Uptake of nutrients by lettuce on NFT with controlled composition of the nutrient solution.

An automatically-controlled recirculating NFT system was developed, consisting of a growth unit and a measuring and control unit. It is described together with some basic growth and uptake models. Results are presented of a preliminary experiment with the lettuce cultivar Sitonia (using manual control and nutrient dosage). The % DM in the heads decreased from 6.86 (week 1, 20 June 1988) to 3.89 (week 5, 25 July). The shoot:root ratio increased from 0.50 (week 1) to 6.47 (week 6). The time courses of DW increase and cumulative uptake of macronutrients were well described by exponential equations. The cumulative uptake determined from the loss of nutrients from the nutrient solution exceeded that determined from plant analysis. Cumulative uptake as a function of cumulative daily radiation was well described by a logistic equation. Some constant plant uptake ratios between micro- and macronutrients were observed: Cl uptake was related to that of N, K, P or Mg, and B uptake to that of K. DW as a function of transpiration was also well described by a logistic model, with an average DM production of 3.1 g/litre transpired; a logistic model also expressed transpiration as a function of radiation, with an average transpiration output of 5.8 litres/unit (kJ/cmsuperscript 2) increase in radiation. (Abstract retrieved from CAB Abstracts by CABI’s permission)