Alfalfa, known scientifically as Medicago sativa, is a perennial legume widely valued for its high-quality forage and its benefits as a cover crop. This plant is a powerhouse of nutrition for livestock, often harvested as hay, silage, or grazed, due to its high protein and mineral content. Alfalfa engages in a symbiotic relationship with Rhizobium meliloti bacteria, which form root nodules that fix atmospheric nitrogen. This natural nitrogen fixation significantly enhances soil fertility, making the crop highly desirable for sustainable agricultural systems.
Site Selection and Soil Preparation
Alfalfa thrives in deep, well-drained soils, ideally with a sandy loam, silt loam, or clay loam texture, as it cannot tolerate waterlogged conditions. The plant develops a long, aggressive taproot, which can extend 6 to 12 feet or more in optimal conditions, necessitating a minimum of 3 feet of unrestricted rooting depth for high yield potential. Soil chemistry is equally important, as alfalfa requires a high pH level, with a target range of 6.5 to 7.5, because the nitrogen-fixing bacteria are most active in this slightly alkaline environment.
Soil testing should be conducted six to twelve months prior to planting to accurately determine pH and nutrient levels for phosphorus and potassium, which are heavily utilized by the crop. If the pH is too low, agricultural lime must be applied and thoroughly incorporated into the topsoil, as this process takes significant time to neutralize soil acidity. The seedbed must be firm and fine-textured to ensure close seed-to-soil contact, crucial for rapid germination and emergence. Before planting, eliminate all perennial weeds and check for herbicide carryover, as alfalfa seedlings are poor competitors during establishment.
Optimal Sowing Techniques and Timing
The physical act of planting requires precision, as alfalfa seeds are small and easily planted too deep, which prevents the seedling from reaching the soil surface. The recommended planting depth is shallow, generally between 1/4 and 1/2 inch in medium-to-fine textured soils, increasing slightly to about 3/4 inch in sandy soils. The most reliable method for achieving this consistent depth is using a drill with depth control mechanisms and packer wheels.
Alfalfa has two primary optimal seeding windows: early spring and late summer. Spring planting allows the seedlings to benefit from adequate moisture and cool temperatures, though it can lead to increased competition from summer annual weeds. Late summer planting, typically from mid-July through August depending on the region, is often preferred because it reduces weed pressure, but it requires sufficient soil moisture for establishment before the first killing frost. Regardless of the timing, the seed must be inoculated with the specific Rhizobium meliloti bacteria just before planting to ensure effective nitrogen fixation; while many commercial seeds are pre-inoculated, a fresh application is often recommended.
Ongoing Maintenance and Protection
Once established, the focus shifts to maintaining stand health through proper water management and pest monitoring. Although alfalfa is relatively drought-tolerant due to its deep root system, it requires substantial water to maximize its yield potential, especially during the peak summer growing season. Irrigation should aim for deep watering to replenish the soil moisture in the entire root zone, often 4 to 6 feet deep, allowing the plant to draw on these reserves during dry periods. Watering frequency will vary based on soil type, but established stands typically require multiple deep irrigations per month during active growth.
Weed control is significant, particularly in the first year when seedlings are vulnerable to aggressive weeds. Established alfalfa can suppress many weeds once a dense canopy forms, but weeds like bluegrass can be persistent and require careful management. Monitoring for insect pests is equally important, as several species rapidly reduce yield and forage quality. Common pests include the alfalfa weevil, which feeds on buds and leaves, and various species of aphids that suck plant sap and inject toxins. Regular scouting, often using a sweep net, helps determine if pest populations have reached levels requiring intervention.
Harvesting and Utilization
The timing of the first cutting is a balance between maximizing forage quality and ensuring the plant has stored enough root carbohydrates for vigorous regrowth and winter survival. Maximum forage quality is achieved when the plant is in the late bud stage, just before the first flowers appear, or before 10% of the stems have begun to bloom. Harvesting at this stage ensures the highest crude protein and digestibility levels in the resulting hay or silage.
The height at which the crop is cut is a determining factor in stand persistence and regrowth capacity. Leaving sufficient stubble, typically 2 to 3 inches, is recommended to protect the crown and allow for rapid initiation of the next growth cycle. Alfalfa is primarily used as high-quality forage for dairy and beef cattle, but it is also utilized as silage or as a green manure crop to enrich the soil before planting non-legume crops.