The aim of the research was to determine the exchange rate of carbon dioxide between the atmosphere and the maize field fertilized with digestate from an agricultural biogas plant. The studies considered both the amount of net carbon dioxide emission which is the difference between the amount of this gas absorbed by vegetation and its amount emitted from the whole ecosystem of the field as well as the emission resulting only from changes occurring in the soil. CO2 emission from entire field was measured by the eddy covariance method with a set of LI-7500A analyzer (LI-COR Biosciences, USA) for measuring CO2/H2O concentration in air and 3-axis WindMaster ultrasonic anemometer (GILL, UK). The data from the analyzers were recorded at 10Hz, while the CO2 streams were calculated using the EddyPro 5 software. The soil emission was determined with the chamber method using the automated ACE measurement system (ADC BioScientific, UK). Until the maize reached maturity, the study was carried out once a week, at 10.00 - 14.00. During each measurement day, the basic meteorological parameters were also measured. The obtained results showed a clear relationship between plants development phase and the size of the net CO2 exchange. Negative values of carbon dioxide streams, indicating the absorption of this gas from the atmosphere, were observed already in the case of plants with a height of approx. 25 cm, while the maximum values were reached after the release of panicles by maize. The carbon dioxide emission from soils, measured at the same time was maintained throughout the entire research period at a similar low level, undergoing only slight fluctuations associated with variable soil moisture. The study showed that the maize field, almost throughout all growing season, can be treated as a sink of atmospheric carbon dioxide, reducing its emission from agriculture.