Alfalfa stands in the local area had a slow start this spring, but our recent wet weather is causing alfalfa development to move quickly. The biggest problem farmers are facing is trying to harvest the hay before it becomes to mature.
It is common for many growers to base harvest decisions primarily on alfalfa maturity; however, variable weather conditions affect the rate of bud and flower development in alfalfa and this method can be inaccurate. Often under cool spring conditions, the alfalfa crop does not develop buds and flowers as normal, yet fiber continues to accumulate. In contrast, under hotter and drier conditions, blooming alfalfa may still be of high quality.
Factors that reduce growth often result in a fine-stemmed, leafy plant that is high in quality. Examples include cool temperatures, heavy or salty soil, moderate moisture stress, and deficiencies of some nutrients. Conversely, factors that hasten maturity, cause leaf loss or result in thin stands allowing weeds to invade, generally reduce forage quality. These factors include high temperatures, severe moisture stress, and many pests such as nematodes, diseases and insects.
Estimating fiber content before harvest can be valuable to producers for making harvest timing and storage decisions. Traditional laboratory methods for estimating forage fiber content are often expensive and time consuming and are not practical as a tool for making harvest-timing decisions in the field.
A method developed years ago using alfalfa maturity and height still provides an accurate guide for making harvest timing decisions by estimating neutral detergent fiber (NDF) of the standing crop. This method uses height and maturity stage to estimate NDF in pure alfalfa stands.
Step 1: Choose a representative 2-square-ft area in the field to be harvested.
Step 2: Determine the most mature stem in the 2-square-ft sampling area. Vegetative = no buds or flowers present; Bud = one or more nodes with buds; flower = one or more nodes with open flowers.
Step 3: Measure the length of the tallest stem in the 2-square-ft 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.
Step 4: Based on the most mature stem and length of the tallest stem, use the chart to determine estimated NDF of the standing alfalfa forage.
Example: tallest stem is 28 inches, most mature stem has buds, but no open flowers; NDF = 38.0.
Step 5: Repeat steps 1-4 in five representative areas across the field. Sample more in fields larger than 30 acres. Average all estimates for a field average.
Using this system, the estimated NDF was within three units of the wet chemistry NDF for 77% of more than 500 samples tested. This method was consistent across a wide range of environments and can be used during the entire growing season, not just on the first crop. Therefore, it provides a reasonably accurate guide for timing alfalfa harvests according to your forage quality goals all season long. It works only in pure stands of alfalfa and is most accurate under normal growing conditions.
NOTE: This estimates alfalfa NDF of the standing crop. It does not account for changes in quality from wilting, harvesting, and storage, which may further raise NDF 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.
Source: Estimating Alfalfa Fiber Content in the Field, by R. Mark Sulc – Department of Horticulture & Crop Science