Forecasting the soybean phenophases onset dates in the Primorsky Region under climate change

The objective of the study is to model and forecast the dynamics of soybean development in the Primorsky Region under climate change conditions. The material for the study was phenological observations in 1990–2021 for three soybean varieties (Primorskaya 529, Hodson, and Venera) at the Far Eastern Experimental Station, a branch of VIR. The dates of the beginning and full germination, beginning and full flowering, beginning and full ripening were studied. The dependence of the onset of these phenophases on monthly temperatures, precipitation amounts, and dates of temperature transition above 10, 11, …, 19, 20 °C was studied. In 1990–2021, an increase in summer temperatures was observed while the precipitation level remained the same and there was a tendency for all three soybean varieties to ripen earlier by 0.16–0.18 days/year. Regression analysis showed that the dates of the beginning of flowering, the beginning and full ripening of soybeans in the conditions of heat supply deficit in the Primorsky Region were more than 50 % regulated by temperature. A strong dependence of the beginning date of flowering of the "medium variety" of soybeans on the date of transition of temperature above 18 °C (D18), r = 0.82, was revealed. It can be assumed that this is the minimum temperature for flowering of varieties adapted to the conditions of the Primorsky Region. The rate of development of soybean plants after flowering was determined to a large extent by endogenous factors, as shown by strong correlations between the date of the onset of ripening and the date of the onset of flowering (r = 0.82) and full ripening and the onset of ripening (r = 0.79). The dates of the onset and full ripening also correlated with the dates of the transition above 17–18 °C (r = 0.69–0.72) for all varieties. An earlier transition of temperature above 18 °C by 1 day causes an acceleration of flowering by an average of 0.4 days and an acceleration of ripening by 0.2 days. If the observed trends in agroclimatic indicators are maintained, it is possible to predict a continuation of the shift in soybean flowering and ripening to earlier dates at a rate of 0.1 days/year, or 1 day/10 years.