Estimation and evaluation of winter wheat phenology in the central Great Plains

Abstract

Crop modeling and management requires accurate prediction of crop phenology. Phenology data for winter wheat ( Triticum aestivum L.) were collected from seven sites in the central Great Plains for several years to relate phenological stages to environmental and cultural factors, and to provide needed phenology data for the central Great Plains. Number of calendar days ( ND), growing degree-days ( GDD), and photothermal units ( PTU) were calculated for emergence (E), tiller initiation (TI), dormancy end (DE), jointing (J), heading (H), kernel in milk (KM), kernel in hard dough (KD), and maturity (M) using the Feekes growth scale for the main stem. Nine base temperatures (−2, 0, 1, 2, 3, 4, 5, 7, and 9°C) were used when accumulating GDD and PTU. Mean daily temperatures of 20, 25, and 30°C were used for upper thresholds. Accumulation of GDD, PTU and ND were calculated from planting date (S), E, and 1 January to the growth stage and from one growth stage to the next. Model sensitivity to soil water, cultivar, seeding rates, row spacing, rotation, and fertilizer were examined. The lower the base temperature for a model, the lower the root mean square error ( RMSE) when beginning accumulation from S, E or 1 January, with −2°C the best except for DE, KD, and M where higher base temperatures tended to have lower RMSE. As M was approached, the 25°C upper threshold tended to do better than 20°C. Little difference was found between 25 and 30°C upper thresholds. The best model for predicting a stage varied, with ND the best for E through J. From H through M, PTU models had the lowest RMSE. Normally, GDD and PTU models beginning accumulation from 1 January outperformed models beginning accumulation from S or E. The GDD or PTU related to availability of soil water showed a parabolic relationship (concave downward) beginning at J and becoming more platykurtic as M was approached. Significant sensitivity to cultivar and row spacing/rotation was found, with occasional sensitivity by various model types found to fertilizer and planting date.