Estimating Pre-Harvest Alfalfa NDF in the Field

Alfalfa neutral detergent fiber (NDF) concentration can be estimated in the field before harvest by following a simple procedure while walking across the field:

1. Choose a representative 2-square foot area in the field.
2. Determine the most mature stem in the sample area:
   
   • Vegetative = no buds or flowers are visible;
   • Bud = 1 or 2 nodes with buds visible;
   • Flower = 1 or more nodes with open flowers.
3. Measure the length of the tallest stem in the sample area. Measure it from the soil surface to the tip of the stem (not the leaf tip, but the stem tip). Straighten the stem to its full length when measuring. The tallest stem may not be the most mature stem you find.
4. Based on the stage of the most mature stem and length of the tallest stem, read the estimated NDF from the table below. For example, if the most mature stem has buds but no flowers and the tallest stem is 28 inches, then NDF = 38.0.
5. Repeat steps 1 to 4 in several representative areas of the field and calculate the average value. More estimates gives a better overall average.

Note: This estimates the NDF of the standing crop and does not account for changes in fiber due to wilting, harvesting, and storage, all of which can raise the NDF by 3 to 6 units, assuming good wilting and harvesting conditions.

Estimated Pre-Harvest Alfalfa NDF

Length of tallest stem	Vegetative	Bud Stage	Flower Stage
(inches)	% NDF	% NDF	% 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