Reevaluation of the degree day base 60°F concept in US cotton (Gossypium hirsutum L.) production

Abstract

AbstractCotton (Gossypium hirsutum L.) management decisions to abet early growth, fruit set, boll maturation, and harvest preparation are often facilitated by prediction of the date when critical developmental stages are reached. In the United States, growing degree days calculated with a base 60°F (DD60s) are commonly used to predict cotton development. Observations suggest development of modern cultivars differs from previously established guidelines. The objectives were to (1) reevaluate DD60s required for an early, mid‐maturing and late maturing cultivar to reach key growth stages across the US Cotton Belt; and (2) determine if predictions of growth stages are strengthened by optimizing base temperature or including an upper threshold by growth stage. During 2018 and 2019, 22 field trials were established in 10 states. Plant growth stages were monitored weekly and air temperature was computed from interpolated surface observations weighted by a physical, geographic model. Observed DD60s to reach growth stages varied slightly by cultivar and region (≤85 DD60s and ≤130 DD60s, respectively). Required DD60s to reach growth stages exceeded most published ranges. Optimization of base temperature and inclusion of an upper threshold by growth stage did not substantially decrease errors in predicting date of growth stage occurrence. The DD55 and DD55 with an upper threshold of 86°F calculations resulted in slightly lower errors in predicting date of growth stage occurrence than the DD60 calculation. Although guidelines should be updated, it is unlikely slight modification in base temperature or upper thresholds will drastically increase the predictive ability over the DD60 calculation.