Silício e bactérias fixadoras de nitrogênio na qualidade de silagens de milho com e sem espiga

Abstract

This study aimed to evaluate the effects of inoculation with Azospirillum brasilense and the application of different silicon doses on the chemical composition, macro and micromineral composition, microbial population, fermentation profile, and aerobic stability of corn silages, with and without cobs. In the first chapter related to corn silage without cobs, the average contents of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and sodium showed no significant differences (P > 0.05) in any of the specific factors. The nitrogen content ranged from 1.57 to 1.62 g kg−1 between treatments with and without inoculation. For microbiology, the average counts of lactic acid bacteria (LAB) were 0.976 and 2.093 log10 CFU g−1 for silages without and with A. brasilense, respectively, with no significant effect (P = 0.171). Filamentous fungi (MOLD) counts ranged from 3,318 to 3,143 log10 CFU g−1 (P = 0.651) and yeast counts from 0.773 to 1,128 log10 CFU g−1 (P = 0.160). There was no interaction between silicon and inoculant (P > 0.05). Gas and effluent losses were reduced, and aerobic stability was maintained for over 120 hours. In the second chapter, concerning corn cob silage, a positive influence of inoculation with A. brasilense and increasing silicon doses on the fermentation profile and chemical composition was observed. Dry matter (DM) contents ranged from 45.3% to 48.7% (P = 0.041), with an increasing trend at higher silicon doses. Inoculation reduced N-NH3/TN levels, reducing protein release (P = 0.038). Fermentation losses were significantly lower (P < 0.05) in silages with inoculant and with 8 kg ha−1 of silicon, reflecting better dry matter conservation and lower effluent production. Aerobic stability showed a significant increase, exceeding 140 h for the combined treatments, while treatments without inoculant or without silicon reached only approximately 96 h before a 2 °C increase in silage temperature. The relationship between higher dry matter and lower fermentable substrate loss suggests that silicon contributed to the structural integrity of the grains and reduced undesirable microbial activity, while A. brasilense favored the rapid colonization by lactic acid bacteria and a consequent drop in pH. This synergy resulted in greater aerobic stability and maintenance of nutritional quality after silo opening. Overall, it can be concluded that the combination of silicon and A. brasilense is an efficient strategy for improving the improvement and conservation of corn silages, especially in the ear fraction, promoting increased dry matter, reduced losses, and greater aerobic stability, without compromising the nutritional value of the forage.