Production of rock biofertilizers is a practical process with reduction of energy consumption and increasing nutrients availability in soils. To evaluate the agronomic efficiency and the residual effect of P rock biofertilizer (PB) and potash rock (KB), compared to simple superphosphate (SSP) and potassium chloride (KCl), a field experiment with two consecutive lettuce crops (cv. Grand Rapids) was carried out in a soil at Cariri (Ceará, Brazil), from August to September 2005. The mineral fertilizers were applied in the levels recommended for lettuce (SSP and KCl), and the biofertilizers in three levels (PB1 and KB1 half of recommended levels; recommended levels PB2 and KB2 and 150% the recommended level PB3 and KB3 for SSP and KCl) and a control treatment with no P and K (P0K0). The experimental design was a factorial 5² in the randomized block, with four replicates. There was similar performance of the PK rock biofertilizers compared to the mineral fertilizers, especially when the level BP2BK3 was applied. The consecutive crop showed residual effect on lettuce yield (fresh shoot biomass), height, number of leaves, commercial evaluation, and P and K accumulation on shoot dry biomass. The results suggest that P and K rock biofertilizers may be used as an alternative in mineral fertilization.
Lactuca sativa L.; Cariri of Ceará; PK fertilizers; available P and K; semiarid
