Abstract:
Soybeans were grown in hydroponic solutions and in perlite to
devise procedures to measure plant mineral accumulation and
solution depletion over time. Electron emission spectrometry and
micro-Kjeldahl-autoanalyzer analytic techniques were used to
monitor mineral content of individual plants and their corresponding
solutions. An automated computer assisted system of converting
raw data on either plant tissue or hydroponic solutions into amounts
of uptake for individual macronutrients was devised. Uptake
calculated from depletion measurements was similar to uptake
determined from plant mineral accumulation during the uptake
periods that were evaluated. Both analytic procedures are sensitive
enough to measure small increments in mineral uptake.
MES buffer (2-N morpholinoethanesulphonic acid) at 5 mM
adequately maintained pH in 50 ml volumes of aerated solutions used
for nutrient uptake experiments. MES at 1.5 mM was ineffective.
At 5 mM, MES did not affect growth or uptake of most macronutrients.
Potassium uptake, however, was enhanced by the MES
buffer in non-nodulated seedlings.
When seedlings are grown in the absence of fixed nitrogen,
nodulation causes seedlings to proportion more of the seed nitrogen
reserve to the roots. Smaller nodulated root systems initially
result in lower mineral uptake and less plant biomass production.
Eventually, nodulated plants reach a similar size to their non-nodulated
counterparts, but they do not show a growth advantage
until nitrogen fixation has been active for some time. Even though
total absolute amounts of nitrogen in the nodulated plants are higher
than those in non-nodulated seedlings, the nitrogen increase is not
reflected immediately in increased growth.
