Effect of nitrogen nutrition on growth and nitrate accumulation in lettuce(Lactuca sativa L.), under various conditions of radiation and temperature

A better understanding of the effect of environmental factors on growth and nitrate accumulation in plants is necessary to develop cultivation practic es, and in particular for providing lettuces with a low nitrate content. Th is study was conducted to analyse the effect of nitrogen supply on the inte rception and conversion of the PAR in dry matter, and on the nitrate and wa ter accumulations in fresh tissues of the lettuce, for various conditions o f temperature and radiation. The growth, and water and nitrate concentratio ns of two soilless cultures of lettuce (summer and autumn) were measured fo r two levels of radiation and two levels of nitrogen supply. RUE ranged fro m 2.12 to 3.50 g.MJ(-1), being higher for a low radiation level and for a h igh nitrogen supply. There was a positive correlation between the lettuce n itrate and water contents. The slope of this relationship was not affected by environmental conditions, indicating a strong interdependance between ni trate and water accumulation in lettuce.