Phosphorus fertilizer for lettuce grown in Ultisol in the state of Maranhão
The use of mineral fertilizers in lettuce is an agricultural practice that brings satisfactory results, however, one must know the optimal dose according to each soil type and its fertility. Thus, the objective was to evaluate the influence of phosphorus doses on the production of lettuce ‘Vera’, in soil with low phosphorus content (14 mg dm-3). The experiment was conducted from September 3 to October 18, 2011. The experimental design was randomized blocks, with six treatments (0, 50, 100, 200, 300 and 400 kg ha-1 P2O5) and four replications. The P content in the soil and leaf showed quadratic adjustments and increased with P supply up to 320 and 205 kg ha-1 P2O5, respectively. The fresh mass of shoots and dry mass of shoots and P accumulation also showed quadratic adjustment. The highest fresh mass of shoots and dry mass of shoots were obtained with doses of 283 and 292 kg ha-1 of P2O5, respectively. The accumulation of P for the lettuce with a dose that maximized fresh mass of shoots was 127 mg plant-1, or 8.8 kg ha-1 P, or 20 kg ha-1 P2O5.