When ensiling alfalfa with a dry matter content of 36.5%, the effect of silage additives on the quality of fermentation and aerobic stability was tested. The temperature during the fermentation, and for 7 days after exposure to the air silage, was continuously measured by battery sensors with an accuracy of 0.065 °C. After 3 weeks of fermentation, the control silages without the additive already had a temperature about 1 to 1.5 °C higher than the silages with the additive, and so it remained throughout the fermentation. Control silages had a higher ash content and a higher continuous temperature during fermentation than other variants with biological and Chemical additives. According to temperature measurements, both control and all experimental silages were aerobically stable for seven days after exposure to air.