Variability of soybean yield and seed quality depending on environmental hydrothermal factors
Authors: Ryabukha S. S. , Chernyshenko P. V. , Bezuglyi I. M. , Kobyzeva L. N. , Kolomatska V. P. , Golokhorynska M. G. 
Published: May 2023

Purpose and objectives. Our purpose was to establish patterns of influence of the hydrothermal mode on the soybean yield and seed quality in the Eastern Forest-Steppe of Ukraine and to determine the variability of traits under the influence of environmental factors.
Materials and methods. Varieties and breeding accessions of the 2008–2018 competitive variety trials in the amount of 60 to 153 were taken as the test material. Soybeans were grown in compliance with the technology typical for the study location in four replications; the plot area was 25 m2. The dependence of variability of yield and quality on the hydrothermal environmental factors was determined by correlation analysis and mathematical modeling.
Results and discussion. During the growing period, the soybean yield was most closely correlated with relative air humidity (r = 0.712) and precipitation amount (r = 0.468). There was an insignificant negative correlation between yield and average air temperature (r = -0.266). The yield was not correlated with the sum of effective temperatures (r = 0.081). The lowest yield (0.40-0.60 t/ha) was observed at the maximum values of average air temperature (20.0oC) and air relative humidity (52%). When the relative air humidity rose to 64% at the maximum temperature, the yield increased to 1.40-1.60 t/ha. At the minimum relative air humidity, a rise in temperature significantly reduced the yield: from 1.40-1.60 t/ha to 0.40-0.60 t/ha. The highest yield, according to the mathematical model, was achieved by combining moderate temperature (18.0–18.5oC) and high relative air humidity (64%). The seed yield determined the output of protein and oil from 1 ha (r = 0.994), had no significant relationship with protein content (insignificant r = -0.106) and was weakly negatively correlated with oil content (r = -0.220) and the total content of protein and oil (r = -0.192). There was a moderate negative correlation (r = -0.403) between protein and oil contents. The total content of protein and oil in seeds was determined by protein content (r = 0.948) and did not depend on oil content (r = -0.091). The protein content was moderately negatively correlated with relative humidity (r = -0.582) and average air temperature (r = -0.437) and weakly correlated with precipitation amount (r = -0.213). The oil content in seeds was positively correlated with the average temperature during the growing period (r = 0.435) and relative air humidity (r = 0.376). The output of protein and oil did not depend on protein content (insignificant r = -0.006) and was negatively correlated with oil content (r = -0.223). The total content of protein and oil in seeds was negatively affected by relative humidity (r = -0.502), average air temperature (r = -0.325), and precipitation amount (r = -0.175). The output of protein and oil, like yield, was positively correlated with wetting factors (relative air humidity (r = 0.686) and precipitation amount (r = 0.603)) and negatively correlated with thermal factors (average air temperature (r = -0.706) and the sum of effective temperatures (r = -0.362)). There were some differences in the correlations between the environmental factors during the entire growing period and the economic characteristics and between the environmental factors separately during the first (April-June) and second (July-September) halves of the soybean growing period and the economic features.
Conclusions. We demonstrated a leading role of relative air humidity for soybean yield (r = 0.723). The dependence of yield on precipitation amount during the growing period was moderate (r = 0.605). The role of precipitation increased in the first half of the growing period (r = 0.525) compared to the second half (r = 0.342). There was a moderate negative correlation between yield and average air temperature (r= -0.666) as well as between yield and the sum of effective temperatures during the growing period (r = -0.373). There was a moderate negative correlation (r = -0.403) between the contents of protein and oil. The total content of protein and oil in seeds was determined by protein content (r = 0.948) and did not depend on oil content (r = -0.091). The protein content was moderately negatively correlated with relative air humidity (r = -0.582) and average air temperature (r = -0.437) and weakly correlated with precipitation amount (r = -0.213). The oil content in seeds was positively correlated with the average temperature during the growing period (r = 0.435) and relative air humidity (r = 0.376). The output of protein and oil did not depend on protein content (insignificant r = -0.006) and was negatively correlated with oil content (r = -0.223). The total content of protein and oil in seeds was negatively affected by relative humidity (r = -0.502), average air temperature (r = -0.325), and precipitation amount (r = -0.175). The output of protein and oil was positively correlated with relative air humidity (r = 0.686) and precipitation amount (r = 0.603) and negatively correlated with the average air temperature (r = -0.706) and effective temperature sum (r = -0.362). A mathematical model of the dependence of soybean yield on the hydrothermal factors was constructed.