AMES, Iowa – Relying on calendar date is not the best way to determine when to harvest the first alfalfa crop of the season, due to climatic variations impacting alfalfa growth and development.
A better way to make harvest decisions is the PEAQ method (Predictive Equations for Alfalfa Quality)which takes climate variations into account to roughly estimate the relative feed value (RFV) of standing alfalfa in the field.
“This system provides a quick and easy ballpark estimate of forage quality,” said Brian Lang, field agronomist with Iowa State University Extension and Outreach. “Planning harvest of alfalfa by calendar date doesn’t work to determine forage quality. Instead farmers should pay attention to plant height and maturity to estimate the crop’s relative feed value.”
ISU Extension and Outreach is monitoring alfalfa fields across Iowa using PEAQ and posts readings online. Obviously farmers monitoring their fields in southern Iowa will reach their target RFV values earlier than those in northern Iowa. But fields in the same region can also show different PEAQ readings relative to variety and response to last season’s management.
“We are trying to create awareness of the growing conditions across the state,” Lang said. “We really want farmers to check their own fields. Even on their own farm they might have three alfalfa fields that will measure differently. This approach helps them know what field to harvest first and when they might want to start that harvest relative to their forage quality needs.”
There is a fact sheet that instructs farmers how to use PEAQ in their own fields. A critical step with the PEAQ method is to understand that readings from the field represent standing crop quality and that those readings need to be adjusted to account for harvest losses. Harvest losses equal about 15 RFV units for haylage and about 25 RFV units for hay. Therefore, if the target for harvest is 150 RFV alfalfa, it is recommended to harvest haylage when PEAQ measurements predict about 165 RFV for haylage and 175 RFV for hay.