The growth stages of the alfalfa plant from germination to full maturity are shown in Figure 1 and Figure 2. The first leaf of the alfalfa plant is unifoliate (a single leaf) occurring above the cotyledons. Subsequent leaves are trifoliate (three leaflets per stem) or multifoliate (more than three leaflets per stem), depending on the variety. These leaves are on alternate sides along the stem. Stems produced after the first (primary) stem are called secondary stems.
Crown development, also called contractile growth, begins about 1 week after emergence. This growth process may last up to 16 weeks. The cells in the stem below the cotyledonary node become shorter and thicker to form the crown. This process sometimes pulls the cotyledon and unifoliate below ground. Varieties with lower fall dormancy rating tend to express more contractile growth.
Root nodulation occurs within 4 weeks of germination, provided enough viable rhizobia are present around the seed.
Mean Stage by Count
Sample at least 40 stems from five or six locations in the field that are representative of growing conditions across the field. Reference Figure 1 and Figure 2 to sort stems by developmental stage. Count the number of stems at each stage. The Mean Stage by Count method relies on a weighted average, so multiply the number of stems at each stage by the stage number. Add these up and divide by the number of stems (Mueller and Teuber, 2007).
Mean Stage by Weight
Sample at least 40 stems from five or six locations in the field that are representative of growing conditions across the field. Reference Figure 1 and Figure 2 above to sort stems by developmental stage. Dry the stems in an oven at 60°C and weigh them. Mean Stage by Weight is calculated the same way as Mean Stage by Count, except that the weight of stems at each stage is used instead of the number of stems (Mueller and Teuber, 2007).
References
Mueller and Teuber, 2007. Alfalfa Growth and Development [Chapter]. In Irrigated Alfalfa Management for Mediterranean and Desert Zones.