Fertilizantes granulados à base de biocarvão com aglutinantes agroindustriais para melhorar a eficiência de uso do fósforo e a saúde de solos tropicais

Abstract

Phosphorus (P) is rapidly fixed in highly weathered Oxisols, resulting in low nutrient recovery efficiency from soluble fertilizers. Biochar has been proposed as a matrix for slow-release fertilizers; however, its application in powder form poses operational limitations, such as particulate matter emission and wind-drift losses. Therefore, the objective of this thesis was to develop and evaluate biochar-based granular fertilizers (BBGFs) produced from eucalyptus charcoal fines (Eucalyptus urograndis) and reactive natural phosphate at a 3:1 ratio (w/w), using three agro-industrial binders: cassava wastewater (CW), pyroligneous extract (PE), and bio-oil (BO). Three complementary studies were carried out in a dystrophic Red-Yellow Oxisol under Cerrado vegetation. In the first, the granular properties of BBGFs produced with five binder proportions (50, 75, 100, 125, and 150% of the biochar–phosphate mixture weight) were evaluated in a completely randomized design (CRD), 3 x 5 factorial scheme; the granules with the most favorable attributes (75 to 150%) were selected for a bioassay with common bean (Phaseolus vulgaris L., cv. BRSMG Uai) in a CRD, 3 x 4 + 4 factorial scheme (three binders, four proportions, and four controls: unfertilized soil, natural phosphate, biochar + natural phosphate, and biochar alone). In the second, BBGFs were incubated for 10 and 40 days in a CRD, 3 x 4 + 4 factorial scheme, to assess β-glucosidase, acid phosphatase, and arylsulfatase activities, as well as soil chemical properties. In the third, the agronomic effectiveness and residual effect of BBGFs were evaluated over five successive cropping cycles of Urochloa brizantha BRS Paiaguás in a randomized block design, 3 x 4 + 4 factorial scheme, including a soluble P control (KH2PO4). BO granules exhibited the highest crushing strength and density, whereas PE granules showed the highest salinity index. BBGFs promoted increases in shoot and root dry matter of common bean compared to unfertilized soil, particularly BBGFs-PE, which increased shoot and root biomass by 123.73% and 755.17%, respectively. In the second study, all formulations enhanced enzymatic activities above controls, with increases exceeding 8%. BBGFs-BO at 150% maintained the most stable enzymatic activity over time. BBGFs-CW were the most effective in increasing available P (24.0 mg kg⁻¹), while BBGFs-BO and BBGFs-PE enhanced soil organic carbon and cation exchange capacity by up to 430% and 163%, respectively. In the third study, BBGFs-PE at 125% and 150% achieved relative agronomic effectiveness of 96.8% and 101.3%, respectively. At the 150% proportion, BBGFs-PE increased total P uptake by 6.5% over KH2PO4. BBGFs-CW exhibited an initial low-release phase, with agronomic recovery from the fourth cycle onward. BBGFs-BO restricted biomass production at the highest binder proportions but promoted the highest Soil Quality Index. BBGFs-PE at the 125 and 150% proportions represent the most balanced alternative for replacing soluble phosphate sources, as they combine agronomic effectiveness, sustained P supply, and improved soil quality.