Cold units and their relationship with wheat grain yield in the Yaqui Valley, Sonora, Mexico

Global warming has the potential to cause the reduction of the cold period available during the winter, which may affect the production of wheat and deciduous fruit trees. Wheat requires accumulated cold units (CU) to switch from a vegetative period to a productive one, making the phenological cycle slower and promoting greater productive yield. The objective was to analyze the accumulation of CU and wheat yield during the last five fall-winter agricultural seasons (2018-2019 to 2022-2023) in the Yaqui Valley, Sonora, Mexico. Data of air temperature were obtained from 21 meteorological stations from the network of automatic meteorological stations of the state of Sonora, located in the Yaqui Valley. The number of CU (≤ 10 °C) was calculated for the wheat season (November 15 to April 30) from the years 2018 to 2023, and the grain yield was obtained from the reports by the Agri-Food and Fisheries Information Service. Descriptive statistics of central tendency, dispersion and the Shapiro-Wilk test were performed to determine the normality of the data; also, correlation analysis and the simple linear regression model by least squares were performed. The 2022-23 crop season showed the highest average grain yield (7.79 t ha-1) and the highest average number of CU (882) among the five seasons analyzed. Wheat seasons 2018-2019 and 2019-2020 had an average number of CU lower than 500. The Pearson correlation analysis showed a highly positive correspondence between CU and grain yield. The linear regression model showed that starting from a base of 434 CU, wheat production per hectare would be 5.90 t, and it will increase 214.3 kg for every additional 100 CU.