Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2000
Publication Date: N/A
Interpretive Summary: A major advantage of soybean in U.S. agriculture is that it does not require the application of large amounts of nitrogen fertilizer because it has the ability to fix atmospheric nitrogen for direct use by the crop. It has been found, however, that this fixation process is very sensitive to soil drying and that the nitrogen fixation capability is inhibited to some extent in virtually every cropping season. This research, done in cooperation with ARS scientists at Gainesville, FL and Urbana, IL, was undertaken to identify soybean cultivars that have nitrogen fixation that is less sensitive to soil drying. In a unique three-stage study involving more than 3000 cultivars, eight cultivars were identified with considerable nitrogen fixation tolerance to drought. These eight lines will be used in soybean breeding programs to develop improved commercial varieties and in on-going research to understand the mechanism(s) leading to this drought tolerance.
Symbiotic N2 fixation in soybean has been shown to be very sensitive to drying soil. The objective of this research was to screen a large number of plant introductions in an effort to identify soybean germplasm that might have substantially decreased sensitivity of N2 fixation to water deficits. A three-stage screening process was developed to successively narrow the number of candidate lines. The first-stage screen involved the measurement of petiole ureide levels in a large number of plant introductions (approx. 1000 per year). Approximately 10 percent of the lines with low petiole ureide levels, which are generally associated with N2 fixation tolerance, were selected. The second stage screen involved subjecting field plots of each selected plant introduction to a sustained water deficit of approximately 3 wk and measuring N accumulation during this period. Again, about 10 percent of these lines were selected for the intensive third-stage screen based directly on an acetylene reduction assay during a cycle of soil drying. From an initial population of about 3000 plant introduction lines, eight lines were identified as having substantial tolerance of N2 fixation to soil drying.