Phenological responses of old and modern soybean cultivars to air temperature and soil moisture treatment

Abstract

Soil moisture deficits and low air temperatures frequently result in crop yield losses in the United States. Understanding how older and newer soybean ( Glycine max (L.) Merr.) cultivars differ in phenological development under various environmental conditions may aid in the selection of higher-yielding cultivars and in the development of simulation models for field-grown soybean. In this study, we examined the phenological responses of two widely adapted older (‘Dunfied’ and ‘Manchu’) and two more-recent (‘Clark 63’ and ‘Williams 82’) soybean cultivars to soil moisture deficit and monitored the development of these cultivars as a function of air temperature. These cultivars were grown under drought stress and irrigation on a Flanagan silt loam soil at Urbana, Illinois, in 1984 and 1985. The soil moisture-deficit treatment was begun approximately 2 weeks before initial flowering (R1 stage) and was continued until harvest maturity. Drought stress reduced the final number of mainstem nodes due to a decrease in the rate at which the nodes were produced, but had little effect on the date of termination of node formation. Except for Manchu, no association was observed between the number of nodes produced under irrigation and the magnitude of the decrease in node number due to drought stress. Although the correlation between cumulative growing degree-days and mainstem node formation was high, little difference was found between the old and modern cultivars in their responses to air temperature. A period of low temperatures during early flower formation in 1985 appeared to have partially contributed to a delay in flower appearance of each cultivar. The results from this study show that the old and modern cultivars do not differ in their phenological responses to drought stress.