Moisture Stress and N Redistribution in Soybean1

Abstract

AbstractThe redistribution of N from vegetative plant parts to the developing seed of soybean [Glycine max (L.) Merr.] may influence the duration of seed filling and yield. The objective of this study was to investigate the effect of moisture stress during various developmental stages on N redistribution. Soybean (cv. Williams) was grown in the field at Lexington, Ky., for 3 years (1979 to 1981) on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) soil. Irrigated controls were compared with moisture stress treatments from planting to beginning seed fill (growth stage R5), during seed filling (growth stage R5 to R7) or throughout the growing season. Stress was applied by not irrigating until the soil water potential reached – 300 9 kg−1 or by covering the soil with black plastic after emergence to allow severe stress to develop. Plant weight at growth stage R5 and yield were affected by the moisture stress treatments; however, moisture stress had only a limited effect on N concentration in the plant tissue. The proportion of seed N that came from redistribution varied among treatments and years from 33 to 102% and there was no consistent relationship between the level or timing of moisture stress and the contribution of redistributed N to seed N. The proportion of the N in the vegetative plant and pod walls that was redistributed was nearly constant across treatments and years. The data suggest that the contribution that redistributed N makes to the seed N at maturity is more closely related to the amount of N available for redistribution than it is to the ability of the plants to obtain N from the soil or via N2 fixation during seed filling.