LAUSR

ABSTRACT Composting of by-products from the sugarcane (Saccharum officinarum) industry can help achieve sustainable biofuel production by replacing mineral fertilizers and adequate residual disposal. The hypothesis was that the compost of filter cake and ash enriched with/without phosphate rocks (apatite-A and phosphorite-P) and phosphate-solubilizing bacteria can replace mineral P fertilizers and improve sugarcane production. A compost was produced from a mixture of filter cake and ash in 60 days of composting. The compost + A and the compost + P (with/without bacteria) were applied at sugarcane planting to supply 150 kg ha-1 P2O5. Yield and quality of sugarcane, soil P dynamics, and enzyme activities in the soil were monitored. Results showed that the application of 20 Mg ha-1 of compost increased sugarcane yield (up to 6 %) and β-glucosidase activity (up to 15 %) when compared to mineral control. Adding phosphate rock in compost allowed a reduction in the total compost amount from 20 to 10 Mg ha-1, with similar yields. Bacteria inoculation increased sugarcane yield (up to 5 %) and acid phosphatase activity (up to 6 - 18 %), enhancing the soil P availability. Compost + P increased labile and moderately labile P contents with a reduction of the acid phosphatase activity. The increase of soluble P (available-P) in the soil is an important gain because most P is fixed (unavailable) in tropical soils. The study revealed a great potential for optimizing by-products generated by the sugarcane industry with the enrichment of compost (adding phosphate rock and phosphate solubilizing bacteria), reducing the dependency of sugarcane production on finite P mineral reserves.