Growth of a lettuce crop at low ambient nutrient concentrations: A strategy designed to limit the potential for eutrophication

A lettuce crop (Lactuca sativa L. cv. 'Sitonia') was grown hydroponically using the Nutrient Film Technique (NFT) in greenhouse experiments designed to investigate the effects on growth and elemental accumulation of reduced concentrations of nitrogen (N), phosphorus (P), and/or potassium (K) in the nutrient supply. The concentration of these elements was varied ever a 100-fold range, either separately or simultaneously; the highest concentration (Control) being that used by local commercial hydroponic lettuce growers. Reductions in the external concentrations of these elements (below Control) had no adverse effect on growth, rates of uptake, and accumulation of N, P, and K, and hence, utilization efficiency of these elements. External concentrations of N, P, and K may, therefore, safely be reduced to 1/10th of the Control in a recirculating hydroponic system; in non-recirculating systems, they may be reduced to 1/100th of the control.