Measurement of Ammonium Ions in Flowing Solution Culture and Diurnal Variation Uptake byLolium perenneL

An existing system of flowing solution culture, in which pH and the concentration of several nutrient ions are automatically monitored and controlled, has been extended to include $NH4+$ at 10 mmol N m⁻³. A brief account is given of the use of the equipment with a simulated sward of perennial ryegrass (Lolium perenne L.). Uptake of $NH4+$ measured over three successive days in June, varied with daily solar radiation and exceeded 1000 mg N m⁻² d⁻¹. The uptake of $NH4+$ showed a pattern of diurnal variation similar to the variation in solar radiation, but with a lag period for uptake of 5 h. Hourly uptake rates ranged from 32 to 67 mg N m⁻²h⁻¹ and solar radiation from 0 to 2.8 MJ m⁻² h⁻¹. During a 24 h period, additional measurements were made of K⁺ uptake and net H⁺ efflux, both of which showed patterns of diurnal variation with lag periods of 6 h hand 7 h, respectively. The stoichiometric ratio of the sum of $NH4+$ and K⁺ to the net efflux of H⁺ was 1.02: 1.