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Abstract
Although large quantities of nitrogen are required for high soybean [Glycine max (L.) Merr.] yields, yield increases with N fertilization are not easily achieved. Along with adverse effects on N‐fixation, N fertilization has been reported to stimulate excessive vegetative growth, especially in soybeans with the indeterminate growth habit. The objective of this study was to compare the influence of N application (150 kg N/ha, applied in irrigation water between growth stages Rl and R5) on morphological development of the indeterminate cultivar Weber and the semi‐dwarf determinate line 172–16. The two genotypes were morphologically similar at growth stage Rl (beginning bloom), but morphological differences were apparent from R3 (beginning pod stage) until maturity, with greater development of main‐stem and: branch lengths for Weber than for 172–16.’ For Weber, N fertilization greatly stimulated branch length; this was apparent at growth stage R3 and was associated with lodging and disease infestation. For the lodging‐resistant 172–16, which had essentially achieved final node numbers by R3, N had little effect on branching or main‐stem development. For Weber, substantial yield decreases have been associated with high inputs of N, whereas yields of 172–16 may be more stable or even enhanced as N availability increases. These results may be related to the differential influence of N on vegetative growth responses of these genotypes.
Notes
Joint contribution of the South Carolina Agric. Exp. Stn. (journal article no. 3075) and of the INRA Centre de Recherches Agronomiques de Toulouse. This work was performed during the sabbatical leave of SUW at INRA Station d'Agronomie, Toulouse.