Growth of a tomato crop at reduced nutrient concentrations as a strategy to limit eutrophication

In tomato (Lycopersicon esculentum L. cv Trust F1), effects of various nutrient treatments on growth, fruit yield and quality, nutrient uptake and accumulation were studied in a hydroponic system. Reductions of macronutrient concentrations to 50% (0.5 x C) or 25% (0.25 x C) of the control (C) levels as well as cessation of replenishment of the feed solution for the last 16 days after 7 months growth at control levels, had no adverse effect on growth, fruit yield and fruit quality. However, reduction of macronutrient concentration to 10% of control (0.1 x C) reduced fruit yield by similar to 30%. Steady-state influx and net flux of NO3- into the roots of 4-6 week-old seedlings had not acclimated and showed concentration dependence from 1.1 mM (0.1 x C) to 11 mM(C). Whereas, Pi and K+ fluxes were similar at 0.5 x C and C levels, at 0.1 x C they were significantly lower than the fluxes at higher concentrations, showing lack of acclimation at this concentration. This lack of flux acclimation may account for the adverse effects of low concentration (0.1 x C) on yield. The results have been discussed in the context of eutrophication and it is suggested that in a non-recirculating hydroponic system, NO3-, Pi, and K+ levels can be reduced to 25% of the concentrations currently being used in commercial greenhouses (C). In a recirculating system, the crop may be grown at control levels and used to deplete the feed solution for similar to 3 weeks prior to release of the solution to the drain.