Brian Lang, ISU Extension field agronomist
The exceptionally warm spring has alfalfa growth well ahead of normal, with some farmers expecting to harvest first crop in April. Those that normally harvest first crop alfalfa by calendar date, often harvest in mid to late May. Harvest should be much sooner this spring, but when? Consider using the Predictive Equations of Alfalfa Quality (PEAQ) to determine when to harvest. PEAQ is a simple management tool to estimate alfalfa quality in the field to help predict the best time to harvest first crop.
PEAQ provides an estimate of alfalfa quality based on stage of plant development and stem height. This allows you to estimate standing crop forage quality with a yard stick and your observation of the stands stage of development; vegetative, bud or bloom. Just use these two factors with Table 1 in the PEAQ fact sheet to estimate relative feed value (RFV). Under the best harvest conditions, 10 to 20 percent of the forage dry matter will be lost at harvest. This amounts to approximately 15 RFV points for haylage and 25 RFV points for hay. Therefore, if you are trying to end up with 150 RFV alfalfa, you should consider harvesting the crop when PEAQ measurements estimate a RFV of 165 to 175 for the standing alfalfa crop in the field.
To help monitor the progress of alfalfa stands in Iowa, Extension created a PEAQ website where RFV determined by PEAQ are posted for various alfalfa fields across Iowa. To see these postings, go to PEAQ and click on "All Above Counties" in the lower right of the Web page. However, these postings are no substitute for monitoring your own fields. As you see in these postings, there are considerable differences from field to field, as expected, do to field location in the state, variety, harvest management, soil fertility, soil type and other factors that affect alfalfa growth and development.
Brian Lang is an Iowa State University Extension field agronomist serving northeastern Iowa. He can be reached at 563-382-2949 or firstname.lastname@example.org.