Influence of nitrogen fertilization in the absorption of nitrogen and nitrate accumulation on iceberg lettuce

摘要

Yield response and plant nitrate concentration were studied for nitrogen doses of 25, 50, 100, 150, and 200 kg.ha~(-1) applied in fertigation. Crop yield increased with N dosages up to 100 kg.ha~(-1), obtaining 53.4 t.ha~(-1) of green biomass and 33.1 t.ha~(-1) of commercial lettuce heads. However, with 150 and 200 kg.ha~(-1) N applications, the biomass and yield index decreased. The NO_3~- content in the soil solution (soil: water extract 2:1) increased with the 150 and 200 kg.ha~(-1) N applications, and decreased when the quantities of N provided were 25 and 50 kg.ha~(-1). The concentration of NO_3~- remained uniform during the growth cycle when 100 kg.ha~(-1) of nitrogen were added, and the availability of NO_3~- was balanced with the absorption by the plant. Plant N absorption increased significantly between the 25 and 50 kg.ha~(-1) treatments and those of 100, 150 and 200 kg.ha~(-1) of N. However, there were no significant differences among the latter treatments. The outer leaves of the plants showed a nitrate concentration three times higher than that of the inner leaves, this concentration changed according to the quantity of nitrogen provided. At harvest the NO_3~-, concentration in outer leaves was of 1,635 to 4,494 ppm, and in inner leaves of 651 to 1,508 ppm for different quantities of N supplied.