Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/1996
Publication Date: N/A
Citation: Interpretive Summary: One reason that soybean is a major crop in the world is its ability to symbiotically fix atmospheric nitrogen for use by the plants. Therefore, fertilizer nitrogen need not be provided to the crop. Recent research has shown that symbiotic nitrogen fixation in soybean is especially sensitive to soil drying. Even modest water deficits in the soil result in losses of nitrogen fixation activity. It was discovered by a USDA-ARS, Gainesville, FL scientist that in greenhouse tests the cultivar Jackson does not exhibit the usual extreme sensitivity of nitrogen fixation to soil drying. The experiments reported in this paper extend this discovery to field conditions to determine if the tolerance of Jackson was also expressed when grown in the field. The results of this experimentation confirmed the superiority of Jackson under drought conditions.
Technical Abstract: Substantial evidence has accumulated that N2 fixation in soybean is much more sensitive to drying soil than is leaf gas exchange and plant mass accumulation. In contrast, the soybean cultivar Jackson in controlled environments has been found to have N2 fixation sensitivity to drying soil that is approximately equivalent to the sensitivity of leaf gas exchange. This study was undertaken to determine if the superiority of Jackson was expressed under field conditions. N2 fixation activity was measured by in situ acetylene reduction rates and shoot N accumulation. Leaf gas exchange was measured as stomatal conductance and shoot mass accumulation. All measures in this field study indicated that N2 fixation in Jackson was decreased in response to soil drying in about the same proportion as leaf gas exchange. These results with Jackson were in contrast to those with the cultivar Biloxi in which N2 fixation was decreased to a greater extent by drought than was leaf gas exchange.