The effect of doses and sources of phosphorus on crisphead lettuce production was evaluated in an experiment conduced in Santo Antonio do Amparo, Brazil, from June to September/98. The experimental design was of completely randomized blocks, in a 2x4 factorial scheme, with three replicates comprehending two sources of phosphorus [simple superphosphate (18% of P2O5) and magnesium thermophosphate (17% of P2O5)] and four doses (0; 300; 600 and 900 kg ha-1 P2O5). The total and commercial yield of lettuce, stem length and the circumference size of the commercial head were evaluated. Significant effects among doses and sources were observed for total and commercial yield. There was a quadratic regression for simple superphosphate where the doses of 672 and 617 kg ha-1 (P2O5) presented the highest total and commercial yield, respectively. As occurred with magnesium thermophosphate, a linear increase was found in yield. Using 583 kg ha-1 P2O5 resulted in greater stem length (6.75 cm) without impairing commercial value. Doses and sources of phosphorus did not present significant effect over commercial head circumference.
Lactuca sativa L.; yield; fertilization levels; simple superphosphate; magnesium thermophosphate
