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CROP PHYSIOLOGY & METABOLISM

Genotypic Variation for Shoot N Concentration and Response to Water Deficits in Soybean

Dep. of Crop, Soil, and Environmental Sciences, Univ. of Arkansas, 1366 W. Altheimer Dr., Fayetteville, AR 72704

^* Corresponding author (lpurcell{at}uark.edu)

For soybean [Glycine max (L.) Merr.], reports differ as to the degree to which accumulation of shoot biomass and N are inhibited by water deficit (WD). Our first objective was to evaluate responses of shoot biomass and shoot N to WD for soybean genotypes from diverse genetic backgrounds. The second objective was to determine if the severity of WD affected the response of N accumulation relative to biomass accumulation among genotypes. In a 2-yr field study of 15 genotypes, shoot N concentrations ranged from 25 to 33 mg N kg^–1 for plants from well-watered (WW) treatments harvested around 60 d after planting, and N₂ fixation accounted for 68% of the N accumulated. Following a 16- to 22-d WD period, shoot N concentrations were similar to that of WW plants for genotypes with low WW N concentrations but decreased for genotypes with high WW N. As a result, the shoot N concentration range among genotypes decreased following WD stress. In a greenhouse study where essentially all of the plant N accumulated was from N₂ fixation, shoot N concentration increased across a range of WD levels for six genotypes with low WW N concentrations but decreased for two genotypes with high WW N. These results indicate that changes in shoot N concentration in response to WD depend on both the inherent N concentration of a given genotype and the severity of the WD stress.

Abbreviations: FTSW, fraction of transpirable soil water • MG, maturity group • WD, water deficit • WW, well watered