Control of relative growth rate by application of the relative addition rate technique to a traditional solution culture system

Abstract

The relative addition rate (RAR) technique allows the nutritional control of plant relative growth rate (RGR) by the provision of nutrients at exponential supply rates. The technique, however, was developed with technologically sophisticated aeroponic systems. In this paper, we report on experiments used to adapt the RAR technique to a conventional solution culture system. A background concentration requirement of 36 μM nitrogen (N), with other nutrients supplied in proportion to N, was necessary to produce a constant RGR of Triticum aestivum L. (wheat) at a low RAR. Solution pH changes were reduced by increasing the percentage of NH4 in the nitrogen supply, but the plants exhibited dry weight reductions and symptoms of toxicity above 30% NH4. For wheat, a ratio of 25/75 NH4/NO3 was optimum for minimizing pH changes within the nontoxic range. A test of the effectiveness of the RAR technique using this background concentration and NH4/NO3 ratio showed that RGR increased with RAR with a linear slope of 0.55 and an intercept of 0.07 d-1. Although the relationship between growth rate and nutrient supply was less than the one-to-one dependence of RGR on RAR that has been obtained with more sophisticated apparatus, application of the RAR technique to a conventional solution culture system still affords considerable control of RGR and presents a simple method for growing plants at different levels of nutrient stress and at distinct RGRs.