|Camp Jr, Carl|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2000
Publication Date: N/A
Interpretive Summary: Periods of inadequate rainfall in the southeastern Coastal Plain cause drought stress in soybean, which reduces yields most years. A better understanding of the way that drought stress affects soybean yield would help in the development of improved cultivars and better production systems to reduce the effects of drought. In this field experiment, soybean seed yield was measured separately for various parts of the plant (main stem an branches). A range of drought conditions was provided by combinations of deep tillage (access to more stored water) and irrigation. Irrigation increased soybean seed number and weight on branches but not on the main stem, which means that vegetative development of branches is necessary for high soybean yield. Prevention of drought stress during critical periods of the growing season can increase soybean yield in this region. Development of cultivars for rainfed production systems may be enhanced by selecting plants with a higher ratio of yield on the main stem rather than branches. This work is important to scientists developing improved soybean cultivars.
Technical Abstract: Soybean [Glycine max (L.) Merr.] seed yields are substantially reduced by drought stress most years on the southeastern Coastal Plain. A better understanding of how drought stress affects soybean seed-yield determination would aid in the development of improved cultivars for this region and better production systems aimed at ameliorating the effects of drought stress. The objectives of this field study were to examine the effects of drought stress on soybean branch vegetative growth, branch seed yield, and total seed yield and to determine how drought stress affects the distribution of seed yield and yield components between the main stem and branch fractions. Soybean was grown in 1998 and 1999 on an Eunola loamy sand with treatments of irrigation and no deep tillage, deep tillage but no irrigation, and no deep tillage or irrigation. Total seed yield and the percentage of total seed yield on branches were highest with irrigation, followed by the deep tilled/no irrigation and the no deep tillage/no irrigation treatments. Irrigation had no effect on mainstem seed yield, but increased branch seed yield by an average of 107%, compared to the no deep tillage/no irrigation treatment. On a unit area basis, branch seed number was highly correlated with branch seed yield and total seed yield over both years and all levels of soil water treatment. Also, branch seed number was closely related to branch dry weight at harvest maturity, final branch length, and final branch number. Most branch growth occurred between initial flowering and the beginning of seed fill. These data indicate that drought stress occurring between initial flowering and early seed fill decreases total seed yield primarily by reducing branch vegetative growth, which reduces branch seed number and branch seed yield.