Nitrogen Flux into Corn Roots as Influenced by Shoot Requirement1

Abstract
Knowledge of the N flux characteristics of corn (Zea mays L.) roots is important in determining the N fertilizer practices needed for efficient N fertilizer use. Fertilizing a portion of the root system with N increases the N uptake required per unit of root fertilized over that in which all roots are fertilized with N. The effect that fertilizing a portion of the roots with N has on the N influx characteristics of corn roots has not been evaluated. Hence the objective of this research was to determine if shoot N requirement influenced N influx/m of corn root. Trimmed‐ and split‐root procedures were used in solution culture experiments in the growth chamber to vary the amount of N‐absorbing roots/unit of shoot and determine its effect on N influx. Both NH+4 and NO3 forms of N were used.Trimming corn roots 2 days before measuring influx resulted in only small increases in N influx/m of root so that N uptake/plant was greatly reduced by trimming. Splitting the roots between N‐containing and N‐free solutions from seedling stage until 16 or 18 days, when influx was measured, resulted in larger increases in net N influx than when the roots were trimmed 2 days before influx measurement. Nitrogen level within the root was not related to N uptake rate/m of root in either experiment.It appears that increasing shoot demand for N does not immediately affect N influx into the root but that the capability for higher N influx is developed when plants are grown under N stress.
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