Effects of drought stress and re-watering on nitrogen content in soybean at different growth stages.

Drought stress is a major limiting factor for soybean (Glycine max (L.) Merr.) growth and yield in arid and semiarid regions. This study investigates the N content in different organs and the yield impact of two droughttolerant soybean cultivars, Hei Nong44 and Hei Nong65, under varying drought intensities and re-watering at different growth stages. The results indicate that the effect of drought stress on N content varies with growth stage and organ. During the seedling and flowering stages, the ammoniacal N content in leaves and petioles of both cultivars generally decreased, with a reduction of 16.04%-21.95% during seedling stage and 6.46%-23.52% during flowering stage under severe drought (S), while it increased in stems. The nitrate N content in leaves peaked under moderate drought during the seedling stage and under severe drought during the flowering stage, increasing by 20.00% and 16.21%, 15.71% and 55.56% for 'Hei Nong44' and 'Hei Nong65', respectively, while it decreased in stems. During the pod-filling stage, ammoniacal N content increased in leaves and stems, with an increase of 20.99%-60.13% under S, while it showed a rising-then-falling trend in pods. Nitrate N content had the highest increase in leaves and stems, rising by 67.02%-69.31% under S, while it decreased in petioles with increasing drought severity. After re-watering, both cultivars showed some recovery in N content. Yield reduction was more significant during the flowering and pod-filling stages, decreasing by 17.45%-32.66% and 21.47%-35.63%, respectively. [ABSTRACT FROM AUTHOR]