NITROGEN ON GROWTH AND YIELD OF LETTUCE PLANTS GROWN UNDER ROOT CONFINEMENT

Resumo

The objective of this research was to test the hypothesis that when lettuce plants grow under root confinement its growth, development and yield is reduced and that such negative effects may be compensated by increasing nitrogen availability in the rooting media. The experiment was conducted between Augut 11^th and September  23^th 2011. Lettuce transplants, cv. Stella, bearing five leaves were planted in pots using sand as substrate. Treatments were three root confinement levels and five N concentrations in the nutrient solution, in a 3 x 5 factorial randomized experimental design. Root confinements were simulated by pots sizes of 2.5 dm³ (no confinement, the control); 1.0 dm³ (moderate) and 0.4 dm³ (severe). Nitrogen concentrations were: 5.55 (C1), 8.05 (C2), 10.55 (C3), 13.05 (C4) and 15.55 (C5) mmol L^-1. There were interactions among treatments and plants grown under severe root confinement supplied by the nutrient solution at the N concentration of 10.55 mmol L^-1 N reached similar leaf growth than those under no root confinement at 5.55mmol L^-1 N. Increasing the N concentration in the nutrient solution enhanced shoot growth but decreased root growth. It was concluded that increasing N fertilization rates is not enough to maximize lettuce growth and yield and that they have to be adjusted taken into account the actual conditions for root growth in the rooting medium.