Winter Wheat Phenology
Phenology Maps: 1982 - 2020
Maps displaying the calculated jointing, heading and physiological maturity dates based on observed planting and harvest dates for each study counties in winter wheat belt between 1982 and 2020. Phenology Maps
The phenological observations (sowing and harvest dates) were derived from 243 experimental stations of winter wheat performance test across South Dakota (SD), Nebraska (NE), Colorado (CO), Kansas (KS), Oklahoma (OK), and Texas (TX) over 1982-2020, and then interpolated with a Delaunay Triangulation (Barber et al., 1996) to the centroid of each county.
Due to missing data in some years, we developed a linear model using near-complete data across KS and NE as dependent variables based on the leave-one-out approach (overall, the goodness of fit (R2) is more than 0.5), the fitted model then was used to predict planting/harvest dates for missing years. Consequently, we derived the complete phenological data for planting and harvest dates for each county from 1982 to 2020. Note that harvest date was not recorded in TX.
Next, based on an empirical relationship between maturity and harvest dates that the maturity occurred approximately 2 weeks prior to harvest, we derived the physiological maturity of winter wheat (Robertson et al., 2004). Although missed harvest date for TX, the observed heading dates covered three counties (Bushland, Chillicothe, and Dallas) over 20 years were available recorded by Agricultural research service US department of Agriculture.
Growing degree days (GDD) is a common matrix used to predict maturity date of winter wheat in Great Plains (Peairs and Armenta., 2010). For example, the jointing and heading dates were defined as reaching 35% and 57% of GDD from January 1 to maturity date, respectively. In addition, the maturity date for each county-year in TX was also identified via calculating the average GDD of reaching maturity across the three counties based on this ratio (57%). This method was also applied in phenology estimation of corn in US corn belt (Sacks, et al., 2011).
Therefore, we partitioned three phenological stages including planting to jointing (PT-JT), jointing to heading (JT-HD), and heading to maturity (HD-MT) in this study.
Peairs, F., and R. Armenta, Eds., 2010: Wheat Production and Pest Management for the Great Plains Region. Colorado State University Extension, 188 pp.
Sacks WJ, Kucharik CJ (2011) Crop management and phenology trends in the U.S. Corn Belt: impacts on yields, evapotranspiration and energy balance. Agricultural and Forest Meteorology, 151, 882– 894.