Abstract
Identification of complete drivers for phenology changes is crucial for developing prediction models of plant phenology. In addition to climatic factors, the interaction among phenological events has recently been reported as an important driver for the phenology changes of forests, savannas, and grasslands. However, open questions remain as to whether the phenological interaction exists in agricultural ecosystems, among which winter wheat plays a vital role in feeding human beings. In this study, we investigated the interaction among the phenological events of winter wheat in the North China Plain (NCP) using both field and satellite data. Considering the large discrepancies between the existing satellite estimation and field measurements of winter wheat phenology, we first improved the MODIS-based estimation of green-up date (GUD), heading date (HD), and maturity date (MD) through a re-calibrated relative threshold method (RTM) in the NCP. The GUD, HD, and MD were accurately estimated with the mean absolute errors (MAE) and root mean squared errors (RMSE) lower than 7.5 days, compared with the RMSEs ranging from 12.0 to 36.1 days in previous studies. Then, the relationships among the GUD, HD, and MD were analyzed using the field data collected at agricultural meteorological stations. The GUD (HD) showed a significantly positive correlation with the HD (MD). Quantitatively, a one-day earlier GUD (HD) would result in an earlier HD (MD) of 0.57 days (0.60 days). Furthermore, we applied the partial correlation analysis to the improved MODIS estimation of GUD, HD, and MD to investigate their interactions by considering the simultaneous influences from climatic factors. The results showed that the HD (MD) with 85.2% (94.5%) of all winter wheat pixels presented a significantly positive correlation with the GUD (HD). Meanwhile, the GUD (HD) with 84.2% (33.3%) of the entire winter wheat area presented a significantly negative correlation with pre-season temperature. These results suggest that both the climatic factors and phenological interactions should be included in the future development of winter wheat phenology models to improve the prediction accuracies.
Highlights
Wheat is widely grown around the world as a major staple food, and feeds more than 35% of the world’s population [1]
The phenological interactions among green-up date (GUD), heading date (HD), and maturity date (MD) were investigated based on the phenological events derived from MODIS data
Validation results showed that the GUD, HD, and MD can be accurately estimated with the mean absolute error (MAE) and root mean squared error (RMSE) ranging from 2.9 to 7.5 days
Summary
Wheat is widely grown around the world as a major staple food, and feeds more than 35% of the world’s population [1]. The NCP has been encountering severe shortages of water resources in recent decades, which has become the largest risk for the agricultural sustainability of the NCP, threatening its reliable contributions to guaranteed food security in China [3,4]. To facilitate the water resource management and yield estimation of winter wheat in the NCP, the observations and models of winter wheat phenology are extensively required [5]. Measurements of the key phenological events, including green-up date (GUD), heading date (HD), and maturity date (MD), are necessary for computing the water demand of winter wheat throughout the growing season [6]. The phenology models are essential for predicting the responses and feedbacks of winter wheat to future climate change, and for analyzing the changes of its water demands under different simulation scenarios of management strategies [7]
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