Interactive effectiveness of microbial fertilizer enriched in N on lettuce growth and on characteristics of an Ultisol of the rainforest region

To improve yield and nutrient absorption, the addition of fertilizers is recommended to provide nutrients in adequate quantities. An alternative substitution for conventional fertilizer is the use of Acidithiobacillus bacteria to produce rock biofertilizer that is subsequently mixed with organic matter inoculated with diazotrophic bacteria (Beijerinckia indica) and with Mucorales fungus (Cunninghamella elegans) for nitrogen enrichment and plant protection. This study evaluates the effectiveness of microbial fertilizer on nutrient uptake and its interaction with consecutive cycles of grown lettuce on an Ultisol in the Brazilian rainforest region. The experiment used eight fertilizer treatments (biofertilizer and conventional soluble fertilizer) applied at three rates (50%, 100% and 150% of the recommended rate (RR) and a control treatment of earthworm compost (2.4 L plant(-1)), in four replicates. The total N, P and K in plants leaves, as well as pH, total N and available P and K in soil samples, were measured. The microbial fertilizers (biofertilizer and bioprotector) showed similar effects, as did the conventional soluble fertilizer, on nutrient uptake in the lettuce leaves and on the soil samples. A residual effect was observed, and the microbial fertilizers increase lettuce characteristics in the three cycles compared with the conventional fertilizer. We concluded that the microbial fertilizer enriched in N by inoculation with B. indica may be a viable alternative for the replacement of conventional soluble fertilizers in lettuce grown in an Ultisol of the rainforest region.