Measured Phenology Response of Unchanged Crop Varieties to Long-Term Historical Climate Change

Understanding how crop phenology responds to historical climate change is a prerequisite for evaluating crop phenology and future yield responses. Most phenology response investigations are based on the phenology observed under circumstances of varieties changing over time, which then necessitates disentangling the role of climate change from the effect of changing varieties using various models. However, results from such studies are limited by the uncertainties caused by model mechanisms and assumptions and parameter calibration and validation. In this study, phenology observations were made for varieties of winter wheat (Triticum aestivum L.), rice (Oryza sativa L.), and spring maize (Zea mays L.) at 11 agro-meteorological observation sites in north China. The varieties observed for each species did not change over a period of at least 15years. The observations were used to investigate the measured phenology response to climate. Dates of major wheat phenology stages tended to occur earlier due to warming, but the trend in rice and spring maize was not clear. Growth duration was shortened during the vegetative period of winter wheat, but was prolonged during vegetative period of rice and in the reproductive period of winter wheat and rice. Growing degree days (GDD) were generally increased for both vegetative and reproductive periods for all crops except during the vegetative period for winter wheat. We found that most trends in date of phenology stages, duration of growth phases, and GDD were similar to previous reports in which the varieties observed did not remain constant. This indicates that previous reports are likely to have overestimated the effect of cultivar shifting on crop phenology and underestimated the role of climate. Based on our results, growth duration under future warmer conditions may be longer than previously simulated, and hence yield may also be higher than previously estimated.