Alfalfa Management Planning with
Growing Degree Days
Reagan Noland
M. Scott Wells
UMN Extension
Forage Team
How do we plan farm practices?
• How do we know when and how to plant,
fertilize, spray, harvest…?
• Watching the weather
• Anticipating the rate of growth and maturity
• Making assessments in the field
What do plants need in order to
grow?
• Water
• Light
• Heat
• Nutrients
• Protection
Using this info to predict growth
Water + Light + Heat + Nutrients
= Plant Growth = $/ac
• If we can assume some of these variables to
be adequate (water, light, and nutrients)…
• then we can use others (heat) to predict crop
growth.
Measuring heat units
(aka Growing Degree Days)
• How warm the average temperature is over the
minimum required for plant growth.
• For alfalfa, the average temperature needs to exceed
41 ᵒF for growth and development to occur.
𝐺𝐺𝐺𝐺𝐺𝐺𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 =
𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚 + 𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚
− 41
2
Tmax = Daily high temp (ᵒF)
Tmin = Daily low temp (ᵒF)
What are cumulative GDD?
• The sum of all GDD that have accumulated throughout the
growing season
Relative Characteristics
Predicting Alfalfa Quality with GDD
Maturity stage
Photo credit: Scott Bauer
(ASA, 2011)
Changes in NDF with GDD (Rosemount, MN)
(Noland et al., 2017)
Using cumulative GDD to plan harvest dates
• For a target 40% NDF at the first harvest, it is recommended that
alfalfa is cut at 700-750 GDD.
(Lee et al., 2010)
Resources for Retrieving GDD Info
1.
2.
3.
4.
5.
Select weather station
Navigate to Daily -> Seasonal -> GDD data
Specify base temperature
Specify date range (beginning March 1st)
Click “plot climate data” or “get tabular data”
(Midwest Regional Climate Center 2017)
1. Select Weather
Station
2. Daily Data
Seasonal
GDD
(Midwest Regional Climate Center 2017)
1. Base Temp
2. Date Range
1
2
3
(Midwest Regional Climate Center 2017)
3. Plot Data
Drag and hold mouse over figure to see GDD values on specific
days and accumulation over time.
(Midwest Regional Climate Center 2017)
Summary
• This tool is most useful for the first cut
– (when other factors are not limiting)
• GDD information (both current and historic) can be
obtained free online
• Compare records of harvest date, cumulative GDD,
and forage quality
• The 700-750 GDD guideline is a good place to start
– Remember this is for pure alfalfa stands (not mixtures)
Future Direction
• Direct measurements and destructive sampling can
help estimate quality for the second and third harvests.
– Growth staging
– PEAQ
– Scissor cut and lab analysis
• However, the application of these tools is limited by
space and time.
• Remote sensing tools are being studied at UMN to
enable quick, field-scale assessments.
(Sulc et al. 2014; Noland et al. 2015)
References
•
•
•
•
•
•
•
Schroeder, J.W. 2010. Timing is important when harvesting alfalfa as feed for dairy cows.
North Dakota State University Extension.
https://www.ag.ndsu.edu/news/newsreleases/2010/may-17-2010/harvest-alfalfa-at-right-time/
Martens, D. 2011.Central MN Alfalfa Harvest Alert May 26 Update. University of Minnesota
Extension. http://blog-crop-news.extension.umn.edu/2011/05/central-mn-alfalfa-harvest-alertmay-26.html
Midwest Regional Climate Center. 2017. Cli-MATE. http://mrcc.isws.illinois.edu/CLIMATE/
Noland, R.L., M.S. Wells, C.C. Sheaffer. 2017. Integrating canopy reflectance with
environmental factors for in-situ estimations of alfalfa nutritive value. Field Crop Res. (in
preparation)
Noland, R.L., M.S. Wells, C.C. Sheaffer. 2015. In-field predictions of alfalfa nutritive value:
Current tools and future direction. University of Minnesota Extension Forage Quarterly.
http://www.extension.umn.edu/agriculture/forages/utilization/in-field-alfalfa-qualityassessment/
Sulc, R.M, K.A. Albrecht, V.N. Owens, J.H. Cherney. 2014. Update on predicting harvest time
for alfalfa. http://fyi.uwex.edu/forage/files/2014/01/alfqualest.pdf
Lee, K., M. Allen, R. Leep. 2010. Predicting optimum time of alfalfa harvest. Michigan State
University. http://articles.extension.org/pages/25471/predicting-optimum-time-of-alfalfaharvest
Questions?