Predicting soybean [Glycine max (L.) Merr.] phenology using temperature and daylength

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Ort, Nathaniel Wesley Waldie
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Soybean [Glycine max (L.) Merr.] phenology in response to Manitoba’s (MB) environment is less understood than in long-established soybean production regions of North America like Ontario (ON) or the United States of America. The goal of this research is to fill this gap in knowledge. Soybean cultivars varying in maturity classification were grown in MB and ON from 2008 to 2010, and again in 2017 and 2018. Ontario represented a traditional short-season soybean production region of Canada, while MB represented a new, short-season prairie environment. Early maturing cultivars were selected to represent a range of maturity groups (MG) from 000 to 1.3. Dates of development stages from emergence (VE), beginning bloom (R1), beginning seed (R5) and full maturity (R8) were recorded following the Fehr et al. (1971) soybean development stage descriptions. Phenology data from the field experiments were used to develop two growth stage models, and a controlled environment experiment was conducted in growth chambers to isolate potential delaying effects long photoperiods had on time from VE to R1. In the field experiment, phenology differences between MG became prominent at R5, with later MG requiring more time than earlier MG. Soybean grown in MB spent 42 d in vegetative development and 59 d in reproductive development, while in ON soybean spent 25 and 70 d in the same development periods, respectively. In the modelling experiment, predictive equations with greatest accuracy in comparison to the growing degree day and crop heat unit were proposed as a new ‘Growth Stage Interval Unit’ (GSIU) and a ‘Photothermal Unit’ (PTU). The GSIU model was superior in growth stage predicting accuracy over the PTU; however, because the PTU is less cumbersome it is more likely to be adopted by farmers and agronomists. In the controlled environment experiment, more time was required to reach R1 under longer photoperiods for all cultivars tested, and later rated MG had greater sensitivity to photoperiod than earlier MG.
Soybean, Phenology, Plant science, Temperature, Daylength, Photoperiod, Photoperiodism, Plant growth, Plant development, Vegetative growth, Reproductive development, Soybeans