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.
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Hatch et al. (1986) studied this question.