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The use of organomineral fertilizer can promote increments of organic matter and affect the enzymatic activity of the soil. The objective of this research was to evaluate the effect of organomineral and mineral fertilizer with humic substances on soil organic matter fractions and enzymes activities. The study was set up in a Xanthic Ferrasol, in the Cerrado region, Brazil. Treatments consisted of two fertilizers and four rates of P fertilizer. The following fertilizers were studied: mineral fertilizer enriched with humic substances (03% of N, 25% of P2O5, 08% of K2O, with 1% humic substance); and granulated organomineral produced from poultry litter and mineral fertilizer (MAP – mono-ammonium phosphate, with 26.6% of P2O5 and 18.2% of organic carbon). Five rates of P were also evaluated (0, 20, 40, 60, and 80 kg ha−1 of P2O5). The crop production, soil organic matter fraction and enzymes were assessed in the 2014/2015 and 2015/2016 growing seasons. Contents of the total organic carbon, particulate organic carbon, humic acid, fulvic acid, and maize and soybean grain yield were positively influenced by the fertilizer application. Fertilization treatments did not affect the enzymes activities, but they showed positive correlations with particulate organic carbon. [ABSTRACT FROM AUTHOR]