The nitrate (NO3-) uptake rates of intact, 23 day old rice plants were
measured to determine the relationship between the plant's NO3- nutri
tion history and the NO3- uptake rate. A system for measuring NO3- upt
ake was designed, built and tested. Specific design goals, which were
met, include: low handling shock to the plants, high measurement accur
acy (4%), high temporal resolution (10 min) and minimal mass-transfer
limitations to uptake. Important design factors were identified and th
e overall uncertainties in the reported measurements were computed. Th
e observed uptake rates were dependent on the NO3- concentration ([NO3
-]) to which the plants were exposed for the 24 h prior to testing; pl
ants pretreated at higher [NO3-] had lower uptake rates from 200 mu M
NO3- solutions than plants pretreated at lower [NO3-].