CO2 emissions represent one of the greenhouse gases significantly affecting climate change. Reduced tillage practices can contribute to the mitigation of CO2 emissions from soils. The effect of tillage practices with different straw incorporation on CO2 emissions was studied in field experiments in the years 2020 and 2021. The winter wheat straw was used in 2020, and spring barley straw in 2021. Treatments were: (1) chiselling to 10–12 cm; (2) shallow chiselling (5–6 cm depth); (3) straw mulch, and (4) stubble. The chiselling to 10–12 cm in the warm summer period of 2020 increased the CO2 emissions from soils even twice in comparison with other used soil tillage practices. The soil temperature and CO2 emissions decreased in the following order: chiselling to 10–12 cm < shallow chiselling ≤ stubble ≤ mulch in 2020. Low CO2 emissions without significant differences among treatments were observed in the year 2021 when low soil temperatures and excessive soil water content filling soil pores caused by intensive precipitations (23 mm) coming shortly after soil tillage were observed. The CO2 emissions from soils are affected by a number of factors. Among them the current weather conditions as well as soil temperature the depth of soil tillage and handling of postharvest residues, are important.