with a nutrition advisor.
Interpreting scissors cut results
We recommend the following four steps when using scissors cut data to plan harvest schedules:
1. Set harvesting goals.
Match forage quality to animal needs. We recommend that alfalfa/grass forage quality be 150 RFV for milking dairy herds and 120 to 130 RFV for heifers, stocker cattle and lactating beef cattle. Red clover should be about 10 points higher in RFV.
Ration goals may vary, depending on other ration ingredients, herd production goals and other factors. Discuss ration goals with a nutrition advisor.
2. Adjust for field losses.
Under the best conditions, you’ll lose 15 percent (points) of the dry matter during harvesting.
This is why you should cut a field at 165 to 170 RFV, so end up with harvested forage of 150 RFV. Individual farm experience is an important consideration.
3. Adjust for total harvesting time.
Begin harvest even earlier to average 150 RFV for all fields. Research from the University of Wisconsin has shown that alfalfa’s RFV will decrease at a rate of 4 to 5 units per day during the late vegetative and flowering stages. Take this forage quality change into consideration when planning the first cutting.
For example, if it takes two weeks to harvest first cutting and we want to average 150 RFV, begin harvesting one week before RFV 170, as described previously. Seven days multiplied by a 4 or 5 RFV change per day equals 28 to 35 points RFV. This farm should begin harvesting when the scissors cut results indicate standing forage quality is 198 to 205 (170 plus 28 and 170 plus 35).
4. Adjust for local field conditions.
Scissors cut results generally are for alfalfa forage quality, though some councils are doing other forages such as small grains or clover. This means grassy fields will reach the stated forage quality earlier than pure alfalfa.
Stands on lighter soils will tend to begin growing earlier and mature faster, unless conditions are droughty. South slopes will also mature earlier than north slopes. If you’ve planted some of the newer, high-quality varieties, these should reach the desired forage quality two to three days later than standard varieties.
Reviewed in 2018