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There is little information available concerning the effects of different sources and levels of phosphorus in the soil on lettuce quality and production. To help determine an optimal strategy, we used complete randomized blocks, in a 2x3x5 factorial experimental design, with two commercial lettuce cultivars widely used in Brazil (Americana (iceberg lettuce) cv. Lucy Brown and Crespa (leafy lettuce) cv. Vanda) fertilized with one of three phosphate sources [MAP, Polyblen or Triple Super Phosphate (SPT)], at five concentrations (0, 250, 500, 750 or 1000 kg of P 2 O 5 ha-1), with three replicates planted on a farm in Mineiros, GO. The variables stem height, head diameter, number of commercial and non-commercial heads and commercial fresh weight, were analyzed at 40 days after planting. There was a triple interaction for these factors, when their averages were broken down to qualitative and quantitative effects. The variables were correlated, and affinities with the genotype x phosphate source interaction were found. Based on the yield data, the recommendations for Americana are 911, 680 or 457 kg P 2 O 5 ha-1 from MAP, Polyblen, and SPT, respectively. For Crespa the recommendations are 580 or 611 kg P 2 O 5 ha-1 from MAP and SPT, respectively.

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