High temporal resolution measurement of nitrate uptake from flowing solutions

The nitrate (NO−3) uptake rates of intact, 23 day old rice plants were measured to determine the relationship between the plantʹs NO−3 nutrition history and the NO−3 uptake rate. A system for measuring NO−3 uptake was designed, built and tested. Specific design goals, which were met, include: low handling shock to the plants, high measurement accuracy (4%), high temporal resolution (10 min) and minimal mass-transfer limitations to uptake. Important design factors were identified and the overall uncertainties in the reported measurements were computed. The observed uptake rates were dependent on the NO−3 concentration ([NO−3]) to which the plants were exposed for the 24 h prior to testing; plants pretreated at higher [NO−3] had lower uptake rates from 200 μ NO−3 solutions than plants pretreated at lower [NO−3].