9. Nitrogen Uptake in Soils under Different Water Table Depths

Abstract

A mathematical model was used to examine the interactions of NH₄+ transport to rice roots, as well as to calculate root length densities required to relate N uptake to concentrations of NH₄ + in solution around the rooting medium for three water treatments: water table 30 cm below the surface, 15 cm below the surface and a flooded system. Measured uptake was greatest for the plants under the 30 cm treatment, followed by the 15 cm treatment, then the flooded treatment. Solution concentrations were highest under the flooded treatment followed by the 30 cm treatment, then the 15 cm treatment. Calculated root length densities were greatest for the plants under the 30 cm water table treatment, followed by those under the 15 cm treatment, then the flooded treatment. Measured root length densities were similarly greatest for the plants under the 30 cm water table treatment, followed by those under the 15 cm water table depth treatment, then the flooded treatment. However, differences between measured and calculated root length densities became significant for all treatments after 30 days of treatment imposition. Transport rates varied with treatments but uptake rates did not reflect these differences in transport rates, thus, transport through the growth medium did not limit uptake of nitrogen by the plants.