Nitrogen accumulation and nodule activity of field-grown 'Jackson' soybean in response to water deficits

Substantial evidence has accumulated that N-2 fixation in soybean (Glycine max Merr.) 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 N-2 fixation sensitivity to drying soil that is approximately equivalent to the sensitivity of leaf gas exchange. This study was undertaken to determine if Jackson behaved in a similar way under field conditions. N-2 fixation activity was measured by in situ acetylene reduction rates and N accumulation in shoots. Leaf gas exchange was measured as stomatal conductance and shoot mass accumulation. All measures in this field study indicated that N-2 fixation in Jackson 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 N-2 fixation was decreased to a greater extent by drought than was leaf gas exchange. (C) Elsevier Science B.V. All rights reserved.