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Extension > Agriculture > Crops > Forage Production > Forage utilization and management > Using PEAQ for RFV and NDF field estimates

Using PEAQ for RFV and NDF Field Estimates

Estimating alfalfa RFV in the field using PEAQ

How to use this chart:

  1. Choose a representative 2-square-foot area in the field.
  2. Determine the most mature stem in the 2-square-foot sampling area using the criteria shown in the table at the right.
  3. Measure the length of the tallest stem in the 2-square-foot area. Measure it from the soil surface (next to plant crown) to the tip of the stem (NOT to the tip of the highest leaf blade). Straighten the stem for an accurate measure of its length. The tallest stem may not be the most mature stem.
  4. Based on the most mature stem and length of the tallest stem, use the chart at the right to determine the estimated RFV content of the standing alfalfa forage.
  5. Repeat steps in 1 to 4 in four or five representative areas across the field. Sample more times for fields larger than 30 acres.

Note: This procedure estimates alfalfa RFV of the standing crop. It does not account for changes in quality due to wilting, harvesting, and storage. These factors may further lower RFV by 15 to 25 points, assuming good wilting and harvesting conditions. This procedure is most accurate for good stands of pure alfalfa with healthy growth.

The general recommendation is to harvest when PEAQ Estimate or the Scissors Cut sample lab test is 15 to 25 RFV points higher than what you want to have in the feed manger. Talk to your nutrition advisor or local Extension Office for more information.

Height of tallest stem (From soil surface to stem tip)
Stage of the most mature stem
  Late Vegetative Bud Stage Flower Stage
  Vegetative (>16") No buds visible 1 or more nodes with visible buds. No flowers visible. 1 or more nodes with open flower(s)
Inches
Relative feed value
16 237 225 210
17 230 218 204
18 224 212 198
19 217 207 193
20 211 201 188
21 205 196 183
22 200 190 178
23 195 185 174
24 190 181 170
25 185 176 166
26 180 172 162
27 175 168 158
28 171 164 154
29 167 160 151
30 163 156 147
31 159 152 144
32 155 149 140
33 152 145 137
34 148 142 134
35 145 139 131
36 142 136 128
37 138 133 126
38 135 130 123
39 132 127 121
40 129 124 118

Estimating alfalfa NDF using PEAQ with a simplified staging scale

How to use this chart

  1. Choose a representative 2-square-foot area in the field
  2. Determine the most mature stem in the 2-square-foot sampling area using the criteria shown in the table at right
  3. Measure the length of the tallest stem in the 2-square-foot area. Measure it from the soil surface (next to plant crown) to the tip of the stem (NOT to the tip of the highest leaf blade). Straighten the stem for an accurate measure of its length. The tallest stem may not be the most mature stem.
  4. Based on the most mature stem and length of the tallest stem, use the chart at the right to determine estimated NDF content of the standing alfalfa forage.
  5. Repeat steps 1 to 4 in four or five representative areas across the field. Sample more times for fields larger than 30 acres.

Note: This procedure estimates alfalfa NDF content of the standing crop. It does not account for changes in quality due to wilting, harvesting, and storage. These factors may further raise NDF content by 3 to 6 units, assuming good wilting and harvesting conditions. This procedure is most accurate for good stands of pure alfalfa with healthy growth.

Length of Tallest Stem
(from soil to stem up)
Stage of the most mature stem
 

Late Vegetative
(no buds visible on stem)

Bud Stage
(1 or more nodes with buds visible)
Flower Stage
(1 or more nodes with 1 open flower)
inches
% NDF
16 28.5 29.7 31.4
17 29.2 30.4 32.0
18 29.9 31.1 32.7
19 30.6 31.8 33.4
20 31.3 32.5 34.1
21 32.0 33.2 34.8
22 32.7 33.9 35.5
23 33.4 34.6 36.2
24 34.0 35.3 36.9
25 34.7 35.9 37.6
26 35.4 36.6 38.3
27 36.1 37.3 38.9
28 36.8 38.0 39.6
29 37.5 38.7 40.3
30 38.2 39.4 41.0
31 38.9 40.1 41.7
32 39.6 40.8 42.4
33 40.3 41.5 43.1
34 40.9 42.2 43.8
35 41.6 42.8 44.5
36 42.3 43.5 45.2
37 43.0 44.2 45.8
38 43.7 44.9 46.5
39 44.4 45.6 47.2
40 45.1 46.3 47.9
Note: Quality factors are generally expected to change each day as indicated:
RFV declines 3-4 units per day
RFQ declines 4-5 units per day
NDF declines 0.5% per day
NDFd declines 0.5% per day
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