Use of a Concerning Sewage Sludge in the Manufacture of Organomineral Fertilizers: Agronomical Implications and Sustainable Disposal

Proper sewage sludge (SS) disposal is a concern in tropical regions where there is higher population growth. Use an SS having concerning Zn and Ni contents in the manufacture of organomineral fertilizers (SS-OMFs) to be used in tropical depleted on these nutrients. The effects of SS-OMF rates (40, 60, 80, 100, and 120%, in relation to P 2 O 5 and K 2 O needs) and physical forms [powder (Pw), granule (G), and pellet (Pt)] on biological (C from microbial biomass, soil basal respiration, and urease activity) and chemical (nutrient uptake and trace elements) indicators of soil quality, as well as on soybean development were evaluated during 60 days in two tropical soils (a clay and a sandy clay loam). Two mineral fertilizations were added [NPK and NPK plus B and Zn (NPK B+Zn )]. Results: Organomineral fertilizer rates consistently increased biological indicators of soil quality and soybean vegetative development. Its application rate will depend on the soil texture, i.e., 70% of full P rate was more suitable for the clay soil whereas 100% was for the sandy clay loam. The powder form tended to be more advantageous in terms of supplying P, S, and Zn to soybeans, but N and K may leach. Pelletization could be a workable strategy to avoid it. Organomineral fertilizers based on sewage sludge seem to safely supply Zn and Ni to soybeans even when concerning concentrations are present, but its safety under real application routine remains to be proved. SS-OMF manufacture is a safe strategy for warrantying nutrient and organic matter recycles in tropical regions that are highly dependent on the importation of mineral fertilizers.