How To Sample


Begin collecting samples mid May. Select fields that are second production year for alfalfa or first production year for red clover and grasses. Samples should be pure species because results will largely be determined by percentage of mixture, if mixed species, which is unknown and not related to any other site.

Take samples twice weekly until the forage quality falls below desired harvest quality. We recommend taking samples on Monday and Thursday so that 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.

Samples should be cut 2 to 3 inches above ground level and taken repeatedly within the same small area (0.5 acre or less) of field. Be sure selected plants are random – do not take the largest plants.

Collect approximately 0.5 lb (225 g) fresh weight sample by samples approximately 6 half plants. Large samples will be subsampled in the laboratory which may increase error. It is best to collect and report on two subsamples per field. Place sample in paper bag and take to forage quality testing laboratory. Sample drying during handling prior to analysis is not of concern because results will be expressed on dry matter basis.

Select a National Forage Testing Association certified laboratory to run the samples. Notify the laboratory that the sample is fresh. Request wet chemistry unless the laboratory assures you that they have a separate NIR equation for fresh samples.

Note: frequently immature alfalfa samples have high levels of pectin. Pectin remains in the ADF fraction. The effect of this is that on immature samples, ADF is sometimes much closer to NDF than the 8 to 10 point spread we usually see on samples harvested for hay or haylage.

Recommend cutting alfalfa for dairy cows at RFV 170 to get RFV 150 (assuming 15% field quality losses during harvesting). Red clover should be harvested at approximately 180 RFV to get same animal performance as from 170 RFV alfalfa.

Interpreting Results

We recommend the following four steps when using scissors clip 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 for heifers, stocker cattle, and lactating beef cattle (red clover should be about 10 points higher in RFV).
  2. Make adjustments for field losses. Under the best of conditions 15% (points) of the dry matter will be lost during harvesting. Therefore it is necessary to cut a field at 165 to 170 RFV to end up with harvested forage of 150 RFV.
  3. Make adjustment for total harvesting time. We have to begin even earlier to average 150 for all fields. For planning purposes we can use the average first cutting forage quality rate of change of 3 to 4 RFV per day. Thus, if it takes two weeks to harvest first cutting and we want to average 150 RFV, we must begin harvesting one week before RFV 170 (from #2). Seven days times 3 or 4 RFV change per day equals 21 to 28 points RFV. Harvesting for this farm should begin when the scissors clip results indicate standing forage quality is 191 to 198 (170 plus 21 or 28).
  4. Make adjustments for local field conditions. The scissors clip results are generally for alfalfa forage quality (though some councils are doing other forages such as small grains or clover). This means that 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. Further, if you have planted some of the newer, high quality varieties, these should reach the desired forage quality two to three days later than standard varieties.
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