Effect of nitrogen concentration and growth regulators on growth and nitrate content of lettuce.

Lettuce plants (Lactuca sativa L. cv. 'Paris Island') were grown in an unheated plastic greenhouse to determine the effects of solution nitrogen concentration and growth regulators (gibberellin and kinetin) on growth (fresh and dry head weight) and tissue nitrate content (TNC). The plants were grown in plastic containers with perlite and supplied with a basic nutrient solution supplemented with nitrogen (N) corresponding to 50, 100, 150, and 200 ppm NO3-N. Growth regulators; gibberellin (GA3) and kinetin were applied at different doses independently and in combination. Fresh, dry weight and TNC were responsive to N application level. However, fresh and dry weights were similar at 150 and 200 ppm and TNC at 100 and 150 ppm nitrogen supply. Gibberellin (GA3) and gibberellin and kinetin in combination (GA3+kinetin) enhanced fresh and dry weight and TNC compared to the control. There were few differences in response to application rates. Therefore, where lettuce plants are grown in similar conditions and low NO3 accumulation is desirable, together with high yield and good size, the best N application level is 150 ppm NO3-N and growth regulators application may enhance yield. However their use in reducing the nitrate content is not recommended.