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 hydroponica lly using the Nutrient Film Technique (NFT) in greenhouse experiments designed to investigate the effects on growth and elemental accumulati on of reduced concentrations of nitrogen (N), phosphorus (P), and/or p otassium (K) in the nutrient supply. The concentration of these elemen ts was varied ever a 100-fold range, either separately or simultaneous ly; the highest concentration (Control) being that used by local comme rcial hydroponic lettuce growers. Reductions in the external concentra tions of these elements (below Control) had no adverse effect on growt h, rates of uptake, and accumulation of N, P, and K, and hence, utiliz ation efficiency of these elements. External concentrations of N, P, a nd K may, therefore, safely be reduced to 1/10th of the Control in a r ecirculating hydroponic system; in non-recirculating systems, they may be reduced to 1/100th of the control.