AbstractThe activity of seminal and nodal root systems of winter wheat (cv. Avalon) in taking up NO3−and K+has been measured in solution culture using a split root technique.Plants in the tillering phase of growth (36 days old) were used for the experiment which lasted 20 days. During this time plant dry weights increased by a factor of 20, whilst root: shoot ratios and nutrient compositions remained constant. Inflows (uptake rate per unit root length) were 2–6 times higher for the nodal roots than for the seminal roots, with values varying between 1 and 9 pmol cm−1s−1for N and between 0.5 and 4 pmol cm−1s−1for K. When uptake was expressed on the basis of unit fresh weight of roots, values ranged from 1 to 2.3 pmol mg−1s−1for N and from 0.4 to 1.0 pmol mg−1s−1for K, and there were only very small differences in uptake efficiency between the nodal and seminal roots.Uptake rate per unit root decreased with plant age. This was caused by a decline in shoot demand due to the reduction of the relative growth rate.When either the nodal or seminal root system alone was supplied with nutrients, uptake rate per unit root increased and nutrient uptake per plant reached 72