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Using growing degree days to plan early-season alfalfa harvests

Purple alfalfa flowers

When spring approaches, alfalfa growers need a plan for optimizing the first harvest’s nutritive value and yield. Here, you'll find strategies for making in-field predictions of alfalfa nutritive value, and when and how they should be used.

Some crop growth predictions are based on environmental information, while others are based on directly measuring the crop in the field. Tracking the accumulation of growing degree days (GDD) is a common approach for estimating the crop’s growth and maturity in the field based on actual temperature conditions rather than calendar days.

Understanding growing degree days (GDD)

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Planning the first cut

In the upper Midwest, it’s generally recommended to plan the first cut near the accumulation of 700 to 750 GDD.

This is intended to achieve a neutral detergent fiber (NDF) concentration near 35 percent at harvest, resulting in NDF concentrations near 40 percent – with a relative feed value (RFV) of approximately 150 – when used as feed or sold as hay.

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Reagan L. Noland, graduate student, College of Food, Agricultural and Natural Resource Sciences and M. Scott Wells, Extension agronomist

Reviewed in 2018

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