Alfalfa harvest likely delayed by up to 1-2 weeks in Michigan
By the end of April 2013, all of Michigan had fallen behind normal temperatures for growing degree day accumulation. This will likely result in slow alfalfa growth and later than normal first harvest.
The cold start to the 2013 spring is resulting in lower than normal values for Growing Degree Days (GDD) in Michigan. GDD are a measure of heat unit accumulation. Because early season growth of alfalfa is related to the sum of heat units accumulated, monitoring GDD is an easy and effective way to determine when to harvest to optimize forage quality of first cutting alfalfa. Michigan State University Extension recommends that dairy hay should be harvested at The mid-bud stage of growth which will normally provide 40 percent Neutral Detergent Fiber (NDF) to maximize the yield and quality of feed to lactating dairy cows. Delaying harvest after the recommended harvest time of 40 percent NDF will result in higher yields, higher fiber, lower NDF digestibility and lower protein. Harvest of dairy quality alfalfa that will be stored in horizontal bunkers should begin at 680 GDD. Haylage that will be stored in a vertical silo can be harvested at 750 GDD.
For alfalfa, GDD is based on the minimum and maximum daily temperatures beginning March 1, using a base of 41 degrees F. The daily calculation is [(maximum temp + minimum temp)/2] - 41. The GDD accumulation is the sum of the daily GDD values across days beginning March 1. Producers can get a good idea of how the season is progressing by comparing accumulated GDD to previous seasons.
As of April 28, 2013 all of Michigan was behind normal (1980-2007) for growing degree accumulation. The majority of lower Michigan is more than 14 days behind in heat accumulation, while a few areas in the Thumb and Upper Peninsula are 1 - 2 weeks behind and a very small area in the Upper Peninsula is only 3 days to 1 week behind. Warmer than normal weather is soon forecasted which will cause GDD to rise rapidly, but harvest will likely still be delayed. It is important to keep close track of the GDD as we progress this spring.
It is important to monitor alfalfa growth in growing seasons that are atypical so that forage yield and quality are maximized for the dairy herd. Tracking GDD or taking measurements using a PEAQ (predictive equations for alfalfa quality) stick will result in better quality feed than by going from previous calendar dates of when alfalfa is typically ready for harvest. With hay inventories short after the drought of 2012, it may be tempting to take hay early, but it will pay in the long run to wait until the GDD indicate it is the proper time to harvest.