The aim of the experiment was to find out how cutting length wilted lucerne and the addition of additives affect the quality of the fermentation and aerobic stability of silage. The temperature with the accuracy of 0.065 °C was measured continuously during the fermentation and aerobic degradation. Besides checking without additive was tested the effect of 3 chemical and 2 biological additives. To determine the length of cut was used Penn State Particle Size Separator. After separation of the silage with longer chop (D) remaining 77.5 % of the mass on the sieve 19 mm, shorter chop (K) 26.7 %. For silage D compared with K at the beginning of the fermentation the temperature increased slowly (peaked 72 hours later) and slowly decreased (after 119 days of the experiment, the temperature D was higher by 2 °C). Aerobic stability D was lower by 54 hours. The temperature of silage was affected by additives, but not so much that the difference between D and K in the dry matter content, nutritional value, quality of fermentation and aerobic stability were statistically significant.