Simulating bimodal tall fescue growth with a degree-day-based process-oriented plant model

Authors: Kiniry, James; KIM, SUMIN - Oak Ridge Institute For Science And Education (ORISE); Williams, Amber; LOCK, THOMAS - University Of Missouri; KALLENBACH, ROBERT - University Of Missouri

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2017
Publication Date: 2/7/2018
Publication URL: http://handle.nal.usda.gov/10113/5935601
Citation: Kiniry, J.R., Kim, S., Williams, A.S., Lock, T.R., Kallenbach, R.L. 2018. Simulating bimodal tall fescue growth with a degree-day-based process-oriented plant model. Grass and Forage Science. 73:432-439. https://doi.org.10.1111/gfs.12346.
DOI: https://doi.org/10.1111/gfs.12346

Interpretive Summary: Computer models that simulate plant growth have a temperature functions driving development, with a base temperature and an optimum temperature. Such computer models often do well for plants that continuously change throughout the growing season. This becomes more complex as it is extended to cool-season perennial grasses with a dormant period and two phase growth curves. The first objective of this study was to develop a model for tall fescue for simulating such growth in the Midwest U.S. based on multiyear measurements. The functions for two-stage growth were incorporated into the ALMANAC computer model and applied to tall fescue using published USDA-NRCS tall fescue yields for a variety of sites and soils within the study region. Multiple fields each of two tall fescue cultivars were sampled weekly for dry matter accumulation over three years. These plant weight measurements were used to derive weekly growth values by differences between sequential weekly samplings. Using these results, the ALMANAC model was modified and tested against mean reported tall fescue yields for 11 sites, with one to three soils per site. When we introduced mid-summer dormancy into ALMANAC, we assumed dormancy began on the longest day of the year and lasted until the daylength was 0.68 hours shorter than the longest. ALMANAC simulated previously reported tall fescue yields well across the range of sites. Thus, ALMANAC shows great promise to simulate such two-phase growth in this common cool season grass.

Technical Abstract: Plant growth simulation models have a temperature response function driving development, with a base temperature and an optimum temperature defined. Such growth simulation models often function well when plant development rate shows a continuous change throughout the growing season. This approach becomes more complex as it is extended to cool-season perennial grasses with a dormant period and bimodal growth curves. The first objective of this study was to develop such a bimodal growth model for tall fescue (Schedonorus arundinaceus (Schreb.) Dumort) in the Midwest U.S. based on multiyear measurement trials. The functions for bimodal growth were incorporated into the ALMANAC model and applied to tall fescue using published USDA-NRCS tall fescue yields for a variety of sites and soils within the study region. Three fields each of cultivars ‘Kentucky 31’ and ‘BarOptima Plus E34’ were divided into eight paddocks (48 total paddocks), and sampled weekly for dry matter accumulation. These biomass estimates were used to derive weekly growth values by differences between sequential weekly samplings. Using these results, the ALMANAC model was modified and tested against mean reported tall fescue yields for 11 sites, with one to three soils per site. When we introduced mid-summer dormancy into ALMANAC, we assumed dormancy began on the longest day of the year and lasted until the photoperiod was 0.68 hours shorter than the longest. ALMANAC simulated previously reported tall fescue yields well across the range of sites. Thus, ALMANAC shows great promise to simulate bimodal growth in this common cool season grass.