Resumen

ESCALONA, Argelia et al. Effects of the nitrogen sources on lettuce nitrates content and over "spad" lectures. Agronomía Trop. [online]. 2009, vol.59, n.1, pp.99-105. ISSN 0002-192X.

The accumulation of nitrate on lettuce leaves is considered as a response of the amount and type of the N source: the nitrate level could be identified through "SPAD" lectures. The objective of the current research was to compare the influence of different N fertilizers sources over the nitrates levels in lettuce leaves and the use of "SPAD" lectures to evaluate it. We carried out an experiment with lettuce, Great Lakes 659 variety, in a locality of Sanare, "Andrés Eloy Blanco" county, Lara State, where the impact of four types N fertilizers (Calcium Nitrate and Ammonium Sulphate with or without a complementary organic amendment, urea, and 15-15- 15) at a dose of 200 kg ha^-1, on the content of nitrate in the leaf was evaluated. The relationship between the content of nitrates in leaves and the "SPAD" lectures, and of these with the fresh and dry weight were also evaluated. We found that the N source affects the content of nitrate (91 mg kg^-1) on dry weight basis and in fresh weight (466 mg kg^-1), and lectures with "SPAD" (29,070 and 21,600 units), in external and internal leaves respectively. In conclusion, the calcium nitrate fertilizer produced the higher "SPAD" lectures as well as the higher nitrates content. The amount and sources of N used, do not exceed the limits values of the European Community for lettuces growing in open fields, and they could be used without risks for human health.

Palabras clave : Lactuca sativa L; organic amendment; nitrate content; greenery.