An important IPM strategy is to choose fields that are well suited to alfalfa production. A field's cropping history is important; alfalfa planted in fields with poor drainage, poor nutrient balance, or infested with alfalfa pests, especially weeds, will suffer yield loss and greater pest problems.
Identify the crops and vegetation surrounding your alfalfa fields and determine pest history for those fields. For example, check to see if they harbor pathogens (such as Sclerotinia) or have a history of nematodes. Carefully planned cultural practices, including early fall planting dates, can help manage pests, including insects, weeds, and diseases.
Key Issues for Site Selection
Proper drainage is critical for the development of a healthy root system. If drainage is poor, consider physical modification such as deep tillage, raised beds, or installation of drainage tiles.
Alfalfa grows successfully on a wide range of soil textures, but sandy loam to clay-loam soils are preferred.
A site should provide a minimum of 3 feet of unrestricted rooting depth.
Water Holding Capacity
High water-holding capacity is desired, but with good drainage.
Soil pH, Soil Fertility
Near neutral pH is highly preferred. Low pH soils cause problems with nodulation with Rhizobium bacteria and nitrogen fixation, while high pH soils may have limitations for nutrient availability and salinity or sodicity issues. A pH of 6.4 to 7.5 is recommended.
Check for excess boron, selenium, or sodium.
Water Supply, Water Quality, and Irrigation System
Sufficient supplies of adequate quality water are required for successful production. Established alfalfa is tolerant of moderately saline water and high nitrate wastewater. Choose an appropriate irrigation system for site (sprinkler, flood or drip)
Highly variable fields with high and low spots may require land leveling, depending upon irrigation system.
Alfalfa is somewhat tolerant of saline soils and water, but salinity can reduce stand establishment and growth, and encourage weed intrusion. Alfalfa can tolerate salinity levels up to 5 dS/L, but care should be taken to manage saline soils and water, especially during stand establishment. On very saline soils, mitigate salinity over time by growing other crops (e.g. barley) and leaching salts.
Do not plant alfalfa after alfalfa; rotate to another crop for at least 1 to 2 years between alfalfa plantings. This is important to manage residual disease, weed, nematode, and rodent problems. Rotate with non-legume crops (i.e., corn, cereals, cotton, tomato).
If high numbers of difficult-to-control weeds are present, avoid the field and develop a strategy for control before planting.
If diseases are known for a region, be sure to select appropriate disease-resistant varieties.
If field has a history of nematodes that attack alfalfa, select varieties rated as highly resistant, consider crop rotations, or avoid using the field for alfalfa.
If weevils, aphids, cutworms, or armyworms are known for and area, develop an IPM strategy for control.
For more information on site selection, see Irrigated Alfalfa Management for Mediterranean and Desert Zones, UC ANR Publication 3512.